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Taxon author: Rydb.

ITIS records citing taxon author "Rydb."
 
 Kingdom Plantae
  Abronia pumila Rydb. -- not accepted
  Abronia salsa Rydb. -- not accepted
  Achillea alpicola (Rydb.) Rydb. -- not accepted
  Achillea angustissima Rydb. -- not accepted
  Achillea fusca Rydb. -- not accepted
  Achillea lanulosa ssp. alpicola (Rydb.) D.D. Keck -- not accepted
  Achillea lanulosa var. alpicola Rydb. -- not accepted
  Achillea millefolium var. alpicola (Rydb.) Garrett -- not accepted -- common yarrow
  Achillea millefolium var. fusca (Rydb.) G.N. Jones -- not accepted
  Achillea millefolium var. pacifica (Rydb.) G.N. Jones -- not accepted -- Pacific yarrow
  Achillea millefolium var. puberula (Rydb.) Nobs -- not accepted -- common yarrow
  Achillea nigrescens (E. Mey.) Rydb. -- not accepted
  Achillea occidentalis (DC.) Raf. ex Rydb. -- not accepted
  Achillea pacifica Rydb. -- not accepted
  Achillea puberula Rydb. -- not accepted
  Acmispon americanum (Nutt.) Rydb. -- not accepted
  Acmispon americanus (Nutt.) Rydb. -- accepted -- American bird's-foot trefoil
  Acmispon americanus var. americanus (Nutt.) Rydb. -- accepted -- American bird's-foot trefoil
  Acomastylis rossii ssp. turbinata (Rydb.) W.A. Weber -- not accepted
  Aconogonon phytolaccifolium var. phytolaccifolium (Meisn. ex Small) Small ex Rydb. -- accepted -- poke knotweed
  Aconogonum phytolaccifolium (Meisn. ex Small) Small ex Rydb. -- not accepted
  Acrolasia albicaulis (Hook.) Rydb. -- not accepted
  Acrolasia gracilis Rydb. -- not accepted
  Agastache pallidiflora (A. Heller) Rydb. -- accepted -- Bill Williams Mountain giant hyssop
  Agastache pallidiflora ssp. pallidiflora (A. Heller) Rydb. -- accepted -- Bill Williams Mountain giant hyssop, pallid flower giant hyssop
  Agastache pallidiflora ssp. pallidiflora var. pallidiflora (A. Heller) Rydb. -- not accepted -- Bill Williams Mountain giant hyssop, pallid flower giant hyssop
  Agastache pallidiflora var. pallidiflora (A. Heller) Rydb. -- accepted -- Bill Williams Mountain giant hyssop
  Agoseris glauca var. asper (Rydb.) Cronquist -- not accepted
  Agoseris glauca var. parviflora (Nutt.) Rydb. -- not accepted
  Agoseris rostrata Rydb. -- not accepted
  Agoseris turbinata Rydb. -- not accepted
  Agrimonia bicknellii (Kearney) Rydb. -- not accepted -- Bicknell's groovebur
  Agrimonia macrocarpa (Focke) Rydb. -- not accepted
  Agropyron andinum (Scribn. & J.G. Sm.) Rydb. -- not accepted
  Agropyron inerme (Scribn. & J.G. Sm.) Rydb. -- not accepted
  Agropyron latiglume (Scribn. & J.G. Sm.) Rydb. -- not accepted
  Agropyron leersianum (Wulfen ex Schweigg.) Rydb. -- not accepted
  Agropyron molle (Scribn. & J.G. Sm.) Rydb. -- not accepted
  Agropyron palmeri (Scribn. & J.G. Sm.) Rydb. -- not accepted
  Agropyron pseudorepens var. vulpinum (Rydb.) Boivin -- not accepted
  Agropyron smithii Rydb. -- not accepted
  Agropyron smithii var. smithii Rydb. -- not accepted
  Agropyron vulpinum (Rydb.) Hitchc. -- not accepted
  Agrostis atrata Rydb. -- not accepted
  Agrostis bakeri Rydb. -- not accepted
  Agrostis borealis var. bakeri (Rydb.) Koji Ito -- not accepted
  Agrostis idahoensis var. bakeri (Rydb.) W.A. Weber -- not accepted -- Baker's bentgrass
  Agrostis reptans Rydb. -- not accepted
  Agrostis variabilis Rydb. -- accepted -- mountain bentgrass, mountain redtop
  Agrostis variabilis auct. non Rydb. -- not accepted -- mountain bentgrass
  Aira alpicola (Rydb.) Rydb. -- not accepted
  Aira curtifolia (Scribn.) Rydb. -- not accepted
  Aira pungens (Rydb.) Rydb. -- not accepted
  Aira vaseyana Rydb. -- not accepted
  Aletes latiloba (Rydb.) W.A. Weber -- not accepted
  Aletes longiloba (Rydb.) W.A. Weber -- not accepted
  Aliciella haydenii ssp. crandallii (Rydb.) J.M. Porter -- not accepted
  Aliciella hutchinsifolia (Rydb.) J.M. Porter -- accepted -- desert pale gilia
  Aliciella subacaulis (Rydb.) J.M. Porter & L.A. Johnson -- accepted -- pinyon gilia
  Allionia bracteata Rydb. -- not accepted
  Allioniella oxybaphoides (A. Gray) Rydb. -- not accepted
  Allium aridum Rydb. -- not accepted
  Allium cernuum var. neomexicanum (Rydb.) J.F. Macbr. -- not accepted -- New Mexican nodding onion
  Allium fibrosum Rydb., non Regel -- not accepted
  Allium macropetalum Rydb. -- accepted -- largeflower onion, largeflower wild onion
  Allium natans Rydb. -- not accepted
  Allium neomexicanum Rydb. -- not accepted
  Allium recurvatum Rydb. -- not accepted
  Alnus sinuata (Regel) Rydb. -- not accepted
  Alsinanthe macrantha (Rydb.) W.A. Weber -- not accepted
  Alsine americana (Porter ex B.L. Rob.) Rydb. -- not accepted
  Alsine calycantha (Ledeb.) Rydb. -- not accepted
  Alsine palmeri Rydb. -- not accepted
  Alsine stricta (Richardson) Rydb. -- not accepted
  Alsinopsis obtusiloba Rydb. -- not accepted
  Alsinopsis rossii (R. Br. ex Richardson) Rydb. -- not accepted
  Amaranthus pubescens (Uline & W.L. Bray) Rydb. -- not accepted
  Amarella plebeja var. holmii (Wettst.) Rydb. -- not accepted
  Amarella strictiflora (Rydb.) Greene -- not accepted
  Amauriopsis Rydb. -- accepted
  Amauriopsis dissecta (A. Gray) Rydb. -- accepted -- ragleaf bahia
  Ambrosia californica Rydb. -- not accepted
  Ambrosia linearis (Rydb.) Payne -- accepted -- streaked bur ragweed, streaked burr ragweed
  Ambrosia monophylla (Walter) Rydb. -- not accepted
  Ambrosia psilostachya var. californica (Rydb.) S.F. Blake -- not accepted
  Ambrosia rugelii Rydb. -- not accepted
  Ambrosia salsola var. pentalepis (Rydb.) Strother & B.G. Baldw. -- not accepted
  Amorpha bushii Rydb. -- not accepted
  Amorpha crenulata Rydb. -- not accepted -- crenulate lead-plant
  Amorpha curtissii Rydb. -- not accepted
  Amorpha floridana Rydb. -- not accepted
  Amorpha herbacea var. crenulata (Rydb.) Isely -- accepted -- clusterspike false indigo, crenulate lead-plant
  Amorpha herbacea var. floridana (Rydb.) Wilbur -- not accepted
  Amorpha occidentalis var. arizonica (Rydb.) E.J. Palmer -- not accepted
  Amsinckia rugosa Rydb. -- not accepted
  Amsonia eastwoodiana Rydb. -- not accepted -- Eastwood's bluestar
  Androcera rostrata (Dunal) Rydb. -- not accepted
  Androsace occidentalis var. simplex (Rydb.) H. St. John -- not accepted
  Androsace puberulenta Rydb. -- not accepted
  Androsace septentrionalis ssp. puberulenta (Rydb.) G.T. Robbins -- not accepted -- pygmy-flower rock-jasmine, pygmyflower rockjasmine
  Androsace septentrionalis var. puberulenta (Rydb.) R. Knuth -- not accepted
  Anemone drummondii var. lithophila (Rydb.) C.L. Hitchc. -- accepted -- Little Belt Mountain thimbleweed
  Anemone lithophila Rydb. -- not accepted -- Little Belt Mountain thimbleweed
  Anemone piperi Britton ex Rydb. -- accepted -- Piper's anemone
  Anemone tuberosa Rydb. -- accepted -- desert windflower, tuber anemone
  Anemone tuberosa var. tuberosa Rydb. -- not accepted -- tuber anemone
  Antennaria acuta Rydb. -- not accepted
  Antennaria acuta Rydb. -- not accepted
  Antennaria albescens (E.E. Nelson) Rydb. -- not accepted
  Antennaria anaphaloides Rydb. -- accepted -- pearly pussytoes, pussytoes, tall everlasting
  Antennaria angustifolia Rydb. -- not accepted
  Antennaria angustifolia Ekman non Rydb. -- not accepted
  Antennaria arida var. humilis (Rydb.) E.E. Nelson -- not accepted
  Antennaria bracteosa Rydb. -- not accepted
  Antennaria campestris Rydb. -- not accepted
  Antennaria caroliniana Rydb. -- not accepted
  Antennaria flavescens Rydb. -- not accepted
  Antennaria foliacea var. humilis Rydb. -- not accepted
  Antennaria howellii var. campestris (Rydb.) B. Boivin -- not accepted
  Antennaria luzuloides var. oblanceolata (Rydb.) M. Peck -- not accepted
  Antennaria macrocephala (D.C. Eaton) Rydb. -- not accepted
  Antennaria microphylla Rydb. -- accepted -- littleleaf pussytoes, Rocky Mountain pussytoes, small leaf everlasting, smallleaf pussytoes
  Antennaria neglecta var. campestris (Rydb.) Steyerm. -- not accepted
  Antennaria oblanceolata Rydb. -- not accepted
  Antennaria parvifolia var. bracteosa (Rydb.) A. Nelson -- not accepted
  Antennaria piperi Rydb. -- not accepted
  Antennaria pulcherrima ssp. anaphaloides (Rydb.) W.A. Weber -- not accepted
  Antennaria pulcherrima var. anaphaloides (Rydb.) G.W. Douglas -- not accepted
  Antennaria rosea var. angustifolia (Rydb.) E.E. Nelson -- not accepted
  Antennaria rosulata Rydb. -- accepted -- Kaibab pussytoes
  Antennaria sierrae-blancae Rydb. -- not accepted
  Antennaria solitaria Rydb. -- accepted -- singlehead pussytoes
  Antennaria umbrinella Rydb. -- accepted -- brown everlasting, umber pussytoes
  Antennaria umbrinella auct. non Rydb. -- not accepted
  Antheropeas Rydb. -- accepted -- easter-bonnets, easterbonnets
  Antheropeas lanosum (A. Gray) Rydb. -- not accepted -- white easter-bonnets, white easterbonnets
  Antheropeas wallacei (A. Gray) Rydb. -- not accepted -- Wallace's woolydaisy, woolly easter-bonnets, woolly easterbonnets
  Anthopogon tonsum (Lunell) Rydb. -- not accepted
  Anticlea chlorantha (Richardson) Rydb. -- not accepted
  Anticlea coloradensis (Rydb.) Rydb. -- not accepted
  Anticlea elegans (Pursh) Rydb. -- accepted -- mountain deathcamas
  Anticlea elegans var. elegans (Pursh) Rydb. -- accepted -- mountain deathcamas
  Anticlea vaginata Rydb. -- accepted -- sheathed deathcamas
  Anticlea virescens (Kunth) Rydb. -- accepted -- green deathcamas
  Aphanes australis Rydb. -- accepted
  Aphanes occidentalis (Nutt.) Rydb. -- accepted
  Apinus albicaulis (Engelm.) Rydb. -- not accepted
  Apinus flexilis (E. James) Rydb. -- not accepted
  Apocynum scopulorum Greene ex Rydb. -- not accepted
  Aquilegia saximontana Rydb. -- accepted -- Rocky Mountain blue columbine
  Arabidopsis glauca (Nutt.) Rydb. -- not accepted
  Arabidopsis novae-angliae (Rydb.) Britton -- not accepted
  Arabidopsis richardsonii (Rydb.) Rydb. -- not accepted
  Arabis bourgovii Rydb. -- not accepted
  Arabis fendleri var. spatifolia (Rydb.) Rollins -- not accepted -- spoonleaf rockcress
  Arabis holboellii var. retrofracta (Graham) Rydb. -- not accepted -- a holboell rock-cress, second rockcress
  Arabis macdougalii Rydb. -- not accepted
  Arabis mcdougalii Rydb. -- not accepted
  Arabis selbyi Rydb. -- not accepted -- Selby's rockcress
  Aragallus argophyllus Rydb. -- not accepted
  Aragallus atropurpureus Rydb. -- not accepted
  Aragallus besseyi Rydb. -- not accepted
  Aragallus viscidulus Rydb. -- not accepted
  Aragallus viscidulus var. depressus Rydb. -- not accepted
  Arceuthobium cyanocarpum (A. Nelson ex Rydb.) A. Nelson -- not accepted -- limber pine dwarf mistletoe
  Arenaria confusa Rydb. -- not accepted
  Arenaria congesta var. cephaloidea (Rydb.) Maguire -- not accepted -- sharptip sandwort
  Arenaria congesta var. lithophila (Rydb.) Maguire -- not accepted -- loosehead sandwort, rock-loving sandwort
  Arenaria eastwoodiae Rydb. -- not accepted -- Eastwood's sandwort
  Arenaria eastwoodiae var. eastwoodiae Rydb. -- not accepted -- Eastwood's sandwort
  Arenaria fendleri var. eastwoodiae (Rydb.) H.D. Harr. -- not accepted
  Arenaria fendleri var. porteri Rydb. -- not accepted -- Porter's sandwort
  Arenaria fendleri var. tweedyi (Rydb.) Maguire -- not accepted -- Tweedy's sandwort
  Arenaria lithophila Rydb. -- not accepted
  Arenaria macrantha (Rydb.) A. Nelson -- not accepted
  Arenaria obtusiloba (Rydb.) Fernald -- not accepted
  Arenaria subcongesta (S. Watson) Rydb. -- not accepted
  Argemone munita ssp. rotundata (Rydb.) G.B. Ownbey -- accepted -- flatbud prickly poppy, flatbud pricklypoppy
  Argemone munita var. rotundata (Rydb.) Shinners -- not accepted
  Argemone rotundata Rydb. -- not accepted
  Argentina anserina (L.) Rydb. -- not accepted -- silverweed cinquefoil
  Argentina anserina var. concolor (Ser.) Rydb. -- not accepted
  Argentina argentea (L.) Rydb. -- not accepted
  Argentina egedii (Wormsk.) Rydb. -- not accepted -- Pacific silverweed
  Argentina egedii ssp. egedii (Wormsk.) Rydb. -- not accepted -- Pacific silverweed
  Argentina occidentalis Rydb. -- not accepted
  Argentina subarctica Rydb. -- not accepted
  Arnica amplexifolia Rydb. -- not accepted
  Arnica chandleri Rydb. -- not accepted
  Arnica cordifolia var. humilis (Rydb.) Maguire -- not accepted
  Arnica cordifolia var. pumila (Rydb.) Maguire -- not accepted
  Arnica cusickii Rydb. -- not accepted
  Arnica discoidea var. alata (Rydb.) Cronquist -- not accepted
  Arnica gracilis Rydb. -- accepted -- smallhead arnica
  Arnica humilis Rydb. -- not accepted
  Arnica latifolia var. gracilis (Rydb.) Cronquist -- not accepted
  Arnica louiseana var. brevifolia (Rydb.) Maguire -- not accepted
  Arnica louiseana var. illiamnae (Rydb.) Maguire -- not accepted
  Arnica louiseana var. mendenhallii (Rydb.) Maguire -- not accepted
  Arnica parviflora ssp. alata (Rydb.) Maguire -- not accepted
  Arnica spathulata ssp. eastwoodiae (Rydb.) Maguire -- not accepted
  Arnica spathulata var. eastwoodiae (Rydb.) Ediger & T.M. Barkley -- not accepted
  Artemisia alaskana Rydb. -- accepted -- Alaska wormwood
  Artemisia angusta Rydb. -- not accepted
  Artemisia angustifolia (Gray) Rydb. -- not accepted
  Artemisia arctica ssp. comata (Rydb.) Hultén -- not accepted -- boreal sagebrush
  Artemisia arctica ssp. saxicola (Rydb.) Hultén -- not accepted -- arctic wormwood
  Artemisia californica var. insularis (Rydb.) Munz -- not accepted
  Artemisia camporum Rydb. -- not accepted
  Artemisia candicans Rydb. -- not accepted
  Artemisia comata Rydb. -- not accepted
  Artemisia diversifolia Rydb. -- not accepted
  Artemisia elatior (Torr. & A. Gray) Rydb. -- not accepted
  Artemisia gormanii Rydb. -- not accepted
  Artemisia herriotii Rydb. -- not accepted
  Artemisia hyperborea Rydb. -- not accepted
  Artemisia ludoviciana ssp. candicans (Rydb.) D.D. Keck -- accepted -- gray sagewort, white sagebrush
  Artemisia ludoviciana ssp. sulcata (Rydb.) D.D. Keck -- accepted -- green sagewort, white sagebrush
  Artemisia ludoviciana var. brittonii (Rydb.) Fernald -- not accepted
  Artemisia neomexicana Greene ex Rydb. -- not accepted
  Artemisia norvegica var. comata (Rydb.) S.L. Welsh -- not accepted
  Artemisia pabularis (A. Nelson) Rydb. -- not accepted
  Artemisia ripicola Rydb. -- not accepted
  Artemisia sulcata Rydb. -- not accepted
  Artemisia tacomensis Rydb. -- not accepted
  Artemisia tilesii ssp. gormanii (Rydb.) Hultén -- not accepted -- Tilesius' wormwood
  Artemisia tridentata ssp. vaseyana (Rydb.) Beetle -- accepted -- big sagebrush, mountain big sagebrush
  Artemisia tridentata var. vaseyana (Rydb.) B. Boivin -- not accepted
  Artemisia tripartita Rydb. -- accepted -- threetip sagebrush
  Artemisia tripartita ssp. tripartita Rydb. -- accepted -- Idaho threetip sagebrush, threetip sagebrush
  Artemisia tyrellii Rydb. -- not accepted
  Artemisia unalaskensis Rydb. -- not accepted
  Artemisia vaseyana Rydb. -- not accepted
  Aruncus acuminatus Rydb. -- not accepted
  Aruncus allegheniensis Rydb. -- not accepted
  Aruncus allegheniensis var. pubescens (Rydb.) Fernald -- not accepted
  Aruncus dioicus var. acuminatus (Rydb.) H. Hara -- accepted -- bride's feathers
  Aruncus dioicus var. pubescens (Rydb.) Fernald -- accepted -- bride's feathers
  Aruncus pubescens Rydb. -- not accepted
  Aruncus sylvester ssp. acuminatus (Rydb.) Jeps. -- not accepted
  Aster apricus (A. Gray) Rydb. -- not accepted
  Aster batesii Rydb. -- not accepted
  Aster ciliolatus var. maccallae (Rydb.) A.G. Jones -- not accepted -- MacCall's aster
  Aster ciliolatus var. maccallii (Rydb.) A.G. Jones -- not accepted
  Aster ciliolatus var. wilsonii (Rydb.) A.G. Jones -- not accepted -- Wilson's aster
  Aster commutatus var. crassulus (Rydb.) S.F. Blake -- not accepted
  Aster commutatus var. polycephalus S.F. Blake, non Aster polycephalus Rydb. -- not accepted
  Aster crassulus Rydb. -- not accepted
  Aster exiguus Rydb. -- not accepted
  Aster falcatus var. crassulus (Rydb.) Cronquist -- not accepted -- rough white prairie aster
  Aster finkii Rydb. -- not accepted
  Aster franklinianus Rydb. -- not accepted
  Aster junciformis Rydb. -- not accepted
  Aster juniperinus Rydb. -- not accepted
  Aster maccallae Rydb. -- not accepted
  Aster maccallii Rydb. -- not accepted
  Aster macounii Rydb. -- not accepted
  Aster mearnsii Rydb. -- not accepted
  Aster mollis Rydb. -- not accepted -- soft aster
  Aster osterhoutii Rydb. -- not accepted
  Aster phyllodes Rydb. -- not accepted
  Aster polycephalus Rydb. -- not accepted
  Aster stricticaulis (Torr. & A. Gray) Rydb. -- not accepted
  Aster subgriseus Rydb. -- not accepted
  Aster tweedyi Rydb. -- not accepted
  Aster wilsonii Rydb. -- not accepted
  Aster woldenii Rydb. -- not accepted
  Aster X batesii Rydb. (pro sp.) -- not accepted -- Bates' aster
  Aster X woldenii Rydb. (pro sp.) -- not accepted -- Wolden's aster
  Astragalus aboriginorum var. glabriusculus (Hook.) Rydb. -- not accepted
  Astragalus alpinus var. alpiniformis (Rydb.) M. Peck -- not accepted
  Astragalus amblyodon Kearney ex Rydb. -- not accepted
  Astragalus amphioxys var. melancalyx (Rydb.) Tidestr. -- not accepted
  Astragalus amphioxys var. melanocalyx (Rydb.) Tidestr. -- not accepted
  Astragalus arrectus var. kelseyi (Rydb.) M.E. Jones -- not accepted
  Astragalus bigelovii var. marcidus (Greene ex Rydb.) Isely -- not accepted
  Astragalus blyae (Rose ex Rydb.) Tidestr. -- not accepted
  Astragalus brevidens (Gand.) Rydb. -- not accepted
  Astragalus calycosus var. mancus (Rydb.) Barneby -- accepted -- defective milkvetch
  Astragalus calycosus var. monophyllidius (Rydb.) Barneby -- accepted -- one-leaf milkvetch, Torrey's milkvetch
  Astragalus canovirens (Rydb.) Barneby -- not accepted
  Astragalus cinerascens (Rydb.) Tidestr. -- not accepted
  Astragalus collieri (Rydb.) A.E. Porsild -- not accepted
  Astragalus collinus var. laurentii (Rydb.) Barneby -- accepted -- Laurent's milkvetch
  Astragalus conjunctus var. sheldonii (Rydb.) M. Peck -- not accepted
  Astragalus crotalariae var. davidsonii (Rydb.) Munz & McBurney -- not accepted
  Astragalus curvicarpus var. subglaber (Rydb.) Barneby -- accepted -- smooth loco milkvetch
  Astragalus datilensis (Rydb.) Tidestr. -- not accepted
  Astragalus deanei (Rydb.) Barneby -- accepted -- Deane's milk-vetch
  Astragalus decumbens var. oblongifolius (Rydb.) Cronquist -- not accepted
  Astragalus didymocarpus var. milesianus (Rydb.) Jeps. -- accepted -- dwarf white milkvetch, Miles milkvetch
  Astragalus didymocarpus var. obispensis (Rydb.) Jeps. -- accepted -- San Obispo milkvetch
  Astragalus didymocarpus var. obispoensis (Rydb.) Jeps. -- not accepted
  Astragalus douglasii var. megalophysus (Rydb.) Munz & McBurney -- not accepted
  Astragalus douglasii var. perstrictus (Rydb.) Munz & McBurney -- accepted -- campo milkvetch, Jacumba milk-vetch
  Astragalus earlei Greene ex Rydb. -- not accepted
  Astragalus egglestonii (Rydb.) Kearney & Peebles -- accepted -- Eggleston's milkvetch
  Astragalus emoryanus (Rydb.) Cory -- accepted -- Emory's milkvetch
  Astragalus emoryanus var. emoryanus (Rydb.) Cory -- accepted -- Emory's milkvetch
  Astragalus eucosmus var. fernaldii (Rydb.) B. Boivin -- not accepted
  Astragalus fernaldii (Rydb.) H.F. Lewis -- not accepted
  Astragalus flexuosus var. sierrae-blancae (Rydb.) Barneby -- not accepted
  Astragalus flexuosus var. sierraeblancae (Rydb.) Barneby -- not accepted
  Astragalus forwoodii var. wallowensis (Rydb.) M. Peck -- not accepted
  Astragalus halei Rydb. -- not accepted
  Astragalus harringtonii (Rydb.) Coville & Standl. ex Hultén -- not accepted
  Astragalus humistratus var. humivagans (Rydb.) Barneby -- accepted -- groundcover milkvetch
  Astragalus incurvus (Rydb.) Abrams -- not accepted
  Astragalus iodopetalus (Rydb.) Barneby -- accepted -- violet milkvetch
  Astragalus lagopinus (Rydb.) M. Peck -- not accepted
  Astragalus laurentii (Rydb.) M. Peck -- not accepted
  Astragalus lentiginosus var. kennedyi (Rydb.) Barneby -- accepted -- Kennedy's milkvetch
  Astragalus lentiginosus var. macrolobus (Rydb.) Barneby -- accepted -- West Humboldt milkvetch
  Astragalus lentiginosus var. platyphyllidius (Rydb.) M. Peck -- accepted -- broad-leaved milkvetch
  Astragalus lentiginosus var. sesquimetralis (Rydb.) Barneby -- accepted -- Mono locoweed, Sodaville milk-vetch, Sodaville milkvetch
  Astragalus lentiginosus var. stramineus (Rydb.) Barneby -- accepted -- freckled milkvetch, straw milkvetch
  Astragalus linearis (Rydb.) A.E. Porsild -- not accepted
  Astragalus longifolius (Pursh) Rydb. -- not accepted
  Astragalus macgregorii (Rydb.) Tidestr. -- not accepted
  Astragalus macounii Rydb. -- not accepted
  Astragalus magdalenae var. niveus (Rydb.) Barneby -- accepted
  Astragalus marianus (Rydb.) Barneby -- not accepted
  Astragalus minthorniae (Rydb.) Jeps. -- accepted -- Minthorn's milkvetch
  Astragalus minthorniae var. minthorniae (Rydb.) Jeps. -- accepted -- Minthorn's milkvetch
  Astragalus miser var. hylophilus (Rydb.) Barneby -- accepted -- woody milkvetch
  Astragalus miser var. oblongifolius (Rydb.) Cronquist -- accepted -- timber milkvetch
  Astragalus mollissimus var. earlei (Greene ex Rydb.) Tidestr. -- accepted -- Earle's woolly locoweed, Earle's woolly milkvetch, woolly locoweed
  Astragalus mollissimus var. marcidus (Greene ex Rydb.) Barneby -- accepted -- Davis Mountains locoweed, withered wooly milk-vetch, woolly locoweed, woolly milkvetch
  Astragalus newberryi var. blyae (Rose ex Rydb.) Barneby -- accepted -- Bly milkvetch, Newberry's milkvetch
  Astragalus niveus Rydb. -- not accepted
  Astragalus nuttallianus var. imperfectus (Rydb.) Barneby -- accepted -- imperfect milkvetch, turkey peas, turkeypeas
  Astragalus pachystachys Rydb. -- not accepted
  Astragalus pardalinus (Rydb.) Barneby -- accepted -- panther milkvetch
  Astragalus parishii ssp. perstrictus (Rydb.) Abrams -- not accepted
  Astragalus paysonii (Rydb.) Barneby -- accepted -- Payson's milkvetch
  Astragalus praelongus var. ellisiae (Rydb.) Barneby ex B.L. Turner -- accepted -- Ellis' stinking milkvetch
  Astragalus proximus (Rydb.) Wooton & Standl. -- accepted -- Aztec milkvetch
  Astragalus purshii var. lagopinus (Rydb.) Barneby -- accepted -- hare's-foot milkvetch, woollypod milkvetch
  Astragalus pycnostachyus var. lanosissimus (Rydb.) Munz & McBurney -- accepted -- marsh milkvetch, Ventura marsh milk-vetch
  Astragalus recedens (Greene ex Rydb.) Ced. Porter -- not accepted
  Astragalus reventiformis (Rydb.) Barneby -- accepted -- Yakima milkvetch
  Astragalus reventus var. sheldonii (Rydb.) C.L. Hitchc. -- not accepted
  Astragalus robbinsii ssp. harringtonii (Rydb.) Hultén -- not accepted
  Astragalus robbinsii var. alpiniformis (Rydb.) Barneby ex C.L. Hitchc. -- accepted -- Robbins milk-vetch, Robbins' milkvetch
  Astragalus robbinsii var. fernaldii (Rydb.) Barneby -- accepted -- astragale de Robbins variété de Fernald, Fernald's milk-vetch, Fernald's milkvetch
  Astragalus robbinsii var. harringtonii (Rydb.) Barneby -- accepted -- Harold's milkvetch
  Astragalus scaphoides (M.E. Jones) Rydb. -- accepted -- bitterroot milkvetch
  Astragalus sheldonii (Rydb.) Barneby -- accepted -- Sheldon's milkvetch
  Astragalus spatulatus var. uniflorus (Rydb.) Barneby -- not accepted
  Astragalus stictocarpus (Rydb.) Tidestr. -- not accepted
  Astragalus subglaber (Rydb.) M. Peck -- not accepted
  Astragalus sulphurescens Rydb. -- not accepted
  Astragalus tehachapiensis (Rydb.) Tidestr. -- not accepted
  Astragalus tehatchapiensis (Rydb.) Tidestr. -- not accepted
  Astragalus tenellus var. strigulosus (Rydb.) F.J. Herm. -- not accepted
  Astragalus tetrapterus var. cinerascens (Rydb.) Barneby -- not accepted
  Astragalus tidestromii (Rydb.) Clokey -- accepted -- Tidestrom's milkvetch
  Astragalus ventosus Suksd. ex Rydb. -- not accepted
  Astragalus ventrosus Suksd. ex Rydb. -- not accepted
  Astragalus whitneyi ssp. siskiyouensis (Rydb.) Abrams -- not accepted
  Astragalus whitneyi var. lenophyllus (Rydb.) Barneby -- accepted -- balloon pod milkvetch, balloonpod milkvetch
  Astragalus whitneyi var. siskiyouensis (Rydb.) Barneby -- accepted -- Siskiyou milkvetch
  Astragalus williamsii Rydb. -- accepted -- Williams' milkvetch
  Atelophragma aboriginorum (Richardson) Rydb. -- not accepted
  Atelophragma alpiniforme Rydb. -- not accepted
  Atelophragma alpinum (L.) Rydb. -- not accepted
  Atelophragma elegans (Hook.) Rydb. -- not accepted
  Atelophragma harringtonii Rydb. -- not accepted
  Atenia montana (Blank.) Rydb. -- not accepted
  Atriplex buxifolia Rydb. -- not accepted
  Atriplex canescens ssp. garrettii (Rydb.) H.M. Hall & Clem. -- not accepted
  Atriplex canescens var. garrettii (Rydb.) L.D. Benson -- not accepted
  Atriplex garrettii Rydb. -- accepted -- Garrett's saltbush
  Atriplex garrettii var. garrettii Rydb. -- accepted -- Garrett's saltbush
  Atriplex nuttallii ssp. buxifolia (Rydb.) H.M. Hall & Clem. -- not accepted
  Atriplex subconferta Rydb. -- not accepted
  Atriplex subspicata (Nutt.) Rydb. -- not accepted -- halberdleaf orach, orach saltbush, saline saltbush, spearscale, spreading orach
  Atriplex suckleyi (Torr.) Rydb. -- not accepted -- Suckley's orach
  Atriplex tetraptera (Benth.) Rydb. -- not accepted
  Atriplex X odontoptera Rydb. (pro. sp.) -- accepted
  Azaleastrum albiflorum (Hook.) Rydb. -- not accepted
  Baileya multiradiata var. thurberi (Rydb.) Kittell -- not accepted
  Baileya perennis (A. Nelson) Rydb. -- not accepted
  Balsamorhiza X tomentosa Rydb. (pro sp.) -- accepted -- tomentose balsamroot
  Baptisia vespertina Small ex Rydb. -- not accepted
  Barbarea americana Rydb. -- not accepted
  Batidophaca lotiflora (Hook.) Rydb. -- not accepted
  Batidophaca lotiflorus (Hook.) Rydb. -- not accepted
  Benthamantha glabella (A. Gray) Rydb. -- not accepted
  Berthelotia sericea (Nutt.) Rydb. -- not accepted
  Besseya Rydb. -- not accepted -- kittentail
  Besseya alpina (A. Gray) Rydb. -- not accepted -- alpine besseya
  Besseya bullii (Eaton) Rydb. -- not accepted -- Bull's coraldrops
  Besseya plantaginea (E. James) Rydb. -- not accepted -- White River coraldrops
  Besseya ritteriana (Eastw.) Rydb. -- not accepted -- Ritter's coraldrops
  Besseya rubra (Douglas ex Hook.) Rydb. -- not accepted -- red besseya, red kittentail
  Besseya wyomingensis (A. Nelson) Rydb. -- not accepted -- Wyoming besseya, Wyoming kittentail
  Betula papyrifera var. subcordata (Rydb.) Sarg. -- not accepted
  Bidens puberula (Wiegand) Rydb. -- not accepted
  Blephariglotis blephariglottis (Willd.) Rydb. -- not accepted
  Blephariglotis ciliaris (L.) Rydb. -- not accepted
  Blephariglotis grandiflora (Bigelow) Rydb. -- not accepted
  Blephariglotis peramoena (A. Gray) Rydb. -- not accepted
  Blephariglotis psycodes (L.) Rydb. -- not accepted
  Blephariglottis blephariglottis (Willd.) Rydb. -- not accepted
  Blephariglottis ciliaris (L.) Rydb. -- not accepted
  Blephariglottis grandiflora (Bigelow) Rydb. -- not accepted
  Blephariglottis peramoena (A. Gray) Rydb. -- not accepted
  Blephariglottis psycodes (L.) Rydb. -- not accepted
  Blitum hastatum Rydb. -- not accepted
  Boebera papposa (Vent.) Rydb. ex Britton -- not accepted
  Boechera fendleri var. spatifolia (Rydb.) W.A. Weber -- not accepted
  Boechera selbyi (Rydb.) W.A. Weber -- not accepted
  Boechera spatifolia (Rydb.) Windham & Al-Shehbaz -- accepted -- spoonleaf rockcress
  Boisduvalia salicina (Nutt. ex Torr. & A. Gray) Rydb. -- not accepted
  Bothriochloa saccharoides (Sw.) Rydb. -- accepted -- silver bluestem
  Bothriochloa saccharoides ssp. saccharoides (Sw.) Rydb. -- not accepted
  Bothriochloa saccharoides var. saccharoides (Sw.) Rydb. -- accepted
  Boykinia heucheriformis (Rydb.) Rosend. -- not accepted -- alumroot brookfoam
  Boykinia jamesii var. heucheriformis (Rydb.) Engl. -- not accepted
  Boykinia turbinata (Rydb.) Fedde -- not accepted
  Boykinia vancouverensis (Rydb.) Fedde -- not accepted
  Braya humilis ssp. richardsonii (Rydb.) Hultén -- not accepted
  Braya humilis var. novae-angliae (Rydb.) Fernald -- not accepted
  Braya novae-angliae (Rydb.) T.J. Sřrensen -- not accepted
  Braya richardsonii (Rydb.) Fernald -- not accepted
  Bromus ciliatus var. porteri (J.M. Coult.) Rydb. -- not accepted
  Bromus flodmanii Rydb. -- not accepted
  Bromus lanatipes (Shear) Rydb. -- accepted -- woolly brome
  Bromus latior (Shear) Rydb. -- not accepted
  Bromus paniculatus (Shear) Rydb. -- not accepted
  Calamagrostis canadensis var. acuminata Vasey ex Shear & Rydb. -- not accepted
  Calamagrostis elongata (Kearney) Rydb. -- not accepted
  Calamagrostis langsdorfii var. acuminata (Vasey ex Shear & Rydb.) Litw. -- not accepted
  Calamagrostis luxurians (Kearney) Rydb. -- not accepted
  Calyptridium pygmaeum Parish ex Rydb. -- not accepted
  Campanula aparinoides var. uliginosa (Rydb.) Gleason -- not accepted
  Campanula uliginosa Rydb. -- not accepted
  Capnoides brachycarpum Rydb. -- not accepted
  Capnoides hastatum Rydb. -- not accepted
  Cardamine unijuga Rydb. -- not accepted
  Carduus americanus (A. Gray) Rydb. -- not accepted
  Carduus coloradensis Rydb. -- not accepted
  Carduus tracyi Rydb. -- not accepted
  Carex aquatilis ssp. altior (Rydb.) Hultén -- not accepted
  Carex aquatilis var. altior (Rydb.) Fernald -- not accepted
  Carex ebenea Rydb. -- accepted -- ebony sedge
  Carex praticola Rydb. -- accepted -- meadow sedge, northern meadow sedge
  Carex pseudoscirpoidea Rydb. -- not accepted -- western singlespike sedge
  Carex scirpoidea ssp. pseudoscirpoidea (Rydb.) Dunlop -- accepted -- western singlespike sedge
  Carex scirpoidea var. pseudoscirpoidea (Rydb.) Cronquist -- not accepted
  Caryopitys monophylla (Torr. & Frém.) Rydb. -- not accepted
  Castilleja applegatei var. viscida (Rydb.) Ownbey -- not accepted
  Castilleja crista-galli Rydb. -- accepted -- mountainside Indian paintbrush
  Castilleja gracillima Rydb. -- not accepted
  Castilleja leonardii Rydb. -- not accepted
  Castilleja linearis Rydb. -- not accepted
  Castilleja luteovirens Rydb. -- not accepted
  Castilleja lutescens (Greenm.) Rydb. -- accepted -- stiff yellow Indian paintbrush
  Castilleja parvula Rydb. -- accepted -- Tushar Indian paintbrush, Tushar Plateau Indian paintbrush
  Castilleja pilosa (S. Watson) Rydb. -- accepted -- hairy paintbrush, parrothead Indian paintbrush
  Castilleja pilosa var. pilosa (S. Watson) Rydb. -- accepted -- parrothead Indian paintbrush
  Castilleja puberula Rydb. -- accepted -- shortflower Indian paintbrush
  Castilleja pulchella Rydb. -- accepted -- beautiful Indian paintbrush
  Castilleja rhexiifolia Rydb. -- accepted -- rhexialeaf paintbrush, splitleaf Indian paintbrush
  Castilleja rhexiifolia var. sulphurea (Rydb.) N.D. Atwood -- not accepted
  Castilleja sulphurea Rydb. -- accepted -- sulphur Indian paintbrush
  Castilleja viscida Rydb. -- not accepted
  Caulanthus glaber (M.E. Jones) Rydb. -- not accepted
  Caulanthus lasiophyllus var. utahensis (Rydb.) Payson -- not accepted
  Ceanothus pubescens (Torr. & A. Gray ex S. Watson) Rydb. ex Small -- not accepted
  Ceanothus subsericeus Rydb. -- not accepted
  Cerastium beeringianum ssp. earlei (Rydb.) Hultén -- not accepted -- Bering chickweed
  Cerastium earlei Rydb. -- not accepted
  Cerastium graminifolium Rydb. -- not accepted
  Cerastium pulchellum Rydb. -- not accepted
  Cerastium thermale Rydb. -- not accepted
  Ceratoides lanata var. subspinosa (Rydb.) J.T. Howell -- not accepted
  Ceratoxalis coloradensis (Rydb.) Lunell -- not accepted
  Cercocarpus alnifolius Rydb. -- not accepted
  Cercocarpus argenteus Rydb. -- not accepted
  Cercocarpus betuloides ssp. macrourus (Rydb.) A.E. Murray -- not accepted
  Cercocarpus betuloides var. macrourus (Rydb.) Jeps. -- accepted -- Klamath mountain-mahogany
  Cercocarpus douglasii Rydb. -- not accepted
  Cercocarpus eximius (C.K. Schneid.) Rydb. -- not accepted
  Cercocarpus hypoleucus Rydb. -- not accepted
  Cercocarpus ledifolius var. hypoleucus (Rydb.) M. Peck -- not accepted
  Cercocarpus macrourus Rydb. -- not accepted
  Cercocarpus montanus var. argenteus (Rydb.) F.L. Martin -- not accepted -- silver birchleaf mountain-mahogany, silver mountain-mahogany
  Cercocarpus montanus var. flabellifolius (Rydb.) Kearney & Peebles -- not accepted
  Cercocarpus montanus var. macrourus (Rydb.) F.L. Martin -- not accepted -- Klamath mountain-mahogany
  Cercocarpus rotundifolius Rydb. -- not accepted
  Chaenactis douglasii var. rubricaulis (Rydb.) Ferris -- not accepted
  Chaenactis humilis Rydb. -- not accepted
  Chaenactis rubricaulis Rydb. -- not accepted
  Chamaechaenactis Rydb. -- accepted -- chamaechaenactis
  Chamaechaenactis scaposa (Eastw.) Rydb. -- accepted -- fullstem
  Chamaechaenactis scaposa var. scaposa (Eastw.) Rydb. -- not accepted -- fullstem
  Chamaepericlymenum unalaschkense (Ledeb.) Rydb. -- not accepted
  Chamaerhodos erecta ssp. nuttallii (Pickering ex Rydb.) Hultén -- not accepted -- chamaerhodos, little-rose, Nuttall's little rose
  Chamaerhodos nuttallii Pickering ex Rydb. -- not accepted
  Chamaesaracha crenata Rydb. -- accepted -- toothed five eyes
  Chamaesaracha villosa Rydb. -- accepted -- Trans-Pecos five eyes
  Chamaesyce albicaulis (Rydb.) Rydb. -- not accepted
  Chamaesyce exstipulata (Engelm.) Rydb. -- not accepted
  Chamaesyce flagelliformis (Engelm.) Rydb. -- not accepted
  Chamaesyce greenei (Millsp.) Rydb. -- not accepted
  Chamaesyce parryi (Engelm.) Rydb. -- not accepted -- Parry's sandmat, Parry's spurge
  Chamaesyce rugulosa (Engelm. ex Millsp.) Rydb. -- not accepted
  Chamerion subdentatum (Rydb.) Á. Löve & D. Löve -- not accepted
  Chamomilla chamomilla (L.) Rydb. -- not accepted
  Chamomilla maritima (L.) Rydb. -- not accepted
  Chamomilla occidentalis (Greene) Rydb. -- not accepted
  Chamomilla suaveolens (Pursh) Rydb. -- not accepted
  Cheirinia inconspicua (S. Watson) Rydb. -- not accepted
  Chenopodium atrovirens Rydb. -- accepted -- dark goosefoot, pinyon goosefoot
  Chenopodium fremontii var. atrovirens (Rydb.) Fosberg -- not accepted
  Chenopodium oblongifolium (S. Watson) Rydb. -- not accepted
  Chenopodium pratericola Rydb. -- accepted -- desert goosefoot
  Chenopodium wolfii Rydb. -- not accepted
  Chimaphila maculata var. dasystemma (Torr. ex Rydb.) Kearney & Peebles -- not accepted
  Chimaphila occidentalis Rydb. -- not accepted
  Chimaphila umbellata ssp. acuta (Rydb.) Hultén -- accepted -- pipsissewa
  Chimaphila umbellata ssp. occidentalis (Rydb.) Hultén -- accepted -- pipsissewa
  Chimaphila umbellata var. acuta (Rydb.) S.F. Blake -- not accepted
  Chimaphila umbellata var. occidentalis (Rydb.) S.F. Blake -- not accepted
  Chlorocrambe Rydb. -- accepted
  Chlorocrambe hastata (S. Watson) Rydb. -- accepted -- spearhead
  Chorisiva Rydb. -- accepted
  Chorisiva nevadensis (M.E. Jones) Rydb. -- accepted -- Nevada sumpweed
  Chorizanthe brevicornu ssp. spathulata (Small ex Rydb.) Munz -- not accepted
  Chorizanthe brevicornu var. spathulata (Small ex Rydb.) C.L. Hitchc. -- accepted -- brittle spineflower
  Chorizanthe spathulata Small ex Rydb. -- not accepted
  Chrysobotrya aurea (Pursh) Rydb. -- not accepted
  Chrysopsis alpicola Rydb. -- not accepted
  Chrysopsis amplifolia Rydb. -- not accepted
  Chrysopsis angustifolia Rydb. -- not accepted
  Chrysopsis ballardii Rydb. -- not accepted
  Chrysopsis barbata Rydb. -- not accepted
  Chrysopsis butleri Rydb. -- not accepted
  Chrysopsis caudata Rydb. -- not accepted
  Chrysopsis depressa Rydb. -- not accepted
  Chrysopsis horrida Rydb. -- not accepted
  Chrysopsis villosa var. angustifolia (Rydb.) Cronquist -- not accepted
  Chrysosplenium alternifolium ssp. iowense (Rydb.) Hultén -- not accepted
  Chrysosplenium alternifolium var. iowense (Rydb.) B. Boivin -- not accepted
  Chrysosplenium iowense Rydb. -- accepted -- Iowa golden saxifrage
  Chrysothamnus greenei ssp. filifolius (Rydb.) H.M. Hall & Clem. -- not accepted
  Chrysothamnus greenei var. filifolius (Rydb.) S.F. Blake -- not accepted
  Chrysothamnus nauseosus ssp. salicifolius (Rydb.) H.M. Hall & Clem. -- not accepted
  Chrysothamnus nauseosus var. albicaulis (Nutt.) Rydb. -- not accepted
  Chrysothamnus nauseosus var. salicifolius (Rydb.) H.M. Hall -- not accepted
  Cirsium acaulescens (Rydb.) K. Schum. -- not accepted
  Cirsium araneans Rydb. -- not accepted -- jeweled thistle
  Cirsium bipinnatum (Eastw.) Rydb. -- not accepted
  Cirsium butleri (Rydb.) Petr. -- not accepted
  Cirsium canovirens (Rydb.) Petr. -- not accepted -- graygreen thistle
  Cirsium centaureae (Rydb.) K. Schum. -- not accepted
  Cirsium clavatum var. osterhoutii (Rydb.) D.J. Keil -- accepted -- jeweled thistle, Osterhout's thistle
  Cirsium coloradense (Rydb.) Cockerell -- not accepted
  Cirsium coloradense ssp. acaulescens (Rydb.) Petr. -- not accepted
  Cirsium cymosum var. canovirens (Rydb.) D.J. Keil -- accepted -- graygreen thistle
  Cirsium diffusum (Eastw.) Rydb. -- not accepted
  Cirsium drummondii var. acaulescens (Rydb.) J.F. Macbr. -- not accepted
  Cirsium engelmannii Rydb. -- accepted -- Engelmann's thistle
  Cirsium erosum (Rydb.) K. Schum. -- not accepted
  Cirsium floccosum (Rydb.) Petr. -- not accepted
  Cirsium flodmanii (Rydb.) Arthur -- accepted -- Flodman's thistle
  Cirsium griseum (Rydb.) K. Schum. -- not accepted -- gray thistle
  Cirsium humboldtense Rydb. -- not accepted -- Humboldt County thistle
  Cirsium kelseyi (Rydb.) Petr. -- not accepted
  Cirsium lacerum (Rydb.) Petr. -- not accepted
  Cirsium lactucinum Rydb. -- not accepted
  Cirsium macounii (Greene) Rydb. -- not accepted
  Cirsium oblanceolatum (Rydb.) K. Schum. -- not accepted
  Cirsium olivescens (Rydb.) Petr. -- not accepted -- summer thistle
  Cirsium oreophilum (Rydb.) K. Schum. -- not accepted -- crow thistle
  Cirsium osterhoutii (Rydb.) Petr. -- not accepted -- Osterhout's thistle
  Cirsium perplexans (Rydb.) Petr. -- accepted -- Rocky Mountain thistle, spring thistle
  Cirsium plattense (Rydb.) Cockerell ex Daniels -- not accepted
  Cirsium polyphyllum (Rydb.) Petr. -- not accepted
  Cirsium pulcherrimum (Rydb.) K. Schum. -- accepted -- Wyoming thistle
  Cirsium pulcherrimum var. pulcherrimum (Rydb.) K. Schum. -- accepted -- Wyoming thistle
  Cirsium scariosum var. coloradense (Rydb.) D.J. Keil -- accepted -- Colorado thistle, glory thistle, summer thistle
  Cirsium spathulifolium Rydb. -- not accepted
  Cirsium subniveum Rydb. -- not accepted -- gray thistle, Jackson Hole thistle
  Cirsium tioganum var. coloradense (Rydb.) Dorn -- not accepted -- Colorado thistle, stemless thistle
  Cirsium tracyi (Rydb.) Petr. -- accepted -- Tracy's thistle
  Cirsium tweedyi (Rydb.) Petr. -- not accepted
  Cirsium tweedyi auct. non (Rydb.) Petr. -- not accepted
  Cirsium undulatum var. tracyi (Rydb.) S.L. Welsh -- not accepted -- gray thistle, Tracy's thistle, wavyleaf thistle
  Cirsium X erosum (Rydb.) K. Schum. (pro sp.) -- not accepted -- glory thistle
  Cistanthe pygmaea (Parish ex Rydb.) Hershk. -- accepted -- pygmy pussypaws
  Claytonia bellidifolia Rydb. -- not accepted
  Claytonia lanceolata var. multiscapa (Rydb.) C.L. Hitchc. -- not accepted -- lanceleaf springbeauty
  Claytonia lanceolata var. rosea (Rydb.) R.J. Davis -- not accepted
  Claytonia megarhiza var. bellidiflora (Rydb.) C.L. Hitchc. -- not accepted
  Claytonia megarhiza var. bellidifolia (Rydb.) C.L. Hitchc. -- not accepted -- alpine springbeauty
  Claytonia multiscapa Rydb. -- accepted -- lanceleaf springbeauty
  Claytonia multiscapa ssp. multiscapa Rydb. -- accepted -- lanceleaf springbeauty
  Claytonia parviflora ssp. utahensis (Rydb.) John M. Mill. & K.L. Chambers -- accepted -- streambank springbeauty
  Claytonia perfoliata ssp. mexicana (Rydb.) John M. Mill. & K.L. Chambers -- accepted -- miner's lettuce
  Claytonia perfoliata ssp. perfoliata var. utahensis (Rydb.) Poelln. -- not accepted
  Claytonia perfoliata var. utahensis (Rydb.) Poelln. -- not accepted
  Claytonia robusta (Somes) Rydb. -- not accepted
  Claytonia rosea Rydb. -- accepted -- western springbeauty
  Clematis occidentalis ssp. grosseserrata (Rydb.) Roy L. Taylor & MacBryde -- not accepted
  Clematis occidentalis var. grosseserrata (Rydb.) J.S. Pringle -- accepted -- western blue virginsbower
  Clematis versicolor Small ex Rydb. -- accepted -- manycolored virginsbower, pale leather flower
  Clematis virginiana var. missouriensis (Rydb.) E.J. Palmer & Steyerm. -- not accepted
  Cleomella cornuta Rydb. -- not accepted
  Clistoyucca brevifolia (Engelm.) Rydb. -- not accepted
  Cnemidophacos knowlesianus Rydb. -- not accepted
  Cnemidophacos pectinatus (Douglas ex Hook.) Rydb. -- not accepted
  Cnicus drummondii var. acaulescens Rydb. -- not accepted
  Collinsia parvula Rydb. -- not accepted
  Comandra californica Eastw. ex Rydb. -- not accepted
  Comandra umbellata ssp. californica (Eastw. ex Rydb.) Piehl -- accepted -- bastard toadflax, California bastard toadflax
  Comandra umbellata var. californica (Eastw. ex Rydb.) C.L. Hitchc. -- not accepted
  Comarella multifoliolata (Torr.) Rydb. -- not accepted
  Comarella sabulosa (M.E. Jones) Rydb. -- not accepted
  Conimitella Rydb. -- accepted
  Conimitella williamsii (D.C. Eaton) Rydb. -- accepted -- Williams' miterwort
  Corallorhiza ochroleuca Rydb. -- not accepted
  Corallorhiza striata var. ochroleuca (Rydb.) Magrath -- not accepted
  Corallorhiza striata var. vreelandii (Rydb.) L.O. Williams -- accepted -- Vreeland's coralroot
  Corallorrhiza ochroleuca Rydb. -- not accepted
  Corallorrhiza striata var. ochroleuca (Rydb.) Magrath -- not accepted
  Corallorrhiza striata var. vreelandii (Rydb.) L.O. Williams -- not accepted -- hooded coralroot, Vreeland's coralroot
  Coriflora versicolor (Small ex Rydb.) W.A. Weber -- not accepted
  Coriospermum villosum Rydb. -- not accepted
  Corispermum emarginatum Rydb. -- not accepted
  Corispermum hyssopifolium var. emarginatum (Rydb.) B. Boivin -- not accepted
  Corispermum marginale Rydb. -- not accepted
  Corispermum orientale var. emarginatum (Rydb.) J.F. Macbr. -- not accepted
  Corispermum villosum Rydb. -- accepted -- hairy bugseed
  Cornella canadensis (L.) Rydb. -- not accepted
  Cornella suecica (L.) Rydb. -- not accepted
  Cornus alba var. interior (Rydb.) B. Boivin -- not accepted
  Cornus interior (Rydb.) N. Petersen -- not accepted
  Cornus sericea var. interior (Rydb.) H. St. John -- not accepted
  Cornus stolonifera var. interior (Rydb.) H. St. John -- not accepted
  Corydalis caseana ssp. brachycarpa (Rydb.) G.B. Ownbey -- accepted -- Sierra fumewort
  Corydalis caseana ssp. hastata (Rydb.) G.B. Ownbey -- accepted -- Sierra fumewort
  Corydalis caseana var. hastata (Rydb.) C.L. Hitchc. -- not accepted
  Coryphantha radiosa (Engelm.) Rydb. -- not accepted
  Cracca carpenteri Rydb. -- not accepted
  Cracca curtissii Small ex Rydb. -- not accepted
  Cracca mohrii Rydb. -- not accepted
  Cracca texana Rydb. -- not accepted
  Cracca thurberi Rydb. -- not accepted
  Crepis alpicola (Rydb.) A. Nelson -- not accepted
  Crepis glaucella Rydb. -- not accepted
  Crepis occidentalis ssp. pumila (Rydb.) Babc. & Stebbins -- accepted -- largeflower hawksbeard
  Crepis occidentalis var. pumila (Rydb.) Babc. & Stebbins -- not accepted
  Crepis perplexans Rydb. -- not accepted
  Crepis runcinata ssp. hispidulosa (Howell ex Rydb.) Babc. & Stebbins -- accepted -- fiddleleaf hawksbeard
  Crepis runcinata var. hispidulosa Howell ex Rydb. -- not accepted
  Croptilon hookerianum var. validum (Rydb.) E.B. Sm. -- accepted -- Hooker's scratchdaisy
  Crunocallis chamissoi (Ledeb. ex Spreng.) Rydb. -- not accepted
  Cryptantha calycosa (A. Gray) Rydb. -- not accepted
  Cryptantha cinerea var. pustulosa (Rydb.) Higgins -- accepted -- James' catseye, James' cryptantha
  Cryptantha grandiflora Rydb. -- not accepted
  Cryptantha intermedia var. grandiflora (Rydb.) Cronquist -- not accepted
  Cryptantha jamesii var. pustulosa (Rydb.) H.D. Harr. -- not accepted
  Cryptantha minima Rydb. -- accepted -- little catseye, little cryptantha, small cryptantha
  Cryptantha pustulosa (Rydb.) Payson -- not accepted
  Cullen americana (L.) Rydb. -- not accepted -- American scurfpea
  Cullen americanum (L.) Rydb. -- accepted -- American scurfpea
  Cuscuta curta (Engelm.) Rydb. -- not accepted
  Cuscuta megalocarpa Rydb. -- not accepted -- big-fruit dodder, bigfruit dodder
  Cyanococcus canadensis (Kalm ex A. Rich.) Rydb. -- not accepted
  Cyanococcus corymbosus (L.) Rydb. -- not accepted
  Cyanococcus vacillans (Kalm ex Torr.) Rydb. -- not accepted
  Cymopterus longilobus (Rydb.) W.A. Weber -- not accepted
  Dalea adenopoda (Rydb.) Isely -- not accepted -- Tampa prairie clover
  Dalea carthagenensis var. floridana (Rydb.) Barneby -- accepted -- Florida prairie-clover
  Dalea carthaginensis var. floridana (Rydb.) Barneby -- not accepted
  Dalea exserta (Rydb.) Gentry -- accepted -- Mexican prairie clover, Mexican prairie-clover
  Dalea longipila (Rydb.) Cory -- not accepted
  Dalea mollis var. mollissima (Rydb.) Munz -- not accepted
  Dalea mollissima (Rydb.) Munz -- accepted -- hairy dalea, soft prairie clover
  Dalea nana var. carnescens (Rydb.) Kearney & Peebles -- accepted -- dwarf prairie clover, dwarf prairieclover
  Dalea neomexicana ssp. mollissima (Rydb.) Wiggins -- not accepted
  Dalea neomexicana var. longipila (Rydb.) Barneby -- accepted -- downy prairie clover, downy prairieclover
  Dalea pinnata var. adenopoda (Rydb.) Barneby -- accepted -- Tampa prairie clover
  Dalea versicolor var. glabrescens (Rydb.) Barneby -- accepted
  Dalea wislizeni var. sanctae-crucis (Rydb.) Kearney & Peebles -- not accepted
  Dasiphora fruticosa auct. non (L.) Rydb. -- not accepted
  Dasiphora fruticosa (L.) Rydb. -- accepted -- shrubby cinquefoil
  Dasiphora fruticosa ssp. tenuifolia (Willd. ex Schltdl.) Rydb. -- not accepted
  Dasyochloa Willd. ex Rydb. -- accepted -- woollygrass
  Dasyochloa pulchella (Kunth) Willd. ex Rydb. -- accepted -- fluffgrass, low woollygrass
  Dasystephana affinis (Griseb.) Rydb. -- not accepted
  Dasystephana glauca (Pall.) Rydb. -- not accepted
  Dasystephana interrupta (Greene) Rydb. -- not accepted
  Daubentonia drummondii Rydb. -- not accepted
  Delphinium albescens Rydb. -- not accepted
  Delphinium alpestre Rydb. -- accepted -- Colorado larkspur
  Delphinium brownii Rydb. -- not accepted
  Delphinium diversicolor Rydb. -- not accepted
  Delphinium geraniifolium Rydb. -- accepted -- Clark Valley larkspur
  Delphinium geyeri var. wootonii (Rydb.) K.C. Davis -- not accepted
  Delphinium glaucescens Rydb. -- accepted -- glaucus larkspur, smooth larkspur
  Delphinium glaucesens Rydb. -- not accepted
  Delphinium ramosum Rydb. -- accepted -- mountain larkspur
  Delphinium ramosum var. alpestre (Rydb.) W.A. Weber -- not accepted
  Delphinium robustum Rydb. -- accepted -- Wahatoya Creek larkspur
  Delphinium virescens ssp. wootonii (Rydb.) Ewan -- not accepted
  Delphinium virescens var. macroceratilis (Rydb.) Cory -- not accepted
  Delphinium virescens var. wootonii (Rydb.) Shinners -- not accepted
  Delphinium wootonii Rydb. -- accepted -- Organ Mountain larkspur
  Delphinium X diversicolor Rydb. -- accepted
  Delphinium xylorrhizum Rydb. -- not accepted -- larkspur
  Dentaria rupicola (O.E. Schulz) Rydb. -- not accepted
  Deschampsia alpicola Rydb. -- not accepted
  Deschampsia caespitosa var. alpicola (Rydb.) Á. & D. Löve & Kapoor -- not accepted
  Deschampsia cespitosa var. alpicola (Rydb.) D. Löve & B.M. Kapoor -- not accepted
  Deschampsia cespitosa var. pungens (Rydb.) B. Boivin -- not accepted
  Deschampsia ciliata (Vasey ex Beal) Rydb. -- not accepted
  Deschampsia confinis (Vasey ex Beal) Rydb. -- not accepted
  Deschampsia pungens Rydb. -- not accepted
  Descurainia brachycarpa var. nelsonii (Rydb.) O.E. Schulz -- not accepted
  Descurainia incana ssp. viscosa (Rydb.) Kartesz & Gandhi -- not accepted -- mountain tansy mustard, mountain tansymustard
  Descurainia incana var. viscosa (Rydb.) Dorn -- not accepted
  Descurainia incisa var. viscosa (Rydb.) G.A. Mulligan -- not accepted
  Descurainia intermedia (Rydb.) Daniels -- not accepted
  Descurainia nelsonii (Rydb.) Al-Shehbaz & Goodson -- accepted -- Nelson's tansymustard
  Descurainia pinnata ssp. intermedia (Rydb.) Detling -- not accepted -- western tansymustard
  Descurainia pinnata ssp. nelsonii (Rydb.) Detling -- not accepted -- Nelson's tansymustard
  Descurainia pinnata var. intermedia (Rydb.) C.L. Hitchc. -- not accepted
  Descurainia pinnata var. nelsonii (Rydb.) M. Peck -- not accepted
  Descurainia richardsonii ssp. viscosa (Rydb.) Detling -- not accepted
  Descurainia richardsonii var. viscosa (Rydb.) M. Peck -- not accepted
  Diarrhena arundinacea (Zea ex Lag.) Rydb. -- not accepted
  Dicentra cucullaria var. occidentalis (Rydb.) M. Peck -- not accepted
  Dicentra occidentalis (Rydb.) Fedde -- not accepted
  Dicoria canescens ssp. hispidula (Rydb.) D.D. Keck -- not accepted -- desert twinbugs
  Dicoria canescens var. hispidula (Rydb.) Cronquist -- not accepted
  Dicoria oblongifolia Rydb. -- not accepted
  Diholcos bisulcatus (Hook.) Rydb. -- not accepted
  Diphysa thurberi (A. Gray) Rydb. ex Standl. -- accepted -- Thurber's diphysa
  Distichlis dentata Rydb. -- not accepted
  Distichlis stricta (Torr.) Rydb. -- not accepted
  Distichlis stricta var. dentata (Rydb.) C.L. Hitchc. -- not accepted
  Distichlis stricta var. stricta (Torr.) Rydb. -- not accepted
  Dodecatheon cylindrocarpum Rydb. -- not accepted
  Dodecatheon frenchii (Vasey) Rydb. -- not accepted -- French's shootingstar
  Draba argyraea Rydb. -- not accepted
  Draba argyrea Rydb. -- accepted -- silver draba
  Draba brachystylis Rydb. -- accepted -- shortstyle draba, Wasatch draba
  Draba breweri var. cana (Rydb.) Rollins -- not accepted -- cushion draba, hoary whitlowgrass, lanceleaf draba, lanceolate draba
  Draba cana Rydb. -- accepted -- cushion draba
  Draba crassa Rydb. -- accepted -- thickleaf draba
  Draba grayana (Rydb.) C.L. Hitchc. -- accepted -- Gray's draba
  Draba lonchocarpa Rydb. -- accepted -- lancepod draba
  Draba lonchocarpa var. lonchocarpa Rydb. -- not accepted -- lancepod draba
  Draba mccallae Rydb. -- not accepted
  Draba nivalis ssp. lonchocarpa (Rydb.) Hultén -- not accepted
  Draba parryi Rydb. -- not accepted
  Draba sobolifera Rydb. -- accepted -- stolon draba, stolon whitlowgrass
  Dracocephalum formosius (Lunell) Rydb. -- not accepted
  Drymocallis Fourr. ex Rydb. -- accepted
  Drymocallis agrimonioides (Pursh) Rydb. -- not accepted
  Drymocallis arguta (Pursh) Rydb. -- accepted -- tall cinquefoil
  Drymocallis arizonica Rydb. -- accepted -- Arizona cinquefoil
  Drymocallis ashlandica (Greene) Rydb. -- accepted -- Ashland cinquefoil
  Drymocallis convallaria (Rydb.) Rydb. -- accepted -- cream cinquefoil
  Drymocallis cuneifolia Rydb. -- accepted
  Drymocallis cuneifolia var. cuneifolia Rydb. -- accepted
  Drymocallis fissa (Nutt.) Rydb. -- accepted -- bigflower cinquefoil
  Drymocallis glabrata Rydb. -- accepted -- Idaho drymocallis
  Drymocallis glandulosa (Lindl.) Rydb. -- accepted -- sticky cinquefoil
  Drymocallis glandulosa var. glandulosa (Lindl.) Rydb. -- accepted -- sticky cinquefoil
  Drymocallis hansenii (Greene) Rydb. -- accepted -- Hansen's cinquefoil
  Drymocallis lactea (Greene) Rydb. -- accepted
  Drymocallis lactea var. lactea (Greene) Rydb. -- accepted -- Sierran drymocallis, wood beauty
  Drymocallis micropetala Rydb. -- accepted -- smallpetal cinquefoil
  Drymocallis pseudorupestris (Rydb.) Rydb. -- accepted -- sticky cinquefoil
  Drymocallis pseudorupestris var. pseudorupestris (Rydb.) Rydb. -- accepted -- sticky cinquefoil
  Drymocallis rhomboidea (Rydb.) Rydb. -- accepted -- globose drymocallis, Siskiyou drymocallis
  Dugaldia grandiflora Rydb. -- not accepted
  Dugaldia hoopesii (A. Gray) Rydb. -- not accepted
  Dysodiopsis (A. Gray) Rydb. -- accepted -- dogfennel
  Dysodiopsis tagetoides (Torr. & A. Gray) Rydb. -- accepted -- false dogfennel, marygold dogweed
  Dyssodia pentachaeta var. puberula (Rydb.) Strother -- not accepted
  Eatonia intermedia Rydb. -- not accepted
  Eatonia obtusata var. purpurascens Vasey ex Rydb. & Shear -- not accepted
  Eatonia obtusata var. robusta Vasey ex Rydb. -- not accepted
  Eatonia robusta (Vasey ex L.H. Dewey) Rydb. -- not accepted
  Echinocactus subglacus Rydb. -- not accepted
  Echinocactus subglaucus Rydb. -- not accepted
  Echinocactus xeranthemoides (J.M. Coult.) Engelm. ex Rydb. -- not accepted
  Echinocereus roemeri (Muehlenpf.) Rydb. -- not accepted
  Echinochloa crus-galli var. mutica (Elliott) Rydb. -- not accepted
  Echinochloa microstachya (Wiegand) Rydb. -- not accepted
  Echinochloa occidentalis (Wiegand) Rydb. -- not accepted
  Echinochloa pungens (Poir.) Rydb. -- not accepted
  Echinochloa pungens var. pungens (Poir.) Rydb. -- not accepted
  Elaeagnus commutata Bernh. ex Rydb. -- accepted -- silverberry
  Elatine californica var. williamsii (Rydb.) Fassett -- not accepted
  Elatine rubella Rydb. -- accepted -- southwestern waterwort
  Eleocharis flavescens var. thermalis (Rydb.) Cronquist -- not accepted -- yellow spikerush
  Eleocharis thermalis Rydb. -- not accepted
  Elephantella groenlandica (Retz.) Rydb. -- not accepted
  Elmera Rydb. -- accepted -- coralbells
  Elmera racemosa (S. Watson) Rydb. -- accepted -- yellow coralbells
  Elmera racemosa var. racemosa (S. Watson) Rydb. -- not accepted -- yellow coralbells
  Elodea linearis (Rydb.) H. St. John -- not accepted -- Nashville waterweed
  Elymus ambiguus var. strigosus (Rydb.) Hitchc. -- not accepted
  Elymus jejunus (Ramaley) Rydb. -- not accepted
  Elymus marginalis Rydb. -- not accepted
  Elymus petersonii Rydb. -- not accepted
  Elymus smithii (Rydb.) Gould -- not accepted
  Elymus strigosus Rydb. -- not accepted
  Elymus villiflorus Rydb. -- not accepted
  Elymus vulpinus Rydb. -- not accepted -- Rydberg's wildrye
  Elytrigia smithii (Rydb.) Á. Löve -- not accepted
  Elytrigia smithii (Rydb.) Nevski -- not accepted
  Epilobium paniculatum var. laevicaule (Rydb.) Munz -- not accepted
  Epilobium paniculatum var. tracyi (Rydb.) Munz -- not accepted
  Epilobium platyphyllum Rydb. -- not accepted
  Equisetum intermedium (A.A. Eaton) Rydb. -- not accepted
  Eremogone congesta var. cephaloidea (Rydb.) R.L. Hartm. & Rabeler -- accepted -- sharptip sandwort
  Eremogone congesta var. lithophila (Rydb.) Dorn -- accepted -- rock-loving sandwort
  Eremogone eastwoodiae (Rydb.) Ikonn. -- accepted -- Eastwood's sandwort
  Eremogone eastwoodiae var. eastwoodiae (Rydb.) Ikonn. -- accepted -- Eastwood's sandwort
  Ericameria cervina (S. Watson) Rydb. -- accepted -- deer goldenbush, deer heath-goldenrod, deer heathgoldenrod
  Ericameria discoidea var. linearis (Rydb.) G.L. Nesom -- not accepted -- whitestem goldenbush
  Ericameria filifolia (Rydb.) L.C. Anderson -- not accepted
  Ericameria linearis (Rydb.) R.P. Roberts & Urbatsch -- accepted -- whitestem goldenbush
  Ericameria nauseosa ssp. nauseosa var. salicifolia (Rydb.) G.L. Nesom & Baird -- not accepted
  Ericameria nauseosa var. salicifolia (Rydb.) G.L. Nesom & Baird -- accepted -- rubber rabbitbrush
  Ericameria obovata (Rydb.) G.L. Nesom -- accepted -- Rydberg's goldenbush
  Ericameria paniculata (A. Gray) Rydb. -- accepted -- desert rabbitbrush, Mojave rabbitbrush
  Erigeron arenarioides (D.C. Eaton ex A. Gray) A. Gray ex Rydb. -- accepted -- sand fleabane
  Erigeron compositus var. multifidus (Rydb.) J.F. Macbr. & Payson -- not accepted
  Erigeron conspicuus Rydb. -- not accepted
  Erigeron debilis (A. Gray) Rydb. -- not accepted
  Erigeron evermannii Rydb. -- accepted -- Evermann's fleabane
  Erigeron flabellifolius Rydb. -- accepted -- fanleaf fleabane
  Erigeron formosissimus var. viscidus (Rydb.) Cronquist -- not accepted -- beautiful fleabane
  Erigeron glabellus var. viscidus (Rydb.) B. Boivin -- not accepted
  Erigeron glabellus var. yukonensis (Rydb.) Hultén -- not accepted
  Erigeron gracilis Rydb. -- accepted -- quill fleabane
  Erigeron mancus Rydb. -- accepted -- depauperate fleabane
  Erigeron minor (Hook.) Rydb. -- not accepted
  Erigeron nematophyllus Rydb. -- accepted -- needleleaf fleabane
  Erigeron oblanceolatus Rydb. -- not accepted
  Erigeron ochroleucus var. scribneri (Canby ex Rydb.) Cronquist -- not accepted -- buff fleabane
  Erigeron pulcherrimus var. wyomingia (Rydb.) Cronquist -- not accepted
  Erigeron speciosus var. conspicuus (Rydb.) Breitung -- not accepted
  Erigeron subtrinervis Rydb. ex Porter & Britton -- accepted -- three-nerve fleabane, threenerve fleabane, threeveined fleabane
  Erigeron subtrinervis ssp. conspicuus (Rydb.) Cronquist -- not accepted
  Erigeron subtrinervis var. conspicuus (Rydb.) Cronquist -- not accepted -- threenerve fleabane
  Erigeron subtrinervis var. subtrinervis Rydb. ex Porter & Britton -- not accepted -- threenerve fleabane
  Erigeron superbus Greene ex Rydb. -- not accepted
  Erigeron vetensis Rydb. -- accepted -- early bluetop fleabane
  Erigeron viscidus Rydb. -- not accepted
  Erigeron wyomingia Rydb. -- not accepted
  Erigeron yukonensis Rydb. -- accepted -- Yukon fleabane
  Eriocoma caduca (Beal) Rydb. -- not accepted
  Eriocoma hymenoides (Roem. & Schult.) Rydb. -- not accepted
  Eriogonum brandegeei Rydb. -- accepted -- Brandegee's buckwheat, Brandegee's wild buckwheat
  Eriogonum chrysops Rydb. -- accepted -- bitterroot buckwheat, golden buckwheat
  Eriogonum clutei Rydb. -- not accepted
  Eriogonum flavum var. polyphyllum (Small ex Rydb.) M.E. Jones -- not accepted -- alpine golden buckwheat
  Eriogonum lagopus Rydb. -- not accepted -- parasol buckwheat
  Eriogonum mancum Rydb. -- accepted -- imperfect buckwheat
  Eriogonum microthecum var. idahoense (Rydb.) S. Stokes -- not accepted
  Eriogonum nebraskense Rydb. -- not accepted
  Eriogonum ochroleucum Small ex Rydb. -- not accepted
  Eriogonum ovalifolium ssp. chrysops (Rydb.) S. Stokes ex M. Peck -- not accepted
  Eriogonum ovalifolium ssp. ochroleucum (Small ex Rydb.) S. Stokes -- not accepted
  Eriogonum ovalifolium var. ochroleucum (Small ex Rydb.) M. Peck -- accepted -- cushion buckwheat
  Eriogonum pauciflorum var. nebraskense (Rydb.) Reveal -- not accepted -- Nebraska buckwheat
  Eriogonum polyphyllum Small ex Rydb. -- not accepted
  Eriogonum spathuiforme Rydb. -- not accepted
  Eriogonum spathulatum ssp. spathuiforme (Rydb.) S. Stokes -- not accepted
  Eriogonum X nebraskense Rydb. (pro. sp.) -- accepted -- Nebraska buckwheat
  Eriophyllum confertiflorum var. discoideum (Rydb.) Munz -- not accepted
  Eriophyllum confertiflorum var. tridactylum (Rydb.) Munz -- not accepted
  Eriophyllum lanatum var. monoense (Rydb.) Jeps. -- not accepted
  Eriophyllum latilobum Rydb. -- accepted -- San Mateo woolly sunflower
  Eriophyllum wallacei ssp. australe (Rydb.) Wiggins -- not accepted
  Eritrichium elongatum (Rydb.) Wight -- not accepted
  Eritrichium howardii (A. Gray) Rydb. -- accepted -- Howard's alpine forget-me-not
  Eritrichium nanum var. elongatum (Rydb.) Cronquist -- accepted -- arctic alpine forget-me-not
  Erocallis triphylla (S. Watson) Rydb. -- not accepted
  Erxlebenia minor (L.) Rydb. -- not accepted
  Erysimum amoenum (Greene) Rydb. -- not accepted
  Erysimum angustatum Rydb. -- not accepted -- Contra Costa wallflower, Dawson wallflower
  Erysimum argillosum (Greene) Rydb. -- not accepted
  Erysimum asperrimum (Greene) Rydb. -- not accepted
  Erysimum asperum var. angustatum (Rydb.) B. Boivin -- not accepted
  Erysimum nivale (Greene) Rydb. -- not accepted
  Eschenbachia coulteri (A. Gray) Rydb. -- not accepted
  Eupatorium holzingeri Rydb. -- not accepted
  Eupatorium purpureum var. holzingeri (Rydb.) E. Lamont -- not accepted -- Holzinger's eupatorium
  Eupatorium texense (Torr. & A. Gray) Rydb. -- not accepted
  Euphorbia albicaulis Rydb. -- not accepted
  Eurotia lanata var. subspinosa (Rydb.) Kearney & Peebles -- not accepted
  Euthamia glutinosa Rydb. -- not accepted
  Eutrochium purpureum var. holzingeri (Rydb.) E.E. Lamont -- accepted -- Holzinger's eupatorium
  Fagonia pachyacantha Rydb. -- accepted -- sticky fagonbush, sticky fagonia
  Festuca brachyphylla ssp. saximontana (Rydb.) Hultén -- not accepted
  Festuca calligera (Piper) Rydb. -- accepted -- southwest fescue
  Festuca campestris Rydb. -- accepted -- rough fescue
  Festuca earlei Rydb. -- accepted -- Earle's fescue
  Festuca ingrata (Hack. ex Beal) Rydb. -- not accepted
  Festuca ingrata var. ingrata (Hack. ex Beal) Rydb. -- not accepted
  Festuca ingrata var. nudata Vasey ex Rydb. -- not accepted
  Festuca minutiflora Rydb. -- accepted -- small-flower fescue, smallflower fescue
  Festuca ovina ssp. saximontana (Rydb.) St.-Yves -- not accepted
  Festuca ovina var. minutiflora (Rydb.) J.T. Howell -- not accepted
  Festuca ovina var. saximontana (Rydb.) Gleason -- not accepted
  Festuca rubra ssp. vallicola (Rydb.) Pavlick -- accepted -- red fescue
  Festuca saximontana Rydb. -- accepted -- mountain fescue, Rocky Mountain fescue
  Festuca saximontana ssp. saximontana Rydb. -- not accepted
  Festuca saximontana var. saximontana Rydb. -- accepted -- Rocky Mountain fescue
  Festuca vallicola Rydb. -- not accepted
  Filipendula denudata (J. Presl & C. Presl) Rydb. -- not accepted
  Flaveria latifolia (J.R. Johnst.) Rydb. -- not accepted
  Flaveria oppositifolia auct. non (DC.) Rydb. -- not accepted
  Flaveria X latifolia (J.R. Johnst.) Long & Rhamstine non Flaveria latifolia (J.R. Johnst.) Rydb. -- not accepted
  Floerkea occidentalis Rydb. -- not accepted
  Fragaria australis (Rydb.) Rydb. -- not accepted
  Fragaria californica var. franciscana Rydb. -- not accepted
  Fragaria crinita Rydb. -- not accepted -- Pacific strawberry
  Fragaria glauca (S. Watson) Rydb. -- not accepted
  Fragaria ovalis (Lehm.) Rydb. -- not accepted
  Fragaria pauciflora Rydb. -- not accepted
  Fragaria platypetala Rydb. -- not accepted
  Fragaria platypetala var. sibbaldifolia (Rydb.) Jeps. -- not accepted
  Fragaria sibbaldifolia Rydb. -- not accepted
  Fragaria suksdorfii Rydb. -- not accepted
  Fragaria truncata Rydb. -- not accepted
  Fragaria vesca var. alba (Ehrh.) Rydb. -- not accepted
  Fragaria vesca var. crinita (Rydb.) C.L. Hitchc. -- not accepted
  Fragaria virginiana ssp. platypetala (Rydb.) Staudt -- accepted -- Virginia strawberry
  Fragaria virginiana var. australis Rydb. -- not accepted
  Fragaria virginiana var. platypetala (Rydb.) H.M. Hall -- not accepted
  Fragaria virginiana var. terrae-novae (Rydb.) Fernald & Wiegand -- not accepted
  Franseria confertiflora (DC.) Rydb. -- not accepted
  Franseria linearis Rydb. -- not accepted
  Franseria strigulosa Rydb. -- not accepted
  Frasera angustifolia (Rydb.) Rydb. -- not accepted
  Frasera speciosa var. angustifolia Rydb. -- not accepted
  Frasera speciosa var. stenosepala Rydb. -- not accepted
  Frasera stenosepala (Rydb.) Rydb. -- not accepted
  Gaillardia arizonica var. pringlei (Rydb.) S.F. Blake -- not accepted -- Pringle's blanketflower
  Gaillardia flava Rydb. -- not accepted -- yellow blanketflower
  Gaillardia mearnsii Rydb. -- not accepted
  Gaillardia pinnatifida var. linearis (Rydb.) Biddulph -- not accepted -- red dome blanketflower, reddome blanketflower
  Gaillardia pringlei Rydb. -- not accepted
  Gaillardia rigida Small ex Rydb. -- not accepted
  Gaillardia villosa Rydb. -- not accepted
  Galactia mississippiensis (Vail) Rydb. -- not accepted
  Galarhoeus arkansanus (Engelm. & A. Gray) Small ex Rydb. -- not accepted
  Galarhoeus commutatus (Engelm. ex A. Gray) Small ex Rydb. -- not accepted
  Galarhoeus cyparissias (L.) Small ex Rydb. -- not accepted
  Galarhoeus esula (L.) Rydb. -- not accepted
  Galarhoeus lucidus (Waldst. & Kit.) Rydb. -- not accepted
  Galarhoeus missouriensis (Norton) Rydb. -- not accepted
  Galarhoeus obtusatus (Pursh) Small ex Rydb. -- not accepted
  Galarhoeus peplus (L.) Rydb. -- not accepted
  Galarhoeus robustus (Engelm.) Rydb. -- not accepted
  Galeorchis spectabilis (L.) Rydb. -- not accepted
  Galium asperulum (A. Gray) Rydb. -- not accepted
  Galium boreale var. linearifolium Rydb. -- not accepted
  Galium columbianum Rydb. -- not accepted
  Galium filipes Rydb. -- not accepted -- slenderstalk bedstraw
  Galium subbiflorum (Wiegand) Rydb. -- not accepted
  Galium trifidum ssp. columbianum (Rydb.) Hultén -- accepted -- threepetal bedstraw
  Gaultheria humifusa (Graham) Rydb. -- accepted -- alpine spicywintergreen, western wintergreen
  Gaura neomexicana ssp. coloradensis (Rydb.) P.H. Raven & D.P. Greg. -- not accepted -- Colorado beeblossom, Colorado butterfly plant
  Gaura neomexicana var. coloradensis (Rydb.) Munz -- not accepted -- Colorado butterfly plant
  Gayophytum helleri Rydb. -- not accepted
  Gayophytum intermedium Rydb. -- not accepted
  Gayophytum nuttallii var. intermedium (Rydb.) Munz -- not accepted
  Gentiana calycosa var. obtusiloba (Rydb.) C.L. Hitchc. -- not accepted
  Gentiana strictiflora (Rydb.) A. Nelson -- not accepted
  Gentianella strictiflora (Rydb.) W.A. Weber -- not accepted
  Geoprumnon crassicarpum (Nutt.) Rydb. -- not accepted
  Geoprumnon mexicanum (A. DC.) Rydb. -- not accepted
  Geoprumnon plattense (Nutt.) Rydb. -- not accepted
  Geoprumnon succulentum (Richardson) Rydb. -- not accepted
  Geoprumnon tennesseense (A. Gray ex Chapm.) Rydb. -- not accepted
  Geranium atropurpureum var. cowenii (Rydb.) Dorn -- not accepted -- western purple cranesbill
  Geranium canum Rydb. -- not accepted
  Geranium cowenii Rydb. -- not accepted
  Geranium fremontii var. cowenii (Rydb.) H.D. Harr. -- not accepted
  Geranium marginale Rydb. ex Hanks & Small -- not accepted -- western geranium
  Geranium nervosum Rydb. -- not accepted
  Geranium strigosum Rydb. -- not accepted
  Geranium viscosissimum ssp. nervosum (Rydb.) W.A. Weber -- not accepted
  Geranium viscosissimum var. nervosum (Rydb.) C.L. Hitchc. -- not accepted -- sticky purple geranium
  Geum camporum Rydb. -- not accepted
  Geum canadense var. camporum (Rydb.) Fernald & Weath. -- not accepted -- white avens
  Geum decurrens Rydb. -- not accepted
  Geum macrophyllum ssp. perincisum (Rydb.) Hultén -- not accepted
  Geum macrophyllum var. perincisum (Rydb.) Raup -- accepted -- large-leaf avens, largeleaf avens
  Geum oregonense (Scheutz) Rydb. -- not accepted
  Geum perincisum Rydb. -- not accepted
  Geum rossii var. turbinatum (Rydb.) C.L. Hitchc. -- not accepted -- Ross' avens
  Geum strictum var. decurrens (Rydb.) Kearney & Peebles -- not accepted
  Geum turbinatum Rydb. -- not accepted
  Gilia aggregata var. candida (Rydb.) Cronquist -- not accepted
  Gilia arizonica (Greene) Rydb. -- not accepted
  Gilia candida Rydb. -- not accepted
  Gilia cephaloidea Rydb. -- not accepted
  Gilia congesta var. frutescens (Rydb.) Cronquist -- not accepted
  Gilia frutescens Rydb. -- not accepted
  Gilia hutchinsifolia Rydb. -- not accepted -- desert pale gilia, desert pale gily-flower, Hutchin's gilia
  Gilia inconspicua var. tweedyi (Rydb.) Cronquist -- not accepted
  Gilia parvula Rydb. -- not accepted
  Gilia polyantha Rydb. -- not accepted
  Gilia roseata Rydb. -- not accepted
  Gilia sinuata var. tweedyi (Rydb.) Cronquist -- not accepted
  Gilia spicata var. cephaloidea (Rydb.) Constance & Rollins -- not accepted
  Gilia spicata var. tridactyla (Rydb.) Constance & Rollins -- not accepted
  Gilia subacaulis Rydb. -- not accepted -- pinyon gilia
  Gilia tenuituba Rydb. -- not accepted
  Gilia tridactyla Rydb. -- not accepted
  Gilia tweedyi Rydb. -- accepted -- Tweedy's gilia
  Giliastrum (Brand) Rydb. -- accepted
  Giliastrum acerosum (A. Gray) Rydb. -- accepted -- bluebowls
  Giliastrum rigidulum (Benth.) Rydb. -- accepted -- bluebowls
  Glandularia pumila (Rydb.) Umber -- accepted -- pink mock vervain, pink verbena
  Glyceria rigida (Nash) Rydb. -- not accepted
  Goodyera ophioides (Fernald) Rydb. -- not accepted
  Graphephorum brandegeei (Scribn.) Rydb. -- not accepted
  Graphephorum shearii (Scribn.) Rydb. -- not accepted
  Greeneocharis circumscissa (Hook. & Arn.) Rydb. -- not accepted
  Grindelia aphanactis Rydb. -- not accepted
  Grindelia columbiana (Piper) Rydb. -- not accepted -- Columbia River gumweed
  Grindelia laciniata Rydb. -- not accepted -- cut-leaf gumweed, cutleaf gumweed
  Grindelia nana var. integerrima (Rydb.) Steyerm. -- not accepted -- Idaho gumweed
  Grindelia nuda var. aphanactis (Rydb.) G.L. Nesom -- not accepted -- curlytop gumweed, rayless gumweed
  Grindelia serrulata Rydb. -- not accepted
  Grindelia squarrosa var. serrulata (Rydb.) Steyerm. -- not accepted -- curly-cup gumweed, curlycup gumweed, curlytop gumweed, gumweed, rosinweed, tarweed
  Grossularia inermis (Rydb.) Coville & Britton -- not accepted
  Guaiacum guatemalense Planch. ex Rydb. -- not accepted
  Gutierrezia linearis Rydb. -- not accepted
  Gymnadeniopsis Rydb. -- accepted
  Gymnadeniopsis clavellata (Michx.) Rydb. -- accepted -- small green wood orchid
  Gymnadeniopsis integra (Nutt.) Rydb. -- accepted -- yellow fringeless orchid
  Gymnadeniopsis nivea (Nutt.) Rydb. -- accepted -- snowy orchid
  Habenaria behringiana (Rydb.) Ames -- not accepted
  Habenaria dilatata var. media (Rydb.) Hultén -- not accepted
  Habenaria media (Rydb.) Niles -- not accepted
  Habenaria sparsiflora var. laxiflora (Rydb.) Correll -- not accepted
  Habenaria stricta (Lindl.) Rydb. -- not accepted
  Hackelia besseyi (Rydb.) J.L. Gentry -- accepted -- Bessey's stickseed
  Hackelia diffusa var. caerulescens (Rydb.) I.M. Johnst. -- not accepted
  Hackelia leptophylla (Rydb.) I.M. Johnst. -- not accepted
  Hamosa leptocarpa (Torr. & A. Gray) Rydb. -- not accepted
  Haplopappus annuus (Rydb.) Cory -- not accepted
  Haplopappus carthamoides ssp. rigidus (Rydb.) H.M. Hall -- not accepted
  Haplopappus carthamoides var. erythropappus (Rydb.) H. St. John -- not accepted
  Haplopappus carthamoides var. rigidus (Rydb.) M. Peck -- not accepted
  Haplopappus clementis (Rydb.) S.F. Blake -- not accepted
  Haplopappus lanuginosus ssp. andersonii (Rydb.) H.M. Hall -- not accepted
  Haplopappus lanuginosus var. andersonii (Rydb.) Cronquist -- not accepted
  Haplopappus macronema var. linearis (Rydb.) Dorn -- not accepted
  Haplopappus phyllocephalus ssp. annuus (Rydb.) H.M. Hall -- not accepted
  Haplopappus phyllocephalus var. annuus (Rydb.) Waterf. -- not accepted
  Haplopappus spinulosus ssp. glaberrimus (Rydb.) H.M. Hall -- not accepted
  Haplopappus spinulosus var. glaberrimus (Rydb.) S.F. Blake -- not accepted
  Haplopappus spinulosus var. turbinellus (Rydb.) S.F. Blake -- not accepted
  Haplopappus validus (Rydb.) Cory -- not accepted
  Hedeoma campora Rydb. -- not accepted
  Hedeoma longiflora Rydb. -- not accepted
  Hedysarum boreale var. cinerascens (Rydb.) Rollins -- not accepted
  Hedysarum boreale var. utahense (Rydb.) Rollins -- not accepted
  Hedysarum cinerascens Rydb. -- not accepted
  Hedysarum sulphurescens Rydb. -- accepted -- white sweetvetch
  Hedysarum utahense Rydb. -- not accepted
  Helenium linifolium Rydb. -- accepted -- slimleaf sneezeweed
  Helenium macranthum Rydb. -- not accepted
  Helenium pinnatifidum (Nutt.) Rydb. -- accepted -- southeastern sneezeweed
  Helenium rivulare (Greene) Rydb. -- not accepted
  Helianthus aridus Rydb. -- not accepted
  Helianthus laetiflorus var. subrhomboideus (Rydb.) Fernald -- not accepted
  Helianthus pauciflorus ssp. subrhomboideus (Rydb.) O. Spring & E.E. Schill. -- accepted -- stiff sunflower
  Helianthus pauciflorus var. subrhomboideus (Rydb.) Cronquist -- not accepted
  Helianthus rigidus ssp. laetiflorus (Rydb.) Heiser -- not accepted
  Helianthus rigidus ssp. subrhomboideus (Rydb.) Heiser -- not accepted
  Helianthus rigidus var. subrhomboideus (Rydb.) Cronquist -- not accepted
  Helianthus subrhomboideus Rydb. -- not accepted
  Heliotropium spathulatum Rydb. -- not accepted
  Hesperidanthus (B.L. Rob.) Rydb. -- accepted
  Hesperidanthus linearifolius (A. Gray) Rydb. -- accepted -- slimleaf plainsmustard
  Hesperochloa (Piper) Rydb. -- not accepted
  Hesperochloa kingii (S. Watson) Rydb. -- not accepted
  Hesperochloa kingii var. kingii (S. Watson) Rydb. -- not accepted
  Hesperopeuce mertensiana (Bong.) Rydb. -- not accepted
  Heterotheca barbata (Rydb.) Semple -- accepted -- Spokane false goldenaster
  Heterotheca depressa (Rydb.) Dorn -- not accepted
  Heterotheca fulcrata var. amplifolia (Rydb.) Semple -- accepted -- rockyscree false goldenaster
  Heterotheca horrida (Rydb.) V.L. Harms -- not accepted
  Heterotheca stenophylla var. angustifolia (Rydb.) Semple -- accepted -- stiffleaf false goldenaster
  Heterotheca villosa var. angustifolia (Rydb.) Semple -- not accepted
  Heterotheca villosa var. ballardii (Rydb.) Semple -- accepted -- hairy false goldenaster
  Heterotheca villosa var. depressa (Rydb.) Semple -- accepted -- hairy false goldenaster
  Heuchera abramsii Rydb. -- accepted -- San Gabriel alumroot
  Heuchera aceroides Rydb. -- not accepted
  Heuchera alba Rydb. -- accepted -- white alumroot
  Heuchera arkansana Rydb. -- not accepted
  Heuchera crinita Rydb. -- not accepted
  Heuchera curtisii var. crenata Rydb. -- not accepted
  Heuchera cylindrica var. suksdorfii (Rydb.) Dorn -- not accepted
  Heuchera diversifolia Rydb. -- not accepted
  Heuchera flabellifolia Rydb. -- not accepted -- Bridger Mountain alumroot, montane alumroot
  Heuchera flabellifolia var. flabellifolia Rydb. -- not accepted -- Bridger Mountain alumroot
  Heuchera grossulariifolia Rydb. -- accepted -- gooseberryleaf alumroot
  Heuchera grossulariifolia var. grossulariifolia Rydb. -- not accepted -- gooseberryleaf alumroot
  Heuchera hirsuticaulis (Wheelock) Rydb. -- not accepted
  Heuchera lancipetala Rydb. -- not accepted
  Heuchera longiflora Rydb. -- accepted -- goldeneye, longflower alumroot
  Heuchera longiflora var. aceroides (Rydb.) Rosend., Butters & Lakela -- not accepted
  Heuchera micrantha var. diversifolia (Rydb.) Rosend., Butters & Lakela -- accepted -- crevice alumroot
  Heuchera parishii Rydb. -- accepted -- Mill Creek alumroot
  Heuchera parvifolia var. flavescens (Rydb.) Rosend., Butters & Lakela -- not accepted -- littleleaf alumroot
  Heuchera parvifolia var. utahensis (Rydb.) Garrett -- not accepted -- Utah alumroot
  Heuchera pilosissima var. hemisphaerica (Rydb.) Rosend. -- not accepted -- seaside alumroot
  Heuchera pringlei Rydb. -- not accepted
  Heuchera sanguinea var. pulchra (Rydb.) Rosend. -- not accepted -- coralbells
  Heuchera scabra Rydb. -- not accepted
  Heuchera suksdorfii Rydb. -- not accepted
  Heuchera tenuifolia (Wheelock) Rydb. -- not accepted
  Heuchera villosa var. arkansana (Rydb.) E.B. Sm. -- accepted -- Arkansas alumroot
  Heuchera wootonii Rydb. -- accepted -- White Mountain alumroot
  Hieracium columbianum Rydb. -- not accepted
  Hieracium columbianum auct. non Rydb. -- not accepted
  Hieracium scabriusculum var. columbianum auct. non (Rydb.) Lepage -- not accepted
  Hieracium scabriusculum var. columbianum (Rydb.) Lepage -- not accepted
  Hieracium scouleri var. griseum (Rydb.) A. Nelson -- not accepted
  Hoita Rydb. -- accepted -- leather-root
  Hoita hallii Rydb. -- not accepted
  Hoita longiloba Rydb. -- not accepted
  Hoita macrostachya (DC.) Rydb. -- accepted -- large leather-root
  Hoita orbicularis (Lindl.) Rydb. -- accepted -- roundleaf leather-root
  Hoita rhombifolia (Torr.) Rydb. -- not accepted
  Hoita rhomboidea Rydb. -- not accepted
  Hoita strobilina (Hook. & Arn.) Rydb. -- accepted -- Loma prieta
  Holcophacos distortus (Torr. & A. Gray) Rydb. -- not accepted
  Holodiscus discolor ssp. franciscanus (Rydb.) Roy L. Taylor & MacBryde -- not accepted
  Holodiscus discolor ssp. microphyllus (Rydb.) A.E. Murray -- not accepted
  Holodiscus discolor var. franciscanus (Rydb.) Jeps. -- not accepted
  Holodiscus discolor var. microphyllus (Rydb.) Jeps. -- not accepted
  Holodiscus microphyllus Rydb. -- accepted
  Holodiscus microphyllus var. microphyllus Rydb. -- accepted -- rock spiraea
  Homalobus vexilliflexus (Sheldon) Rydb. -- not accepted
  Horckelia scandularis Rydb. -- not accepted
  Hordeum depressum (Scribn. & J.G. Sm.) Rydb. -- accepted -- dwarf barley
  Horkelia argyrocoma Rydb. -- not accepted
  Horkelia baileyi (S. Watson) Rydb. -- not accepted
  Horkelia bernardiana Rydb. -- not accepted
  Horkelia brownii Rydb. -- not accepted
  Horkelia caruifolia Rydb. ex Howell -- not accepted
  Horkelia clevelandii (Greene) Rydb. -- accepted -- Cleveland's horkelia
  Horkelia clevelandii var. clevelandii (Greene) Rydb. -- accepted -- Cleveland's horkelia
  Horkelia congdonis Rydb. -- not accepted
  Horkelia cuneata ssp. puberula (Rydb.) D.D. Keck -- not accepted -- wedgeleaf horkelia
  Horkelia cuneata var. puberula (Rydb.) Ertter & Reveal -- accepted -- wedgeleaf horkelia
  Horkelia daucifolia (Greene) Rydb. -- accepted -- carrotleaf horkelia
  Horkelia daucifolia ssp. daucifolia (Greene) Rydb. -- not accepted -- carrotleaf horkelia
  Horkelia daucifolia var. caruifolia (Rydb. ex Howell) Ertter & Reveal -- accepted -- carrotleaf horkelia
  Horkelia daucifolia var. daucifolia (Greene) Rydb. -- accepted -- carrotleaf horkelia
  Horkelia elata (Greene) Rydb. -- not accepted
  Horkelia flavescens Rydb. -- not accepted
  Horkelia frondosa (Greene) Rydb. -- not accepted
  Horkelia fusca ssp. pseudocapitata (Rydb. ex Howell) D.D. Keck -- not accepted -- littlehead horkelia
  Horkelia fusca var. brownii (Rydb.) Ertter & Reveal -- accepted -- bighead horkelia
  Horkelia fusca var. pseudocapitata (Rydb. ex Howell) M. Peck -- accepted
  Horkelia gordonii var. alpicola (Rydb. ex Howell) Rydb. -- not accepted
  Horkelia gordonii var. megalopetala Rydb. -- not accepted
  Horkelia hispidula Rydb. -- accepted -- White Mountain horkelia
  Horkelia howellii (Greene) Rydb. -- accepted
  Horkelia pseudocapitata Rydb. ex Howell -- not accepted
  Horkelia puberula Rydb. -- not accepted
  Horkelia purpurascens ssp. congdonis (Rydb.) Abrams -- not accepted
  Horkelia sericea (A. Gray) Rydb. -- not accepted
  Horkelia sericoleuca Rydb. -- not accepted
  Horkelia tridentata ssp. flavescens (Rydb.) D.D. Keck -- not accepted -- threetooth honeydew, threetooth horkelia
  Horkelia tridentata var. flavescens (Rydb.) Ertter & Reveal -- accepted -- threetooth horkelia
  Horkelia truncata Rydb. -- accepted -- Ramona horkelia
  Horkeliella (Rydb.) Rydb. -- accepted -- false horkelia
  Horkeliella congdonis (Rydb.) Rydb. -- accepted -- Congdon's false horkelia
  Horkeliella purpurascens (S. Watson) Rydb. -- accepted -- purple false horkelia
  Hulsea callicarpha (H.M. Hall) S. Watson ex Rydb. -- not accepted
  Hulsea carnosa Rydb. -- not accepted
  Hulsea larsenii (A. Gray) Rydb. -- not accepted
  Hulsea mexicana Rydb. -- accepted -- Mexican alpinegold
  Hymenoclea pentalepis Rydb. -- not accepted
  Hymenoclea salsola var. pentalepis (Rydb.) L.D. Benson -- not accepted -- burrobrush, white burrobrush
  Hymenopappus cinereus Rydb. -- not accepted
  Hymenopappus filifolius var. cinereus (Rydb.) I.M. Johnst. -- accepted -- fine-leaf woollywhite, fineleaf hymenopappus
  Hymenopappus filifolius var. nanus (Rydb.) B.L. Turner -- accepted -- fineleaf hymenopappus
  Hymenopappus filifolius var. tomentosus (Rydb.) B.L. Turner -- accepted -- finehair hymenopappus
  Hymenoxys helenioides (Rydb.) Cockerell -- accepted -- Intermountain bitterweed, Intermountain hymenoxys, Intermountain rubberweed
  Hymenoxys quinquesquamata Rydb. -- accepted -- rincon rubberweed
  Hypericum mitchellianum Rydb. -- not accepted -- Blue Ridge St. Johnswort
  Hypericum X mitchellianum Rydb. (pro sp.) -- accepted -- Blue Ridge St. Johnswort
  Hypopitys latisquama Rydb. -- not accepted
  Ibidium strictum (Rydb.) House -- not accepted
  Iliamna crandallii (Rydb.) Wiggins -- accepted -- Crandall's wild hollyhock
  Iliamna grandiflora (Rydb.) Wiggins -- accepted -- large-flower wild hollyhock, largeflower wild hollyhock, wild hollyhock
  Impatiens aurella Rydb. -- accepted -- paleyellow touch-me-not
  Impatiens nortonii Rydb. -- not accepted
  Impatiens occidentalis Rydb. -- not accepted
  Ipomopsis aggregata ssp. candida (Rydb.) V.E. Grant & A.D. Grant -- accepted -- scarlet gilia, scarlet skyrocket
  Ipomopsis aggregata var. tenuilobus (Rydb.) Dorn -- not accepted
  Ipomopsis aggregata var. tenuituba (Rydb.) Dorn -- not accepted
  Ipomopsis candida (Rydb.) W.A. Weber -- not accepted
  Ipomopsis congesta ssp. frutescens (Rydb.) A.G. Day -- accepted -- ballhead gilia, ballhead ipomopsis
  Ipomopsis frutescens (Rydb.) V.E. Grant -- not accepted
  Ipomopsis polyantha (Rydb.) V.E. Grant -- accepted -- Pagosa ipomopsis, Pagosa skyrocket
  Ipomopsis roseata (Rydb.) V.E. Grant -- accepted -- rosy ipomopsis
  Ipomopsis spicata ssp. orchidacea var. cephaloidea (Rydb.) Wilken & R.L. Hartm. -- not accepted -- orchid ipomopsis
  Ipomopsis spicata ssp. tridactyla (Rydb.) Wilken & R.L. Hartm. -- accepted -- spiked ipomopsis
  Ipomopsis spicata var. cephaloidea (Rydb.) Wilken & R.L. Hartm. -- accepted -- orchid ipomopsis
  Ipomopsis tenuituba (Rydb.) V.E. Grant -- accepted -- slender-tube skyrocket, slendertube skyrocket
  Ipomopsis tenuituba ssp. tenuituba (Rydb.) V.E. Grant -- accepted -- slendertube skyrocket
  Ipomopsis tridactyla (Rydb.) S.L. Welsh -- not accepted -- Cedar Breaks gilia
  Isocoma wrightii (A. Gray) Rydb. -- not accepted
  Isopappus validus Rydb. -- not accepted
  Iva ambrosiifolia ssp. lobata (Rydb.) R. C. Jacks. -- not accepted
  Iva ambrosiifolia var. lobata (Rydb.) B.L. Turner -- not accepted
  Iva ambrosiifolia var. lobata (Rydb.) R. C. Jacks. -- not accepted
  Ivesia argyrocoma (Rydb.) Rydb. -- accepted -- silver-haired ivesia, silverhair mousetail
  Ivesia argyrocoma var. argyrocoma (Rydb.) Rydb. -- accepted -- silverhair mousetail
  Ivesia callida (H.M. Hall) Rydb. -- accepted -- Tahquitz ivesia, Tahquitz mousetail
  Ivesia campestris (M.E. Jones) Rydb. -- accepted -- field mousetail
  Ivesia eremica (Coville) Rydb. -- not accepted
  Ivesia gordonii var. alpicola (Rydb. ex Howell) Ertter & Reveal -- accepted -- Gordon's ivesia
  Ivesia lycopodioides ssp. megalopetala (Rydb.) D.D. Keck -- not accepted -- clubmoss mousetail
  Ivesia lycopodioides ssp. scandularis (Rydb.) D.D. Keck -- not accepted -- clubmoss mousetail
  Ivesia lycopodioides var. megalopetala (Rydb.) Ertter & Reveal -- accepted -- clubmoss mousetail
  Ivesia lycopodioides var. scandularis (Rydb.) Ertter & Reveal -- accepted -- clubmoss mousetail
  Ivesia purpurascens ssp. congdonis (Rydb.) D.D. Keck -- not accepted
  Ivesia sericoleuca (Rydb.) Rydb. -- accepted -- Plumas ivesia, Plumas mousetail
  Ivesia setosa (S. Watson) Rydb. -- accepted
  Ivesia tweedyi Rydb. -- accepted -- Tweedy's ivesia
  Juncoides intermedium (Thuill.) Rydb. -- not accepted
  Juncus arcticus ssp. ater (Rydb.) Hultén -- not accepted
  Juncus ater Rydb. -- not accepted
  Juncus balticus ssp. ater (Rydb.) Snogerup -- accepted
  Juncus balticus var. vallicola Rydb. -- not accepted -- valley rush
  Juncus ensifolius var. brunnescens (Rydb.) Cronquist -- not accepted
  Juncus jonesii Rydb. -- not accepted
  Juncus tracyi Rydb. -- not accepted -- Tracy rush, Tracy's rush
  Juncus tweedyi Rydb. -- not accepted -- Tweedy rush, Tweedy's rush
  Kallstroemia caribaea Rydb. -- not accepted
  Kallstroemia intermedia Rydb. -- not accepted
  Kelseya Rydb. -- accepted
  Kelseya uniflora (S. Watson) Rydb. -- accepted -- oneflower kelseya
  Kelseyi (S. Watson) Rydb. -- not accepted
  Kelseyi uniflora (S. Watson) Rydb. -- not accepted
  Kneiffia latifolia Rydb. -- not accepted
  Kochia vestita (S. Watson) Rydb. -- not accepted
  Koeleria latifrons (Domin) Rydb. -- not accepted
  Kuhnistera adenopoda Rydb. -- not accepted
  Laphamia rotundata Rydb. -- not accepted
  Lappula americana (A. Gray) Rydb. -- not accepted
  Lappula redowskii var. occidentalis (S. Watson) Rydb. -- not accepted
  Lathyrus brachycalyx Rydb. -- accepted -- Bonneville pea, Bonneville peavine, Bonneville vetchling, Rydberg's peavine
  Lathyrus brachycalyx ssp. brachycalyx Rydb. -- not accepted -- Bonneville pea, Bonneville peavine
  Lathyrus brachycalyx var. brachycalyx Rydb. -- accepted -- Bonneville pea
  Lathyrus incanus (J.G. Sm. & Rydb.) Rydb. -- not accepted
  Lathyrus laetivirens Greene ex Rydb. -- accepted -- aspen pea, aspen peavine, aspen vetchling, plateau peavine
  Lathyrus lanszwertii var. laetivirens (Greene ex Rydb.) S.L. Welsh -- not accepted
  Lathyrus lanszwertii var. leucanthus (Rydb.) Dorn -- accepted -- Arizona peavine, aspen peavine, Nevada pea
  Lathyrus leucanthus Rydb. -- not accepted
  Lathyrus leucanthus var. laetivirens (Greene ex Rydb.) C.L. Hitchc. -- not accepted
  Lathyrus polymorphus ssp. incanus (J.G. Sm. & Rydb.) C.L. Hitchc. -- not accepted -- hoary pea, hoary vetchling
  Lathyrus polymorphus var. incanus (J.G. Sm. & Rydb.) Dorn -- accepted -- hoary pea
  Lathyrus schaffneri Rydb. -- not accepted
  Lathyrus stipulaceus var. incanus (J.G. Sm. & Rydb.) Butters & H. St. John -- not accepted
  Lepidium crenatum (Greene) Rydb. -- accepted -- alkali pepperweed
  Lepidium densiflorum var. elongatum (Rydb.) Thell. -- not accepted -- tall pepperweed
  Lepidium elongatum Rydb. -- not accepted
  Lepidium jonesii Rydb. -- not accepted
  Lepidium lasiocarpum var. georginum (Rydb.) C.L. Hitchc. -- not accepted
  Lepidium montanum var. jonesii (Rydb.) C.L. Hitchc. -- not accepted -- Jones pepperweed, Jones' pepperweed
  Leptodactylon nuttallii (A. Gray) Rydb. -- not accepted
  Leptodactylon pungens ssp. brevifolium (Rydb.) Wherry -- not accepted
  Leptodactylon watonii (A. Gray) Rydb. -- not accepted
  Leptodactylon watsonii (A. Gray) Rydb. -- not accepted -- Watson's prickly gilia, Watson's prickly phlox
  Lesquerella alpina var. spathulata (Rydb.) Payson -- not accepted
  Lesquerella alpina var. spatulata (Rydb.) Payson -- not accepted -- alpine bladderpod
  Lesquerella arenosa (Richardson) Rydb. -- not accepted -- Great Plains bladderpod
  Lesquerella arenosa var. arenosa (Richardson) Rydb. -- not accepted -- Great Plains bladderpod
  Lesquerella engelmannii ssp. ovalifolia (Rydb. ex Britton) C. Clark -- not accepted
  Lesquerella ovalifolia Rydb. -- not accepted -- ovalleaf bladderpod, roundleaf bladderpod
  Lesquerella ovalifolia ssp. ovalifolia Rydb. -- not accepted -- roundleaf bladderpod
  Lesquerella spathulata Rydb. -- not accepted
  Lesquerella spatulata Rydb. -- not accepted
  Lesquerella utahensis Rydb. -- not accepted -- Utah bladderpod
  Leucanthemum leucanthemum (L.) Rydb. -- not accepted
  Leuciva Rydb. -- accepted
  Leuciva dealbata (A. Gray) Rydb. -- accepted -- woolly marsh elder
  Leucocoma alpina (L.) Rydb. -- not accepted
  Leucocraspedum albicaule (Douglas ex Griseb.) Rydb. -- not accepted
  Leucocraspedum albomarginatum (S. Watson) Rydb. -- not accepted
  Leucocraspedum montanum (Mulford) Rydb. -- not accepted
  Leucophysalis Rydb. -- accepted
  Leucophysalis grandiflora (Hook.) Rydb. -- accepted -- large false groundcherry
  Lewisia columbiana ssp. congdonii (Rydb.) Ferris -- not accepted
  Lewisia congdonii (Rydb.) S. Clay -- accepted -- Congdon's lewisia
  Lewisia disepala Rydb. -- accepted -- Yosemite bitterroot, Yosemite lewisia
  Lewisia glandulosa (Rydb.) Dempster -- not accepted -- Sierra lewisia
  Lewisia minor Rydb. -- not accepted
  Lewisia pygmaea ssp. glandulosa (Rydb.) Ferris -- not accepted
  Lewisia rediviva ssp. minor (Rydb.) A.H. Holmgren -- not accepted
  Lewisia rediviva var. minor (Rydb.) Munz -- accepted -- bitter root, Oregon bitterroot
  Liatris bebbiana Rydb. -- not accepted
  Liatris compacta (Torr. & A. Gray) Rydb. -- accepted -- scaly blazing star
  Liatris glabrata Rydb. -- not accepted
  Liatris hirsuta Rydb. -- accepted -- scaly blazing star
  Liatris squarrosa var. glabrata (Rydb.) Gaiser -- accepted -- scaly blazing star, scaly gayfeather
  Liatris squarrosa var. hirsuta (Rydb.) Gaiser -- not accepted -- scaly blazing star, scaly gayfeather
  Liatris X fallacior (Lunell) Rydb. (pro sp.) -- accepted -- gayfeather
  Lidia obtusiloba (Rydb.) Á. Löve & D. Löve -- not accepted
  Ligusticum porteri var. brevilobum (Rydb.) Mathias & Constance -- accepted -- Porter's licorice-root, Porter's licoriceroot
  Limnalsine diffusa (Nutt.) Rydb. -- not accepted
  Limnanthes versicolor (Greene) Rydb. -- not accepted
  Limnia utahensis Rydb. -- not accepted
  Limnobotrya lacustris (Pers.) Rydb. -- not accepted
  Limnobotrya montigena (McClatchie) Rydb. -- not accepted
  Limnorchis dilatata (Pursh) Rydb. -- not accepted
  Limnorchis ensifolia Rydb. -- not accepted
  Limnorchis graminifolia Rydb. -- not accepted
  Limnorchis hyperborea (L.) Rydb. -- not accepted
  Limnorchis media Rydb. -- not accepted
  Limnorchis purpurascens Rydb. -- not accepted
  Limnorchis sparsiflora (S. Watson) Rydb. -- not accepted
  Limnorchis stricta (Lindl.) Rydb. -- not accepted
  Limnorchis thurberi (A. Gray) Rydb. -- not accepted
  Limnorchis viridiflora (Cham.) Rydb. -- not accepted
  Listera cordata ssp. nephrophylla (Rydb.) Á. Löve & D. Löve -- not accepted
  Listera cordata var. nephrophylla (Rydb.) Hultén -- not accepted -- heartleaf twayblade
  Listera nephrophylla Rydb. -- not accepted
  Lithophragma australe Rydb. -- not accepted
  Lithophragma brevilobum Rydb. -- not accepted
  Lithophragma bulbiferum Rydb. -- not accepted
  Lithophragma glabrum var. bulbiferum (Rydb.) Jeps. -- not accepted
  Lobelia kalmii var. strictiflora Rydb. -- not accepted
  Lobelia strictiflora (Rydb.) Lunell -- not accepted
  Lomatium latilobum (Rydb.) Mathias -- accepted -- Canyonlands biscuitroot, Slicrock desert-parsley
  Lomatium lineare (Rydb.) Mathias -- not accepted
  Lonicera dioica var. glaucescens (Rydb.) Butters -- not accepted -- limber honeysuckle
  Lonicera glaucescens (Rydb.) Rydb. -- not accepted
  Lotus longebracteatus Rydb. -- not accepted
  Lupinus adscendens Rydb. -- not accepted
  Lupinus arbustus ssp. pseudoparviflorus (Rydb.) D.B. Dunn -- accepted -- false lupine, longspur lupine
  Lupinus argenteus ssp. spathulatus (Rydb.) L.W. Hess & D.B. Dunn -- accepted -- silvery lupine
  Lupinus argenteus var. argentatus (Rydb.) Barneby -- not accepted
  Lupinus argenteus var. depressus (Rydb.) C.L. Hitchc. -- not accepted
  Lupinus argenteus var. macounii (Rydb.) R.J. Davis -- not accepted
  Lupinus argenteus var. stenophyllus (Rydb.) R.J. Davis -- not accepted
  Lupinus argentinus Rydb. -- not accepted
  Lupinus argentus var. spathulatus (Rydb.) L.W. Hess & D.B. Dunn -- not accepted
  Lupinus candicans Rydb. -- not accepted
  Lupinus comatus Rydb. -- not accepted
  Lupinus cyaneus Rydb. -- not accepted
  Lupinus depressus Rydb. -- accepted -- depressed lupine
  Lupinus evermannii Rydb. -- accepted -- Evermann's lupine
  Lupinus flavescens Rydb. -- not accepted
  Lupinus flavicaulis Rydb. -- not accepted
  Lupinus glabratus (S. Watson) Rydb. -- not accepted
  Lupinus jonesii Rydb. -- accepted -- Jones' lupine
  Lupinus latifolius ssp. leucanthus (Rydb.) Kenney & D.B. Dunn -- accepted -- broadleaf lupine
  Lupinus laxiflorus var. pseudoparviflorus (Rydb.) C.P. Sm. & H. St. John -- not accepted
  Lupinus laxispicatus Rydb. -- not accepted
  Lupinus laxus Rydb. -- not accepted
  Lupinus leucanthus Rydb. -- not accepted
  Lupinus lupinus Rydb. -- not accepted
  Lupinus macounii Rydb. -- not accepted
  Lupinus macrostachys Rydb. -- not accepted
  Lupinus maculatus Rydb. -- accepted -- spotted lupine
  Lupinus marianus Rydb. -- not accepted
  Lupinus monticola Rydb. -- accepted -- mountain lupine
  Lupinus odoratus var. rubens (Rydb.) Jeps. -- not accepted
  Lupinus pulcherrimus Rydb. -- not accepted
  Lupinus pusillus ssp. rubens (Rydb.) D.B. Dunn -- accepted -- rusty lupine
  Lupinus pusillus var. rubens (Rydb.) S.L. Welsh -- not accepted
  Lupinus roseolus Rydb. -- accepted -- rosy lupine
  Lupinus rubens Rydb. -- not accepted
  Lupinus scaposus Rydb. -- not accepted
  Lupinus scheuberae Rydb. -- not accepted
  Lupinus sericeus ssp. marianus (Rydb.) Fleak & D.B. Dunn -- accepted -- silky lupine
  Lupinus sericeus var. jonesii (Rydb.) S.L. Welsh -- not accepted
  Lupinus sericeus var. marianus (Rydb.) S.L. Welsh -- not accepted
  Lupinus spathulatus Rydb. -- not accepted
  Lupinus stenophyllus (Nutt.) Rydb. -- not accepted
  Lupinus subulatus Rydb. -- not accepted
  Luzula subcapitata (Rydb.) H.D. Harr. -- accepted -- Colorado woodrush
  Lychnis drummondii var. striata (Rydb.) Maguire -- not accepted
  Lycopus velutinus Rydb. -- not accepted
  Lysias hookeriana (Torr. ex A. Gray) Rydb. -- not accepted
  Lysias orbiculata (Pursh) Rydb. -- not accepted
  Lysiella obtusata (Banks ex Pursh) Rydb. -- not accepted
  Machaeranthera angustifolia Rydb. non Woot. & Standl. -- not accepted
  Machaeranthera annua (Rydb.) Shinners -- not accepted -- viscid tansyaster
  Machaeranthera coloradoensis var. brandegeei (Rydb.) T.J. Watson ex R.L. Hartm. -- not accepted -- Brandegee's tansyaster
  Machaeranthera fremontii Rydb. -- not accepted
  Machaeranthera glabella Greene ex Rydb. -- not accepted
  Machaeranthera leptophylla Rydb. -- not accepted
  Machaeranthera linearis Rydb. non Greene -- not accepted
  Machaeranthera phyllocephala var. annua (Rydb.) Shinners -- not accepted
  Machaeranthera pinnatifida ssp. pinnatifida var. glaberrima (Rydb.) B.L. Turner & R.L. Hartm. -- not accepted -- lacy tansyaster
  Machaeranthera pinnatifida var. glaberrima (Rydb.) B.L. Turner & R.L. Hartm. -- not accepted -- lacy tansyaster
  Machaeranthera rubricaulis Rydb. -- not accepted
  Machaeranthera selbyi Rydb. -- not accepted
  Macronema lineare Rydb. -- not accepted
  Macronema obovatum Rydb. non Haplopappus obovatus Phil. -- not accepted
  Margaranthus purpurascens Rydb. -- not accepted
  Meibomia pubens (Torr. & A. Gray) Rydb. -- not accepted
  Mentha glabrior (Hook.) Rydb. -- not accepted
  Mentha penardii (Briq.) Rydb. -- not accepted
  Mentzelia albicaulis var. ctenophora (Rydb.) H. St. John -- not accepted
  Mentzelia albicaulis var. gracilis (Rydb.) J. Darl. -- not accepted
  Mentzelia albicaulis var. tenerrima (Rydb.) H. St. John -- not accepted
  Mentzelia dispersa var. latifolia (Rydb.) J.F. Macbr. -- accepted -- bushy blazingstar
  Mentzelia gracilis (Rydb.) H.J. Thomps. & F.H. Lewis -- not accepted
  Mentzelia laciniata (Rydb.) J. Darl. -- accepted -- cutleaf blazingstar
  Mentzelia laevicaulis var. acuminata (Rydb.) A. Nelson & J.F. Macbr. -- not accepted
  Mentzelia sinuata (Rydb.) R.J. Hill -- accepted -- leechleaf blazingstar
  Meriolix intermedia Rydb. ex Small -- not accepted
  Meriolix melanoglottis Rydb. ex Small -- not accepted
  Meriolix oblanceolata Rydb. -- not accepted
  Mertensia arizonica var. leonardii (Rydb.) I.M. Johnst. -- not accepted
  Mertensia ciliata var. subpubescens (Rydb.) J.F. Macbr. & Payson -- not accepted
  Mertensia humilis Rydb. -- accepted -- Rocky Mountain bluebells
  Mertensia perplexa Rydb. -- not accepted
  Mertensia viridis var. cana (Rydb.) L.O. Williams -- not accepted
  Microphacos parviflorus (Pursh) Rydb. -- not accepted
  Miltitzia scopulina (A. Nelson) Rydb. -- not accepted
  Mimulus eastwoodiae Rydb. -- accepted -- crimson monkeyflower, Eastwood's monkey-flower, Eastwood's monkeyflower
  Mimulus gratioloides Rydb. -- not accepted
  Mimulus tolmiei (Benth.) Rydb. -- not accepted
  Minuartia macrantha (Rydb.) House -- accepted -- House's stitchwort
  Minuartia obtusiloba (Rydb.) House -- accepted -- alpine sandwort, twinflower sandwort
  Mirabilis lanceolata (Rydb.) Standl. -- not accepted
  Mitella oppositifolia Rydb. -- not accepted
  Mitella trifida var. violacea (Rydb.) Rosend. -- not accepted -- threeparted miterwort
  Mitella violacea Rydb. -- not accepted
  Mitella X intermedia Bruhin ex Small & Rydb. (pro. sp.) -- accepted -- intermediate miterwort
  Moldavica thymiflora (L.) Rydb. -- not accepted
  Monotropa hypopithys var. latisquama (Rydb.) Kearney & Peebles -- not accepted
  Monotropa hypopitys var. latisquama (Rydb.) Kearney & Peebles -- not accepted
  Monotropa latisquama (Rydb.) Hultén -- not accepted
  Montia funstonii Rydb. -- not accepted
  Montia perfoliata var. utahensis (Rydb.) Munz -- not accepted
  Montiastrum dichotomum (Nutt.) Rydb. -- not accepted
  Montiastrum lineare (Douglas ex Hook.) Rydb. -- not accepted
  Muhlenbergia aristulata Rydb. -- not accepted
  Muhlenbergia cuspidata (Torr. ex Hook.) Rydb. -- accepted -- plains muhly
  Muhlenbergia filiformis (Thurb. ex S. Watson) Rydb. -- accepted -- pullup muhly
  Muhlenbergia filiformis var. filiformis (Thurb. ex S. Watson) Rydb. -- accepted -- pullup muhly
  Muhlenbergia richardsonis (Trin.) Rydb. -- accepted -- mat muhly, muhlenbergie de Richardson, soft-leaf muhly
  Muhlenbergia simplex (Scribn.) Rydb. -- not accepted
  Muhlenbergia squarrosa (Trin.) Rydb. -- not accepted
  Muhlenbergia thurberi (Scribn.) Rydb. -- accepted -- Thurber muhly, Thurber's muhly
  Muhlenbergia wolfii (Vasey) Rydb. -- not accepted
  Musineon lineare (Rydb.) Mathias -- accepted -- narrowleaf wildparsley
  Musineon vaginatum Rydb. -- accepted -- sheathed wildparsley
  Myzorrhiza californica (Cham. & Schltdl.) Rydb. -- not accepted
  Myzorrhiza cooperi (A. Gray) Rydb. -- not accepted
  Myzorrhiza corymbosa Rydb. -- not accepted
  Myzorrhiza ludoviciana (Nutt.) Rydb. -- not accepted
  Myzorrhiza multiflora (Nutt.) Rydb. -- not accepted
  Myzorrhiza pinorum (Geyer ex Hook.) Rydb. -- not accepted
  Myzorrhiza tuberosa (A. Gray) Rydb. -- not accepted
  Negundo interius (Britton) Rydb. -- not accepted
  Nemexia lasioneura (Hook.) Rydb. -- not accepted
  Neomammillaria similis (Engelm.) Britton & Rose ex Rydb. -- not accepted
  Neottia nephrophylla (Rydb.) Szlach. -- not accepted
  Noccaea coloradensis (Rydb.) Holub -- not accepted
  Nuttallia humilis (A. Gray) Rydb. -- not accepted
  Nuttallia laciniata (Rydb.) Wooton & Standl. -- not accepted
  Nuttallia rusbyi (Wooton) Rydb. -- not accepted
  Nuttallia sinuata (Rydb.) Daniels -- not accepted
  Ochrocodon pudicus (Pursh) Rydb. -- not accepted
  Odontotrichum decompositum (A. Gray) Rydb. -- not accepted
  Odostemon aquifolium (Pursh) Rydb. -- not accepted
  Odostemon fremontii (Torr.) Rydb. -- not accepted
  Odostemon nervosus (Pursh) Rydb. -- not accepted
  Oenothera biennis var. strigosa (Rydb.) Piper -- not accepted
  Oenothera caespitosa ssp. crinita (Rydb.) Munz -- not accepted -- tufted evening primrose, tufted evening-primrose
  Oenothera caespitosa ssp. macroglottis (Rydb.) W.L. Wagner, Stockh. & W.M. Klein -- not accepted -- tufted evening primrose, tufted evening-primrose
  Oenothera caespitosa var. crinita (Rydb.) Munz -- not accepted
  Oenothera caespitosa var. macroglottis (Rydb.) Cronquist -- not accepted
  Oenothera cespitosa ssp. crinita (Rydb.) Munz -- accepted -- tufted evening primrose, tufted eveningprimrose
  Oenothera cespitosa ssp. macroglottis (Rydb.) W.L. Wagner, Stockh. & W.M. Klein -- accepted -- tufted evening primrose, tufted eveningprimrose
  Oenothera cespitosa var. crinita (Rydb.) Munz -- not accepted
  Oenothera cespitosa var. macroglottis (Rydb.) Cronquist -- not accepted
  Oenothera coloradensis (Rydb.) W.L. Wagner & Hoch -- accepted -- New Mexico beeblossom
  Oenothera coloradensis ssp. coloradensis (Rydb.) W.L. Wagner & Hoch -- accepted -- Colorado beeblossom, Colorado butterfly plant
  Oenothera depressa ssp. strigosa (Rydb.) Roy L. Taylor & MacBryde -- not accepted
  Oenothera latifolia (Rydb.) Munz -- not accepted -- mountain evening primrose, mountain evening-primrose, mountain eveningprimrose
  Oenothera longissima Rydb. -- accepted -- longstem evening primrose, longstem evening-primrose, longstem eveningprimrose
  Oenothera longissima var. longissima Rydb. -- not accepted
  Oenothera ornata (A. Nelson) Rydb. -- not accepted
  Oenothera pallida ssp. latifolia (Rydb.) Munz -- accepted -- mountain evening primrose
  Oenothera strigosa (Rydb.) Mack. & Bush -- not accepted
  Oenothera tetragona var. latifolia (Rydb.) Fernald -- not accepted
  Oenothera villosa ssp. strigosa (Rydb.) W. Dietr. & P.H. Raven -- accepted -- hairy evening primrose, hairy evening-primrose, hairy eveningprimrose
  Oenothera villosa var. strigosa (Rydb.) Dorn -- not accepted
  Oglifa californica (Nutt.) Rydb. -- not accepted
  Oligoneuron canescens Rydb. -- not accepted
  Oligoneuron riddellii (Frank ex Riddell) Rydb. -- not accepted -- Riddell's goldenrod
  Ophrys caurina (Piper) Rydb. -- not accepted
  Opulaster alabamensis Rydb. -- not accepted
  Opulaster australis Rydb. -- not accepted
  Opulaster intermedius Rydb. -- not accepted
  Opulaster stellatus Rydb. -- not accepted
  Orbexilum gracile (Torr. & A. Gray) Rydb. -- not accepted
  Orbexilum macrophyllum (Rowlee ex Small) Rydb. -- accepted -- bigleaf scurfpea, largeleaf leather-root
  Orbexilum onobrychis (Nutt.) Rydb. -- accepted -- French-grass
  Orbexilum pedunculatum (Mill.) Rydb. -- accepted -- Sampson's snakeroot
  Orbexilum pedunculatum var. pedunculatum (Mill.) Rydb. -- accepted -- babyroot scurfpea, Sampson's snakeroot
  Orbexilum simplex (Nutt. ex Torr. & A. Gray) Rydb. -- accepted -- simple scurfpea, singlestem leather-root
  Orbexilum stipulatum (Torr. & A. Gray) Rydb. -- accepted -- largestipule leather-root
  Orbexilum virgatum (Nutt.) Rydb. -- accepted -- pineland leather-root
  Oreobatus Rydb. -- not accepted
  Oreobatus deliciosus (Torr.) Rydb. -- not accepted
  Oreobatus neomexicanus (A. Gray) Rydb. -- not accepted
  Oreocarya pustulosa Rydb. -- not accepted
  Oreochrysum Rydb. -- accepted -- goldenrod
  Oreochrysum parryi (A. Gray) Rydb. -- accepted -- Parry's goldenrod
  Oreoxis macdougalii (J.M. Coult. & Rose) Rydb. -- not accepted
  Orobanche californica var. corymbosa (Rydb.) Munz -- not accepted
  Orobanche corymbosa (Rydb.) Ferris -- accepted -- flat-top broomrape, Rydberg's broomrape
  Orobanche corymbosa ssp. corymbosa (Rydb.) Ferris -- accepted -- flat-top broomrape, flattop broomrape
  Orophaca aretioides (M.E. Jones) Rydb. -- not accepted
  Orophaca tridactylica (A. Gray) Rydb. -- not accepted
  Osmorhiza aristata (Thunb.) Rydb. -- accepted
  Othake sphacelata (Nutt. ex Torr.) Rydb. -- not accepted
  Oxalis coloradensis Rydb. -- not accepted
  Oxybaphus lanceolatus (Rydb.) Standl. -- not accepted
  Oxycoccus intermedius (A. Gray) Rydb. -- not accepted
  Oxytropis alpicola (Rydb.) M.E. Jones -- not accepted
  Oxytropis besseyi (Rydb.) Blank. -- accepted -- Bessey's locoweed, red crazyweed
  Oxytropis besseyi var. argophylla (Rydb.) Barneby -- accepted -- Montana locoweed
  Oxytropis besseyi var. besseyi (Rydb.) Blank. -- accepted -- Bessey's locoweed
  Oxytropis campestris ssp. varians (Rydb.) Cody -- not accepted
  Oxytropis campestris var. varians (Rydb.) Barneby -- accepted -- field locoweed
  Oxytropis lagopus var. atropurpurea (Rydb.) Barneby -- accepted -- haresfoot locoweed
  Oxytropis leucantha var. depressa (Rydb.) B. Boivin -- not accepted
  Oxytropis leucantha var. depressus (Rydb.) B. Boivin -- not accepted
  Oxytropis nana var. argophylla (Rydb.) Isely -- not accepted -- Montana crazyweed
  Oxytropis nana var. besseyi (Rydb.) Isely -- not accepted -- Bessey's pointvetch
  Oxytropis patens (Rydb.) A. Nelson -- not accepted
  Oxytropis varians (Rydb.) K. Schum. -- not accepted
  Oxytropis villosa (Rydb.) K. Schum. -- not accepted
  Ozomelis anomala (Piper) Rydb. -- not accepted
  Ozomelis diversifolia (Greene) Rydb. -- not accepted
  Ozomelis micrantha (Piper) Rydb. -- not accepted
  Ozomelis stauropetala (Piper) Rydb. -- not accepted
  Ozomelis trifida (Graham) Rydb. -- not accepted
  Packera crocata (Rydb.) W.A. Weber & Á. Löve -- accepted -- saffron ragwort
  Packera millelobata (Rydb.) W.A. Weber & Á. Löve -- accepted -- Uinta ragwort
  Packera oodes (Rydb.) W.A. Weber -- not accepted
  Packera pseudaurea (Rydb.) W.A. Weber & Á. Löve -- accepted -- falsegold groundsel
  Packera pseudaurea var. pseudaurea (Rydb.) W.A. Weber & Á. Löve -- accepted -- falsegold groundsel
  Packera sanguisorboides (Rydb.) W.A. Weber & Á. Löve -- accepted -- burnet ragwort
  Packera tridenticulata (Rydb.) W.A. Weber & Á. Löve -- accepted -- threetooth ragwort
  Palafoxia macrolepis (Rydb.) Cory -- not accepted
  Palafoxia rosea var. macrolepis (Rydb.) B.L. Turner & Morris -- not accepted -- rosy palafox
  Palafoxia texana var. macrolepis (Rydb.) Shinners -- not accepted
  Paneion interius (Rydb.) Lunell -- not accepted
  Paneion pratericola (Rydb. & Nash) Lunell -- not accepted
  Panicularia rigida (Nash) Rydb. -- not accepted
  Panicum capillare var. occidentale Rydb. -- not accepted
  Papaver pygmaeum Rydb. -- accepted -- alpine poppy
  Papaver radicatum var. pygmaeum (Rydb.) S.L. Welsh -- not accepted
  Parietaria obtusa Rydb. ex Small -- not accepted
  Parietaria occidentalis Rydb. -- not accepted
  Parietaria pensylvanica var. obtusa (Rydb. ex Small) Shinners -- not accepted -- Pennsylvania pellitory
  Parnassia cirrata var. intermedia (Rydb.) P.K. Holmgren & N.H. Holmgren -- accepted -- fringed grass of Parnassus
  Parnassia fimbriata var. intermedia (Rydb.) C.L. Hitchc. -- not accepted -- fringed grass of Parnassus, intermediate parnassia
  Parnassia floridana Rydb. -- not accepted
  Parnassia intermedia Rydb. -- not accepted
  Parnassia montanensis Fernald & Rydb. -- not accepted
  Parnassia palustris var. montanensis (Fernald & Rydb. ex Rydb.) C.L. Hitchc. -- not accepted -- mountain grass of Parnassus, northern grass-of-Parnassus
  Paronychia wardii Rydb. -- not accepted
  Parosela alopecuroides (Willd.) Rydb. -- not accepted
  Parosela carnescens Rydb. -- not accepted
  Parosela floridana Rydb. -- not accepted
  Parosela longipila Rydb. -- not accepted
  Parosela mollissima Rydb. -- not accepted
  Parrya platycarpa Rydb. -- not accepted
  Pascopyrum smithii (Rydb.) Á. Löve -- not accepted -- pubescent wheatgrass, western wheatgrass
  Pascopyrum smithii (Rydb.) Barkworth & D.R. Dewey -- accepted
  Pectiantia breweri (A. Gray) Rydb. -- not accepted
  Pectiantia ovalis (Greene) Rydb. -- not accepted
  Pectiantia pentandra (Hook.) Rydb. -- not accepted
  Pectis cylindrica (Fernald) Rydb. -- accepted -- Sonoran chinchweed, Sonoran cinchweed
  Pectis multisetosa Rydb. -- not accepted
  Pedicularis bracteosa var. siifolia (Rydb.) Cronquist -- accepted -- smoothflower lousewort
  Pedicularis contorta var. ctenophora (Rydb.) A. Nelson & J.F. Macbr. -- accepted -- coiled lousewort
  Pedicularis contorta var. tenophora (Rydb.) A. Nelson & J.F. Macbr. -- not accepted
  Pedicularis ctenophora Rydb. -- not accepted
  Pedicularis cystopteridifolia Rydb. -- accepted -- fernleaved pedicularis
  Pedicularis hallii Rydb. -- not accepted
  Pedicularis lunata Rydb. -- not accepted
  Pedicularis montanensis Rydb. -- not accepted
  Pedicularis siifolia Rydb. -- not accepted
  Pediomelum Rydb. -- accepted -- breadroot, Indian breadroot, scurfpea
  Pediomelum brachypus Rydb. -- not accepted
  Pediomelum californicum (S. Watson) Rydb. -- accepted -- California Indian breadroot
  Pediomelum canescens (Michx.) Rydb. -- accepted -- buckroot
  Pediomelum castoreum (S. Watson) Rydb. -- accepted -- Beaver Dam scurfpea, Beaver Indian breadroot
  Pediomelum cuspidatum (Pursh) Rydb. -- accepted -- largebract Indian breadroot, tallbread scurfpea
  Pediomelum cyphocalyx (A. Gray) Rydb. -- accepted -- turniproot
  Pediomelum esculentum (Pursh) Rydb. -- accepted -- breadroot scurfpea, Indian breadroot, large Indian breadroot
  Pediomelum humile Rydb. -- accepted -- Rydberg's Indian breadroot, Rydberg's scurpea
  Pediomelum hypogaeum (Nutt.) Rydb. -- accepted -- scurfpea, subterranean Indian breadroot
  Pediomelum hypogaeum var. hypogaeum (Nutt.) Rydb. -- accepted -- subterranean Indian breadroot
  Pediomelum megalanthum (Wooton & Standl.) Rydb. -- accepted -- Intermountain Indian breadroot, large-flowered Indian breadroot
  Pediomelum megalanthum var. megalanthum (Wooton & Standl.) Rydb. -- accepted -- Intermountain Indian breadroot
  Pediomelum megalanthum var. retrorsum (Rydb.) J.W. Grimes -- accepted -- Intermountain Indian breadroot
  Pediomelum mephiticum (S. Watson) Rydb. -- accepted -- skunktop
  Pediomelum pentaphyllum (L.) Rydb. -- accepted -- Chihuahua scurfpea, small Indian breadroot
  Pediomelum reverchonii (S. Watson) Rydb. -- accepted -- rock Indian breadroot, rock scurfpea
  Pediomelum rhombifolium (Torr. & A. Gray) Rydb. -- accepted -- Gulf Indian breadroot, roundleaf scurfpea
  Pediomelum subacaule (Torr. & A. Gray) Rydb. -- accepted -- whiterim scurfpea
  Pediomelum subacaulis (Torr. & A. Gray) Rydb. -- not accepted
  Pediomelum subulatum (Bush) Rydb. -- not accepted
  Pediomelum trinervatum Rydb. -- not accepted
  Pellaea occidentalis (E.E. Nelson) Rydb. -- not accepted
  Penstemon angustifolius var. caudatus (A. Heller) Rydb. -- accepted -- broadbeard beardtongue
  Penstemon aridus Rydb. -- accepted -- stiffleaf penstemon
  Penstemon attenuatus ssp. pseudoprocerus (Rydb.) D.D. Keck -- not accepted
  Penstemon attenuatus var. pseudoprocerus (Rydb.) Cronquist -- accepted -- small penstemon
  Penstemon brandegeei (Porter) Rydb. -- not accepted
  Penstemon cyathophorus Rydb. -- accepted -- Northpark penstemon, sagebrush beardtongue
  Penstemon diphyllus Rydb. -- accepted -- twoleaf beardtongue
  Penstemon leonardii Rydb. -- accepted -- Leonard's beardtongue, Leonard's penstemon
  Penstemon leonardii var. leonardii Rydb. -- accepted -- Leonard's beardtongue
  Penstemon pachyphyllus A. Gray ex Rydb. -- accepted -- thickleaf beardtongue, thickleaf penstemon
  Penstemon pachyphyllus var. pachyphyllus A. Gray ex Rydb. -- accepted -- thickleaf beardtongue
  Penstemon platyphyllus Rydb. -- accepted -- broadleaf beardtongue, broadleaf penstemon
  Penstemon puberulentus Rydb. -- not accepted
  Penstemon strictiformis Rydb. -- accepted -- Mancos penstemon, stiff penstemon
  Penstemon strictus ssp. strictiformis (Rydb.) D.D. Keck -- not accepted
  Penstemon subglaber Rydb. -- accepted -- smooth penstemon
  Penstemon suffrutescens Rydb. -- not accepted
  Penstemon thompsoniae (A. Gray) Rydb. -- accepted -- Thompson's beardtongue, Thompson's penstemon
  Penstemon thompsoniae ssp. thompsoniae (A. Gray) Rydb. -- not accepted -- Thompson's beardtongue, Thompson's penstemon
  Penstemon triphyllus ssp. diphyllus (Rydb.) D.D. Keck -- not accepted
  Penstemon unilateralis Rydb. -- not accepted -- oneside penstemon
  Penstemon virens Pennell ex Rydb. -- accepted -- Front Range beardtongue
  Penstemon wilcoxii Rydb. -- accepted -- Wilcox's penstemon
  Peramium ophioides (Fernald) Rydb. -- not accepted
  Perityle ciliata (L.H. Dewey) Rydb. -- accepted -- fringed rockdaisy, hairy rock-daisy
  Perityle gracilis (M.E. Jones) Rydb. -- accepted -- grass-leaf rockdaisy, grassleaf rockdaisy, grasslike rockdaisy, three-lobed rockdaisy
  Perityle rotundata (Rydb.) Shinners -- not accepted
  Perityle spilanthoides (Sch. Bip.) Rydb. -- not accepted
  Petalostemon adenopodus (Rydb.) Wemple -- not accepted
  Petalostemon mollis Rydb. -- not accepted
  Petalostemon pilosulus Rydb. -- not accepted
  Petalostemon purpureus (Vent.) Rydb. -- not accepted
  Petalostemon purpureus var. mollis (Rydb.) A. Nelson -- not accepted
  Petasites alaskanus Rydb. -- not accepted
  Petasites corymbosus (R. Br.) Rydb. -- not accepted
  Petasites hookerianus (Nutt.) Rydb. -- not accepted
  Petasites hyperboreus Rydb. -- not accepted
  Petrophyton Rydb. -- not accepted -- rock spirea, rockmat, rockspirea
  Petrophyton acuminatum Rydb. -- not accepted -- big arroyo rockmat
  Petrophyton caespitosum (Nutt.) Rydb. -- not accepted -- mat rockspirea, rockspirea, tufted rockmat
  Petrophyton caespitosum ssp. acuminatum (Rydb.) Munz -- not accepted
  Petrophyton caespitosum var. caespitosum (Nutt.) Rydb. -- not accepted -- mat rockspirea, Rocky Mountain rockmat, Rocky Mountain rockspirea
  Petrophyton cinerascens (Piper) Rydb. -- not accepted -- halfshrub rockmat
  Petrophyton hendersonii (Canby) Rydb. -- not accepted -- Olympic Mountain rockmat
  Petrophytum (Nutt. ex Torr. & A. Gray) Rydb. -- accepted -- rockspirea
  Petrophytum acuminatum Rydb. -- not accepted -- big arroyo rockmat
  Petrophytum caespitosum (Nutt.) Rydb. -- accepted -- mat rockspirea
  Petrophytum caespitosum ssp. acuminatum (Rydb.) Munz -- accepted
  Petrophytum caespitosum ssp. caespitosum (Nutt.) Rydb. -- accepted -- rock spiraea
  Petrophytum caespitosum var. caespitosum (Nutt.) Rydb. -- not accepted -- mat rockspirea
  Petrophytum cinerascens (Piper) Rydb. -- accepted -- chelan rockmat, halfshrub rockmat
  Petrophytum hendersonii (Canby) Rydb. -- accepted -- Olympic Mountain rockmat
  Phaca americana (Hook.) Rydb. ex Britton & A. Br. -- not accepted
  Phaca bodinii (E. Sheld.) Rydb. -- not accepted
  Phaca intonsa (E. Sheld.) Rydb. ex Small -- not accepted
  Phaca obcordata (Elliott) Rydb. ex Small -- not accepted
  Phacelia alba Rydb. -- accepted -- white phacelia, white scorpion-weed, white scorpionweed
  Phacelia alpina Rydb. -- not accepted
  Phacelia ciliosa (Rydb.) Rydb. -- not accepted
  Phacelia hastata var. alpina (Rydb.) Cronquist -- not accepted
  Phacelia hastata var. leptosepala (Rydb.) Cronquist -- not accepted
  Phacelia leptosepala Rydb. -- accepted -- narrowsepal phacelia
  Phacelia leucophylla var. alpina (Rydb.) Dundas -- not accepted
  Phacelia lyallii (A. Gray) Rydb. -- accepted -- alpine phacelia
  Phacelia lyonii (A. Gray) Rydb. -- accepted -- Lyon's phacelia
  Phacelia neomexicana var. alba (Rydb.) Brand -- not accepted
  Phacelia sericea ssp. ciliosa (Rydb.) G.W. Gillett -- accepted -- purplefringe, silky phacelia
  Phacelia sericea var. ciliosa Rydb. -- not accepted
  Philadelphus argenteus Rydb. -- not accepted -- silver mock orange, silver mockorange
  Philadelphus lewisii var. angustifolius (Rydb.) S.Y. Hu -- not accepted -- Lewis' mockorange
  Philadelphus lewisii var. helleri (Rydb.) S.Y. Hu -- not accepted -- Heller's mockorange
  Philadelphus lewisii var. platyphyllus (Rydb.) S.Y. Hu -- not accepted -- Lewis' mockorange
  Philadelphus microphyllus ssp. argenteus (Rydb.) C.L. Hitchc. -- not accepted
  Philadelphus microphyllus ssp. pumilus (Rydb.) C.L. Hitchc. -- not accepted
  Philadelphus microphyllus ssp. stramineus (Rydb.) C.L. Hitchc. -- not accepted
  Philadelphus microphyllus var. argenteus (Rydb.) Kearney & Peebles -- not accepted
  Philadelphus microphyllus var. minutus (Rydb.) S.Y. Hu -- not accepted -- littleleaf mockorange
  Philadelphus microphyllus var. stramineus (Rydb.) Henrickson -- accepted -- littleleaf mock orange
  Philadelphus occidentalis var. minutus (Rydb.) S.Y. Hu -- not accepted -- Grand Canyon mock orange, western mock orange, western mockorange
  Philadelphus palmeri Rydb. -- accepted -- Palmer's mock orange, Palmer's mockorange
  Philadelphus pumilus Rydb. -- not accepted -- dwarf mock orange
  Philadelphus pumilus var. pumilus Rydb. -- not accepted -- dwarf mock orange
  Philadelphus stramineus Rydb. -- not accepted
  Philotria angustifolia (Muhl.) Britton ex Rydb. -- not accepted
  Philotria linearis Rydb. -- not accepted
  Philotria nuttallii (Planch.) Rydb. -- not accepted
  Phlox albomarginata ssp. diapensioides (Rydb.) Wherry -- accepted -- whitemargin phlox
  Phlox alyssifolia ssp. collina (Rydb.) Wherry -- accepted -- alyssumleaf phlox
  Phlox diffusa ssp. scleranthifolia (Rydb.) Wherry -- accepted -- spreading phlox
  Phlox multiflora ssp. costata (Rydb.) Wherry -- not accepted
  Phlox scleranthifolia Rydb. -- not accepted
  Phyllodoce X intermedia (Hook.) Rydb. (pro sp.) -- accepted -- hybrid mountainheath
  Physalis angulata var. pendula (Rydb.) Waterf. -- not accepted
  Physalis arenicola var. ciliosa (Rydb.) Waterf. -- not accepted
  Physalis barbadensis var. obscura (Michx.) Rydb. -- not accepted
  Physalis carpenteri Riddell ex Rydb. -- accepted -- Carpenter's groundcherry
  Physalis ciliosa Rydb. -- not accepted
  Physalis comata Rydb. -- not accepted
  Physalis crassifolia var. versicolor (Rydb.) Waterf. -- accepted -- yellow nightshade groundcherry
  Physalis floridana Rydb. -- not accepted
  Physalis foetens var. neomexicana (Rydb.) Waterf. -- not accepted
  Physalis hederifolia var. comata (Rydb.) Waterf. -- accepted -- heartleaf groundcherry, ivyleaf groundcherry
  Physalis heterophylla var. ambigua (A. Gray) Rydb. -- not accepted
  Physalis heterophylla var. nyctaginea (Dunal) Rydb. -- not accepted
  Physalis intermedia Rydb. -- not accepted
  Physalis macrophysa Rydb. -- not accepted
  Physalis mollis var. parvifolia Rydb. -- not accepted
  Physalis neomexicana Rydb. -- accepted
  Physalis pendula Rydb. -- not accepted
  Physalis pruinosa sensu Rydb. -- not accepted
  Physalis rotundata Rydb. -- not accepted
  Physalis sinuata Rydb. -- not accepted
  Physalis subulata Rydb. -- accepted -- Chihuahuan groundcherry
  Physalis subulata var. neomexicana (Rydb.) Waterf. ex Kartesz & Gandhi -- not accepted -- Chihuahuan groundcherry, New Mexican groundcherry
  Physalis subulata var. subulata Rydb. -- accepted -- Chihuahuan groundcherry
  Physalis versicolor Rydb. -- not accepted
  Physalis virginiana var. texana (Rydb.) Waterf. -- accepted -- Texan groundcherry
  Physalis viscosa var. maritima (M.A. Curtis) Rydb. -- not accepted
  Physaria acutifolia Rydb. -- accepted -- sharpleaf twinpod
  Physaria acutifolia var. acutifolia Rydb. -- not accepted -- sharpleaf twinpod, southern twinpod
  Physaria brassicoides Rydb. -- accepted -- double twinpod
  Physaria floribunda Rydb. -- accepted -- pointtip twinpod
  Physaria floribunda ssp. floribunda Rydb. -- accepted -- pointtip twinpod
  Physaria floribunda var. floribunda Rydb. -- not accepted -- pointtip twinpod
  Physaria kingii ssp. utahensis (Rydb.) O'Kane -- accepted -- Utah bladderpod
  Physaria lanata (A. Nelson) Rydb. -- not accepted
  Physaria ovalifolia (Rydb.) O'Kane & Al-Shehbaz -- accepted -- roundleaf bladderpod
  Physaria ovalifolia ssp. ovalifolia (Rydb.) O'Kane & Al-Shehbaz -- accepted -- roundleaf bladderpod
  Physaria reediana ssp. spatulata (Rydb.) O'Kane & Al-Shehbaz -- not accepted
  Physaria spatulata (Rydb.) Grady & O'Kane -- accepted -- alpine bladderpod
  Physaria vitulifera Rydb. -- accepted -- roundtip twinpod
  Physocarpus bracteatus (Rydb.) Rehder -- accepted
  Physocarpus intermedius (Rydb.) C.K. Schneid. -- accepted -- Atlantic ninebark
  Physocarpus opulifolius var. intermedius (Rydb.) B.L. Rob. -- not accepted -- Atlantic ninebark
  Picradenia helenioides Rydb. -- not accepted
  Picradeniopsis Rydb. ex Britton -- accepted -- bahia
  Picradeniopsis oppositifolia (Nutt.) Rydb. ex Britton -- accepted -- opposite-leaf false bahia, oppositeleaf bahia, plains bahia
  Picradeniopsis woodhousei (A. Gray) Rydb. -- accepted -- Woodhouse's bahia, Woodhouse's false bahia
  Pilea fontana (Lunell) Rydb. -- accepted -- lesser clearweed
  Pilea opaca (Lunell) Rydb. -- not accepted
  Pilosella novae-angliae Rydb. -- not accepted
  Pilosella richardsonii Rydb. -- not accepted
  Piperia Rydb. -- not accepted -- rein orchid
  Piperia cooperi (S. Watson) Rydb. -- not accepted -- Cooper's rein orchid
  Piperia elegans (Lindl.) Rydb. -- not accepted -- elegant piperia
  Piperia elegans ssp. elegans (Lindl.) Rydb. -- not accepted -- elegant piperia
  Piperia elongata Rydb. -- not accepted -- denseflower rein orchid
  Piperia elongata ssp. elongata Rydb. -- not accepted -- denseflower rein orchid
  Piperia lancifolia Rydb. -- not accepted
  Piperia leptopetala Rydb. -- not accepted -- narrow-petal rein orchid
  Piperia maritima Rydb. -- not accepted
  Piperia michaeli (Greene) Rydb. -- not accepted
  Piperia michaelii (Greene) Rydb. -- not accepted -- Michael's piperia
  Piperia multiflora Rydb. -- not accepted
  Piperia unalascensis (Spreng.) Rydb. -- not accepted -- Alaska bog orchid, Alaska rein orchid, Alaskan rein-orchid, Piperia de Alaska, pipérie d'Unalaska, slender-spire orchid
  Pisophaca flexuosa (Douglas ex Hook.) Rydb. -- not accepted
  Plantago septata E. Morris ex Rydb. -- not accepted
  Platanthera elegans ssp. maritima (Rydb.) R.M. Bateman -- accepted
  Platanthera elongata (Rydb.) R.M. Bateman -- accepted
  Platanthera hyperborea var. purpurascens (Rydb.) Luer -- not accepted
  Platanthera leptopetala (Rydb.) R.M. Bateman -- accepted
  Platanthera purpurascens (Rydb.) Sheviak & W.F. Jenn. -- accepted -- purple-petal bog orchid
  Platanthera sparsiflora var. ensiflora (Rydb.) Luer -- not accepted
  Platanthera sparsiflora var. ensifolia (Rydb.) Luer -- not accepted -- canyon bog orchid, sparse-flowered bog orchid
  Platanthera tipuloides var. behringiana (Rydb.) Hultén -- accepted -- Aleutian bog orchid
  Platanthera X media (Rydb.) Luer (pro. sp.) -- not accepted -- bog orchid
  Platyschkuhria Rydb. -- accepted -- basindaisy, platyschkuhria
  Platyschkuhria integrifolia (A. Gray) Rydb. -- accepted -- basin daisy, basindaisy, desert basindaisy, oblongleaf bahia, oblongleaf basindaisy
  Platyschkuhria integrifolia var. integrifolia (A. Gray) Rydb. -- not accepted -- basindaisy
  Platyschkuhria oblongifolia (A. Gray) Rydb. -- not accepted
  Plectritis macroptera (Suksd.) Rydb. -- not accepted
  Pleiacanthus Rydb. -- accepted
  Pleiacanthus spinosus (Nutt.) Rydb. -- accepted -- thorn skeletonweed
  Poa callichroa Rydb. -- not accepted
  Poa callida Rydb. -- not accepted
  Poa confusa Rydb. -- not accepted
  Poa curta Rydb. -- not accepted -- Wasatch bluegrass
  Poa helleri Rydb. -- not accepted
  Poa interior Rydb. -- accepted -- inland bluegrass
  Poa laxa var. occidentalis Vasey ex Rydb. & Shear -- not accepted
  Poa macroclada Rydb. -- not accepted -- largesprout bluegrass
  Poa nematophylla Rydb. -- not accepted
  Poa nemoralis ssp. interior (Rydb.) W.A. Weber -- not accepted -- inland bluegrass
  Poa nemoralis var. interior (Rydb.) Butters & Abbe -- not accepted
  Poa occidentalis (Vasey) Rydb. -- not accepted
  Poa overi Rydb. -- not accepted
  Poa phoenicea Rydb. -- not accepted
  Poa plattensis Rydb. -- not accepted
  Poa platyphylla Nash & Rydb. -- not accepted
  Poa pratensiformis Rydb. -- not accepted
  Poa pratensis var. pseudopratensis (Scribn. & Rydb.) M.E. Jones -- not accepted
  Poa pratericola Rydb. & Nash -- not accepted
  Poa pseudopratensis Scribn. & Rydb. -- not accepted
  Poa pudica Rydb. -- not accepted
  Poa scaberrima Rydb. -- not accepted
  Poa subpurpurea Rydb. -- not accepted
  Poa subreflexa Rydb. -- not accepted
  Poa subtrivialis Rydb. -- not accepted
  Poa tricholepis Rydb. -- not accepted
  Poa truncata Rydb. -- not accepted
  Poa X nematophylla Rydb. (pro sp.) -- accepted
  Polemonium columbianum Rydb. -- not accepted
  Polemonium delicatum Rydb. -- not accepted
  Polemonium foliosissimum ssp. robustum (Rydb.) Brand -- not accepted
  Polemonium grayanum Rydb. -- not accepted
  Polemonium intermedium (Brand) Rydb. -- not accepted
  Polemonium pulcherrimum ssp. delicatum (Rydb.) Brand -- accepted -- beautiful Jacob's-ladder, skunkweed Jacob's-ladder
  Polemonium pulcherrimum var. delicatum (Rydb.) Cronquist -- not accepted
  Polygonum paronychioides Small ex Rydb. -- not accepted -- knotweed
  Polygonum unifolium Small ex Rydb. -- not accepted
  Populus deltoides var. occidentalis Rydb. -- not accepted
  Populus occidentalis (Rydb.) Britton ex Rydb. -- not accepted
  Populus X acuminata Rydb. (pro sp.) -- accepted -- lanceleaf cottonwood
  Porophyllum leiocarpum (Urb.) Rydb. -- accepted -- yerba de peo
  Potamogeton interior Rydb. -- not accepted
  Potamogeton richardsoni (A. Benn.) Rydb. -- not accepted
  Potamogeton richardsonii (A. Benn.) Rydb. -- accepted -- red-head pondweed, Richardson pondweed, Richardson's pondweed
  Potentilla alaskana Rydb. -- not accepted
  Potentilla angustata Rydb. -- not accepted
  Potentilla arguta ssp. convallaria (Rydb.) D.D. Keck -- not accepted -- cream cinquefoil
  Potentilla arguta var. convallaria (Rydb.) Th. Wolf -- not accepted
  Potentilla argyrea Rydb. -- not accepted
  Potentilla argyrocoma (Rydb.) Jeps. -- not accepted
  Potentilla atrorubens Rydb. -- not accepted
  Potentilla atrovirens Rydb. -- not accepted
  Potentilla bakeri Rydb. -- not accepted
  Potentilla bicrenata Rydb. -- accepted
  Potentilla blasckeana var. permollis (Rydb.) Th. Wolf -- not accepted
  Potentilla bruceae Rydb. -- accepted -- Bruce's cinquefoil
  Potentilla brunnescens Rydb. -- not accepted
  Potentilla camporum Rydb. -- not accepted
  Potentilla caruifolia (Rydb. ex Howell) Crum -- not accepted
  Potentilla concinna var. bicrenata (Rydb.) S.L. Welsh & B.C. Johnst. -- not accepted -- elegant cinquefoil, red cinquefoil
  Potentilla concinna var. divisa Rydb. -- accepted
  Potentilla concinna var. macounii (Rydb.) C.L. Hitchc. -- not accepted
  Potentilla concinna var. modesta (Rydb.) S.L. Welsh & B.C. Johnst. -- not accepted -- red cinquefoil
  Potentilla concinna var. proxima (Rydb.) S.L. Welsh & B.C. Johnst. -- accepted -- elegant cinquefoil, red cinquefoil
  Potentilla concinna var. rubripes (Rydb.) C.L. Hitchc. -- not accepted
  Potentilla convallaria Rydb. -- not accepted
  Potentilla decurrens (S. Watson) Rydb. -- not accepted
  Potentilla diversifolia var. perdissecta (Rydb.) C.L. Hitchc. -- not accepted -- mountain-meadow cinquefoil, mountainmeadow cinquefoil
  Potentilla divisa (Rydb.) Rydb. -- not accepted
  Potentilla douglasii var. pseudocapitata (Rydb. ex Howell) Jeps. -- not accepted -- pinewoods horkelia
  Potentilla drummondii ssp. bruceae (Rydb.) D.D. Keck -- not accepted -- Drummond's cinquefoil
  Potentilla drummondii var. bruceae (Rydb.) N.H. Holmgren -- not accepted
  Potentilla elmeri Rydb. -- not accepted
  Potentilla etomentosa Rydb. -- not accepted
  Potentilla etomentosa var. hallii (Rydb.) Abrams -- not accepted
  Potentilla fastigiata var. permollis (Rydb.) Soják -- not accepted
  Potentilla flabelliformis var. ctenophora Rydb. -- not accepted
  Potentilla glabella Rydb. -- not accepted
  Potentilla glabrella Rydb. -- not accepted
  Potentilla glandulosa ssp. arizonica (Rydb.) D.D. Keck -- not accepted -- Arizona cinquefoil
  Potentilla glandulosa ssp. glabrata (Rydb.) D.D. Keck -- not accepted -- sticky cinquefoil
  Potentilla glandulosa ssp. micropetala (Rydb.) D.D. Keck -- not accepted -- smallpetal cinquefoil
  Potentilla glandulosa ssp. pseudorupestris (Rydb.) D.D. Keck -- not accepted -- sticky cinquefoil
  Potentilla glandulosa var. intermedia (Rydb.) C.L. Hitchc. -- not accepted
  Potentilla glandulosa var. micropetala (Rydb.) S.L. Welsh & B.C. Johnst. -- not accepted
  Potentilla glandulosa var. pseudorupestris (Rydb.) Breitung -- not accepted
  Potentilla glaucophylla var. perdissecta (Rydb.) Soják -- accepted -- mountainmeadow cinquefoil
  Potentilla gordonii var. chaetophora (Rydb.) Jeps. -- not accepted
  Potentilla gracilis var. brunnescens (Rydb.) C.L. Hitchc. -- not accepted -- sagebrush cinquefoil, slender cinquefoil
  Potentilla gracilis var. ctenophora (Rydb.) B. Boivin -- not accepted
  Potentilla gracilis var. elmeri (Rydb.) Jeps. -- accepted
  Potentilla gracilis var. filipes (Rydb.) B. Boivin -- not accepted
  Potentilla gracilis var. hallii (Rydb.) Th. Wolf -- not accepted
  Potentilla gracilis var. permollis (Rydb.) C.L. Hitchc. -- not accepted
  Potentilla hippiana var. argyrea (Rydb.) B. Boivin -- not accepted -- woolly cinquefoil
  Potentilla hispidula (Rydb.) Jeps. -- not accepted
  Potentilla kelloggii var. puberula (Rydb.) Hoover -- not accepted
  Potentilla klamathensis Rydb. -- not accepted
  Potentilla langeana Rydb. -- not accepted
  Potentilla lasiodonta Rydb. -- accepted -- Sandhills cinquefoil
  Potentilla leucocarpa Rydb. -- not accepted
  Potentilla lindleyi var. puberula (Rydb.) J.T. Howell -- not accepted
  Potentilla litoralis Rydb. -- accepted -- Pennsylvania cinquefoil
  Potentilla longipedunculata Rydb. -- not accepted
  Potentilla lycopodioides var. megalopetala (Rydb.) J.T. Howell -- not accepted
  Potentilla lycopodioides var. scandularis (Rydb.) J.T. Howell -- not accepted
  Potentilla macounii Rydb. -- accepted -- Macoun's cinquefoil
  Potentilla macropetala Rydb. -- not accepted
  Potentilla millefolia Rydb. -- accepted -- cutleaf cinquefoil, manyleaf cinquefoil
  Potentilla millefolia var. klamathensis (Rydb.) Jeps. -- not accepted -- Klamath cinquefoil
  Potentilla millefolia var. millefolia Rydb. -- not accepted -- cutleaf cinquefoil
  Potentilla minutifolia Rydb. -- not accepted
  Potentilla modesta Rydb. -- accepted -- Uintah cinquefoil
  Potentilla multisecta (S. Watson) Rydb. -- accepted -- alpine cinquefoil, featherleaf cinquefoil
  Potentilla nelsoniana Rydb. -- not accepted
  Potentilla nipharga Rydb. -- not accepted
  Potentilla oblanceolata Rydb. -- accepted -- New Mexico cinquefoil
  Potentilla paucijuga Rydb. -- accepted -- La Sal cinquefoil
  Potentilla pectinisecta Rydb. -- not accepted -- coilleaf cinquefoil, comb-leaf cinquefoil, combleaf cinquefoil
  Potentilla pectinisecta var. comosa (Rydb.) Soják -- not accepted
  Potentilla pedersenii (Rydb.) Rydb. -- accepted
  Potentilla pensylvanica var. atrovirens (Rydb.) Th. Wolf -- not accepted -- Pennsylvania cinquefoil
  Potentilla pensylvanica var. litoralis (Rydb.) B. Boivin -- not accepted -- Pennsylvania cinquefoil
  Potentilla pensylvanica var. paucijuga (Rydb.) S.L. Welsh & B.C. Johnst. -- not accepted -- Pennsylvania cinquefoil
  Potentilla perdissecta Rydb. -- not accepted
  Potentilla permollis Rydb. -- not accepted
  Potentilla plattensis var. klamathensis (Rydb.) Jeps. -- not accepted
  Potentilla plattensis var. millefolia (Rydb.) Jeps. -- not accepted
  Potentilla platyloba Rydb. -- not accepted
  Potentilla propinqua (Rydb.) Rydb. -- not accepted
  Potentilla proxima Rydb. -- not accepted
  Potentilla pseudorupestris Rydb. -- not accepted
  Potentilla pseudosericea Rydb. -- accepted -- silky cinquefoil
  Potentilla pseudosericea auct. non Rydb. -- not accepted
  Potentilla purpurascens var. congdonis (Rydb.) Jeps. -- not accepted
  Potentilla quinquefolia (Rydb.) Rydb. -- not accepted
  Potentilla ramulosa Rydb. -- not accepted
  Potentilla rectiformis Rydb. -- not accepted
  Potentilla rhomboidea Rydb. -- not accepted
  Potentilla robbinsiana (Lehm.) Oakes ex Rydb. -- accepted -- dwarf mountain cinquefoil, Robbins' cinquefoil
  Potentilla rubricaulis var. paucijuga (Rydb.) Soják -- not accepted
  Potentilla rubricaulis var. pedersenii Rydb. -- not accepted
  Potentilla rubripes Rydb. -- not accepted
  Potentilla rubripes var. saximontana (Rydb.) Th. Wolf -- not accepted
  Potentilla sanguinea Rydb. -- accepted -- scarlet cinquefoil
  Potentilla saximontana Rydb. -- accepted
  Potentilla sericoleuca (Rydb.) J.T. Howell -- not accepted
  Potentilla sierrae-blancae Wooton & Rydb. -- accepted -- Sierra Blanca cinquefoil
  Potentilla subjuga Rydb. -- accepted -- Colorado cinquefoil
  Potentilla subvillosa Rydb. -- not accepted
  Potentilla subviscosa var. ramulosa (Rydb.) Kearney & Peebles -- accepted -- Navajo cinquefoil
  Potentilla thurberi var. atrorubens (Rydb.) Kearney & Peebles -- accepted -- scarlet cinquefoil
  Potentilla thurberi var. sanguinea (Rydb.) Kearney & Peebles -- not accepted -- scarlet cinquefoil
  Potentilla tilingii var. flavescens (Rydb.) J.T. Howell -- not accepted
  Potentilla townsendii Rydb. -- accepted -- Townsend's cinquefoil
  Potentilla truncata (Rydb.) Jeps. -- not accepted
  Potentilla tweedyi (Rydb.) J.T. Howell -- not accepted
  Potentilla versicolor Rydb. -- accepted -- Steens Mountain cinquefoil
  Potentilla viridescens Rydb. -- not accepted
  Potentilla viscidula (Rydb.) Rydb. -- not accepted
  Poteridium occidentale Rydb. -- accepted
  Prenanthella Rydb. -- accepted -- prenanthella
  Prenanthella exigua (A. Gray) Rydb. -- accepted -- brightwhite, feeble prenanthella
  Primula specuicola Rydb. -- accepted -- cave-dwelling primrose
  Prunus corymbulosa Rydb. -- not accepted
  Prunus melanocarpa (A. Nelson) Rydb. -- not accepted
  Prunus pensylvanica ssp. corymbulosa (Rydb.) W. Wight -- not accepted
  Prunus pensylvanica var. corymbulosa (Rydb.) W. Wight -- not accepted
  Psathyrotopsis Rydb. -- accepted
  Pseudobahia Rydb. -- accepted -- sunburst
  Pseudobahia bahiifolia (Benth.) Rydb. -- accepted -- Hartweg's golden sunburst
  Pseudobahia heermannii (Durand) Rydb. -- accepted -- foothill sunburst
  Pseudoclappia Rydb. -- accepted -- false clapdaisy, pseudoclappia
  Pseudoclappia arenaria Rydb. -- accepted -- Trans-Pecos false clapdaisy
  Psilochenia runcinata ssp. hispidulosa (Howell ex Rydb.) W.A. Weber -- not accepted
  Psilostrophe tagetina var. grandiflora (Rydb.) Heiser -- not accepted
  Psilostrophe villosa Rydb. -- accepted -- woolly paperflower
  Psoralea brachypus (Rydb.) Standl. -- not accepted
  Psoralea collina Rydb. -- not accepted
  Psoralea hallii (Rydb.) Jeps. -- not accepted
  Psoralea humilis (Rydb.) J.F. Macbr. -- not accepted
  Psoralea lanceolata var. stenophylla (Rydb.) Toft & S.L. Welsh -- not accepted
  Psoralea lanceolata var. stenostachys (Rydb.) S.L. Welsh -- not accepted
  Psoralea macrostachya var. longiloba (Rydb.) J.F. Macbr. -- not accepted
  Psoralea megalantha var. retrorsa (Rydb.) Kearney & Peebles -- not accepted
  Psoralea mephitica var. retrorsa (Rydb.) Kearney & Peebles -- not accepted
  Psoralea stenostachys Rydb. -- not accepted
  Psoralea tenuiflora var. bigelovii (Rydb.) J.F. Macbr. -- not accepted
  Psoralea tenuiflora var. floribunda (Nutt. ex Torr. & A. Gray) Rydb. -- not accepted
  Psoralea trinervata (Rydb.) Standl. -- not accepted
  Psoralidium Rydb. -- accepted -- breadroot, scurfpea
  Psoralidium argophyllum (Pursh) Rydb. -- not accepted
  Psoralidium batesii Rydb. -- not accepted
  Psoralidium digitatum (Nutt. ex Torr. & A. Gray) Rydb. -- not accepted
  Psoralidium junceum (Eastw.) Rydb. -- accepted -- rush lemonweed
  Psoralidium lanceolatum (Pursh) Rydb. -- accepted -- dune scurfpea, lemon scurfpea, wild lemonweed
  Psoralidium lanceolatum var. stenophyllum (Rydb.) S.L. Welsh -- not accepted
  Psoralidium lanceolatum var. stenostachys (Rydb.) S.L. Welsh -- not accepted
  Psoralidium linearifolium (Torr. & A. Gray) Rydb. -- not accepted
  Psoralidium stenophyllum (Rydb.) Rydb. -- not accepted
  Psoralidium tenuiflorum (Pursh) Rydb. -- accepted -- scurfpea, slimflower scurfpea
  Psorothamnus Rydb. -- accepted -- smokebush
  Psorothamnus emoryi (A. Gray) Rydb. -- accepted -- dyebush, white dalea
  Psorothamnus polydenius (Torr. ex S. Watson) Rydb. -- accepted -- Nevada dalea
  Psorothamnus polydenius var. polydenius (Torr. ex S. Watson) Rydb. -- accepted -- Nevada dalea, Nevada smokebush
  Psorothamnus scoparius (A. Gray) Rydb. -- accepted -- broom dalea
  Psorothamnus scoparus (A. Gray) Rydb. -- not accepted
  Ptilagrostis mongholica ssp. porteri (Rydb.) Barkworth -- not accepted -- Porter's false needlegrass
  Ptilagrostis porteri (Rydb.) W.A. Weber -- accepted -- Porter's false needlegrass
  Ptiloria ramosa Rydb. -- not accepted
  Pyrola borealis Rydb. -- not accepted
  Pyrola gormanii Rydb. -- not accepted
  Pyrola grandiflora var. gormanii Rydb. -- not accepted
  Pyrrocoma clementis Rydb. -- accepted -- tranquil goldenweed
  Pyrrocoma clementis var. clementis Rydb. -- accepted -- tranquil goldenweed
  Pyrrocoma clementis var. villosa (Rydb.) Mayes ex G. Brown & Keil -- accepted -- tranquil goldenweed
  Pyrrocoma villosa Rydb. -- not accepted
  Quamoclidion laevis (Benth.) Rydb. -- not accepted
  Quercus eastwoodiae Rydb. -- not accepted
  Quercus gunnisonii (Torr. & A. Gray) Rydb. -- not accepted
  Quercus harvardii Rydb. -- not accepted -- Harvard oak
  Quercus harvardii var. harvardii Rydb. -- not accepted
  Quercus havardii Rydb. -- accepted -- Havard's oak, Havard's shinnery oak, sand shinnery oak, sand shinoak
  Quercus havardii var. havardii Rydb. -- not accepted -- Havard oak
  Quercus leptophylla Rydb. -- not accepted
  Quercus mandanensis Rydb. -- not accepted
  Quercus mohriana Buckley ex Rydb. -- accepted -- Mohr's oak, Mohr's shinoak
  Quercus nitescens Rydb. -- not accepted
  Quercus novomexicana (A. DC.) Rydb. -- not accepted
  Quercus submollis Rydb. -- not accepted
  Quercus utahensis (A. DC.) Rydb. -- not accepted
  Quercus vreelandii Rydb. -- not accepted
  Quercus wilcoxii Rydb. -- not accepted
  Quercus X pauciloba Rydb. (pro sp.) -- not accepted -- wavyleaf oak
  Raillardella minima Rydb. -- not accepted
  Raillardiopsis Rydb. -- not accepted -- raillardiopsis
  Raillardiopsis muirii (A. Gray) Rydb. -- not accepted -- Muir's raillardiopsis
  Raillardiopsis scabrida (Eastw.) Rydb. -- not accepted -- leafy raillardiopsis
  Ramischia elatior (Lange) Rydb. -- not accepted
  Ranunculus acriformis var. montanensis (Rydb.) L.D. Benson -- accepted -- mountain sharp buttercup
  Ranunculus raninculinus (Nutt.) Rydb. -- not accepted
  Ranunculus ranunculinus (Nutt.) Rydb. -- accepted -- tadpole buttercup
  Ranunculus siciformis Mack. & Bush ex Rydb. -- not accepted
  Rayjacksonia annua (Rydb.) R.L. Hartm. & M.A. Lane -- accepted -- viscid tansyaster
  Rhus radicans var. rydbergii (Small ex Rydb.) Rehder -- not accepted
  Rhytidomene lupinellus (Michx.) Rydb. -- not accepted
  Ribes divaricatum var. inerme (Rydb.) McMinn -- not accepted
  Ribes huronense Rydb. -- not accepted
  Ribes inerme Rydb. -- accepted -- whitestem gooseberries, whitestem gooseberry
  Ribes inerme var. inerme Rydb. -- accepted -- whitestem gooseberry
  Ribes valicola Greene ex Rydb. -- not accepted
  Robinia breviloba Rydb. -- not accepted
  Robinia luxurians (Dieck) Rydb. -- not accepted
  Robinia neomexicana var. subvelutina (Rydb.) Kearney & Peebles -- not accepted
  Rorippa alpina (S. Watson) Rydb. -- accepted -- alpine yellowcress
  Rorippa calycina (Engelm.) Rydb. -- accepted -- persistent sepal yellowcress, persistent-sepal yellowcress
  Rorippa curvipes var. integra (Rydb.) Stuckey -- not accepted
  Rorippa obtusa var. integra (Rydb.) Vict. -- not accepted
  Rorippa palustris var. clavata (Rydb.) Stuckey -- not accepted
  Rorippa palustris var. hispida (Desv.) Rydb. -- not accepted
  Rosa arizonica Rydb. -- not accepted
  Rosa arizonica var. granulifera (Rydb.) Kearney & Peebles -- not accepted
  Rosa aucuparia Rydb. -- not accepted
  Rosa bushii Rydb. -- not accepted
  Rosa butleri Rydb. -- not accepted
  Rosa carolina ssp. subserrulata (Rydb.) W.H. Lewis -- accepted
  Rosa collaris Rydb. -- not accepted
  Rosa conjuncta Rydb. -- not accepted
  Rosa floridana Rydb. -- not accepted
  Rosa granulifera Rydb. -- not accepted
  Rosa nanella Rydb. -- not accepted
  Rosa obtusiuscula Rydb. -- not accepted -- Appalachian Valley rose
  Rosa oreophila Rydb. -- not accepted
  Rosa palmeri Rydb. -- not accepted
  Rosa petiolata Rydb. -- not accepted
  Rosa puberulenta Rydb. -- not accepted
  Rosa standleyi Rydb. -- not accepted
  Rosa subblanda Rydb. -- not accepted
  Rosa subglauca Rydb. -- not accepted
  Rosa subserrulata Rydb. -- not accepted
  Rosa texarkana Rydb. -- not accepted
  Rosa treleasei Rydb. -- not accepted
  Rosa underwoodii Rydb. -- not accepted
  Rosa virginiana var. lamprophylla (Rydb.) Fernald -- not accepted -- Virginia rose
  Rosa woodsii ssp. arizonica (Rydb.) W.H. Lewis & Ertter -- accepted -- Woods' Arizona rose
  Rosa woodsii var. arizonica (Rydb.) W.C. Martin & C.R. Hutchins -- not accepted
  Rosa woodsii var. fendleri (Crép.) Rydb. -- not accepted -- Fendler rose
  Rosa woodsii var. granulifera (Rydb.) W.C. Martin & C.R. Hutchins -- not accepted
  Rosa X collaris Rydb. (pro sp.) -- accepted
  Rosa X palustriformis (Rydb.) Voss -- accepted -- rose
  Rubacer Rydb. -- not accepted
  Rubacer columbianum (Millsp.) Rydb. -- not accepted
  Rubacer odoratum (L.) Rydb. -- not accepted
  Rubacer odoratus (L.) Rydb. -- not accepted
  Rubacer parviflorum (Nutt.) Rydb. -- not accepted
  Rubacer parviflorus (Nutt.) Rydb. -- not accepted
  Rubacer tomentosum Rydb. -- not accepted
  Rubus aboriginum Rydb. -- not accepted -- garden dewberry
  Rubus acalyphaceus (Greene) Rydb. -- not accepted
  Rubus arizonicus (Greene) Rydb. -- not accepted
  Rubus brainerdii Rydb. -- not accepted
  Rubus carolinianus Rydb. -- not accepted
  Rubus carpinifolius Rydb. -- not accepted
  Rubus columbianus (Millsp.) Rydb. -- not accepted
  Rubus eastwoodianus Rydb. -- not accepted
  Rubus franciscanus Rydb. -- not accepted
  Rubus lucidus Rydb. -- not accepted -- manatee dewberry, shiny dewberry
  Rubus melanotrachys (Focke) Rydb. -- not accepted
  Rubus nigerrimus (Greene) Rydb. -- not accepted -- dark raspberry
  Rubus nigricans Rydb. -- not accepted
  Rubus ostryifolius Rydb. -- not accepted -- highbush blackberry
  Rubus peramoenus (Greene) Rydb. -- not accepted
  Rubus persistens Rydb. -- not accepted -- persistent blackberry
  Rubus randii (L.H. Bailey) Rydb. -- not accepted
  Rubus rhodophyllus Rydb. -- not accepted
  Rubus roribaccus (L.H. Bailey) Rydb. -- not accepted -- Lucretia dewberry
  Rubus rubrisetus Rydb. -- not accepted
  Rubus spectabilis var. franciscanus (Rydb.) J.T. Howell -- not accepted -- salmonberry
  Rubus subarcticus (Greene) Rydb. -- not accepted
  Rubus subuniflorus Rydb. -- not accepted
  Rubus ursinus var. eastwoodianus (Rydb.) J.T. Howell -- not accepted
  Rubus viburnifolius (Greene) Rydb. -- not accepted
  Rubus vitifolius var. eastwoodianus (Rydb.) Munz -- not accepted -- Pacific dewberry
  Rubus X ostryifolius Rydb. (pro sp.) -- accepted -- highbush blackberry
  Rumex praecox Rydb. -- accepted -- early dock
  Rupertia hallii (Rydb.) J.W. Grimes -- accepted -- Hall's California tea
  Ruppia pectinata Rydb. -- not accepted
  Rydbergia brandegeei (Porter ex A. Gray) Rydb. -- not accepted
  Sabina horizontalis (Moench) Rydb. -- not accepted
  Sabina monosperma (Engelm.) Rydb. -- not accepted
  Sabina scopulorum (Sarg.) Rydb. -- not accepted
  Sabina utahensis (Engelm.) Rydb. -- not accepted
  Salix acutidens Rydb. -- not accepted
  Salix alaxensis ssp. longistylis (Rydb.) Hultén -- not accepted
  Salix alaxensis var. longistylis (Rydb.) C.K. Schneid. -- accepted -- feltleaf willow
  Salix arctica var. petrophila (Rydb.) Kelso -- not accepted
  Salix atra Rydb. -- not accepted
  Salix barclayi var. padophylla (Rydb.) Kelso -- not accepted
  Salix bebbiana var. perrostrata (Rydb.) C.K. Schneid. -- not accepted
  Salix brachycarpa ssp. niphoclada (Rydb.) Argus -- not accepted -- barrenground willow
  Salix cordifolia var. macounii (Rydb.) C.K. Schneid. -- not accepted
  Salix cyclophylla Rydb. -- not accepted
  Salix dodgeana Rydb. -- not accepted
  Salix exigua var. luteosericea (Rydb.) C.K. Schneid. -- not accepted
  Salix exigua var. stenophylla (Rydb.) C.K. Schneid. -- not accepted
  Salix flava Rydb. -- not accepted
  Salix glauca var. macounii (Rydb.) B. Boivin -- not accepted
  Salix glauca var. niphoclada (Rydb.) Wiggins -- not accepted
  Salix glauca var. seemanii (Rydb.) Ostenf. -- not accepted
  Salix idahoensis (C.R. Ball) Rydb. -- not accepted
  Salix interior var. luteosericea (Rydb.) C.K. Schneid. -- not accepted
  Salix labradorica Rydb. -- not accepted
  Salix lasiolepis var. sandbergii (Rydb.) C.R. Ball -- not accepted
  Salix linearifolia Rydb. -- not accepted
  Salix longistylis Rydb. -- not accepted
  Salix luteosericea Rydb. -- not accepted
  Salix macounii Rydb. -- not accepted
  Salix niphoclada Rydb. -- accepted -- barrenground willow
  Salix nivalis var. saximontana (Rydb.) C.K. Schneid. -- not accepted
  Salix nudescens Rydb. -- not accepted
  Salix ovalifolia var. cyclophylla (Rydb.) C.R. Ball -- accepted -- oval-leaf willow
  Salix pachnophora Rydb. -- not accepted
  Salix padifolia Rydb. -- not accepted
  Salix padophylla Rydb. -- not accepted
  Salix paleoneura Rydb. -- not accepted
  Salix perrostrata Rydb. -- not accepted
  Salix petrophila Rydb. -- accepted -- alpine willow
  Salix pseudocordata (Andersson) Rydb. -- not accepted
  Salix pseudocordata auct. non (Andersson) Rydb. -- not accepted
  Salix pseudomonticola var. padophylla (Rydb.) C.R. Ball -- not accepted
  Salix reticulata var. saximontana (Rydb.) Kelso -- not accepted
  Salix rostrata var. perrostrata (Rydb.) Fernald -- not accepted
  Salix rotundata Rydb. ex Macoun -- not accepted
  Salix rotundifolia ssp. dodgeana (Rydb.) Argus -- not accepted -- timberline willow
  Salix rotundifolia var. dodgeana (Rydb.) A.E. Murray -- accepted -- timberline willow
  Salix sandbergii Rydb. -- not accepted
  Salix saximontana Rydb. -- not accepted
  Salix seemanii Rydb. -- not accepted
  Salix sericea var. subsericea (Andersson) Rydb. -- not accepted
  Salix squamata Rydb. -- not accepted
  Salix stenophylla Rydb. -- not accepted
  Salix stricta (Andersson) Rydb. -- not accepted
  Salix vacciniformis Rydb. -- not accepted
  Salix waghornei Rydb. -- not accepted
  Salix watsonii (Bebb) Rydb. -- not accepted
  Salix wheeleri (Rowlee) Rydb. -- not accepted
  Salix wyomingensis Rydb. -- not accepted
  Salix X waghornei Rydb. (pro sp.) -- accepted -- Waghorn's willow
  Salix X wyomingensis Rydb. (pro sp.) -- accepted
  Salvia carnosa ssp. argentea (Rydb.) Epling -- not accepted
  Salvia carnosa var. argentea (Rydb.) McMinn -- not accepted
  Salvia dorrii ssp. argentea (Rydb.) Munz -- not accepted
  Sambucus microbotrys Rydb. -- not accepted
  Sambucus racemosa ssp. pubens var. microbotrys (Rydb.) Kearney & Peebles -- not accepted
  Sambucus racemosa var. microbotrys (Rydb.) Kearney & Peebles -- accepted -- European red elderberry
  Sanguisorba menziesii Rydb. -- accepted -- Menzies' burnet
  Sartwellia puberula Rydb. -- not accepted
  Saussurea densa (Hook.) Rydb. -- not accepted -- clustered sawwort
  Saxifraga hieraciifolia var. rydbergii (Small ex Rydb.) Engl. & Irmsch. -- not accepted
  Saxifraga rydbergii Small ex Rydb. -- not accepted
  Schkuhria pinnata var. guatemalensis (Rydb.) McVaugh -- not accepted
  Scrophularia occidentalis (Rydb.) E.P. Bicknell -- not accepted
  Scutellaria veronicifolia Rydb. -- not accepted
  Sedum rosea var. frigidum (Rydb.) Hultén -- not accepted
  Sedum roseum var. frigidum (Rydb.) Hultén -- not accepted
  Selaginella densa Rydb. -- accepted -- dense clubmoss, lesser spikemoss, small clubmoss
  Selaginella densa var. densa Rydb. -- not accepted -- dense spikemoss, lesser spikemoss
  Senecio acutidens Rydb. -- not accepted
  Senecio ambrosioides Rydb. -- not accepted
  Senecio crocatus Rydb. -- not accepted -- saffron ragwort
  Senecio eremophilus ssp. kingii (Rydb.) G.W. Douglas & G. Ruyle-Douglas -- not accepted
  Senecio eremophilus var. kingii (Rydb.) Greenm. -- accepted -- King's groundsel, King's ragwort, ragwort groundsel
  Senecio fedifolius Rydb. -- not accepted
  Senecio foetidus var. hydrophiloides (Rydb.) T.M. Barkley ex Cronquist -- not accepted
  Senecio fulgens Rydb. -- not accepted
  Senecio glaucifolius Rydb. -- not accepted
  Senecio greggii Rydb. -- not accepted
  Senecio harbourii Rydb. -- not accepted
  Senecio heterodoxus Greene ex Rydb. -- not accepted
  Senecio hydrophiloides Rydb. -- accepted -- tall groundsel
  Senecio integerrimus var. scribneri (Rydb.) T.M. Barkley -- accepted -- Scribner's ragwort
  Senecio jonesii Rydb. -- not accepted
  Senecio kingii Rydb. -- not accepted
  Senecio leonardii Rydb. -- not accepted
  Senecio longipetiolatus Rydb. -- not accepted
  Senecio millelobatus Rydb. -- not accepted -- Uinta ragwort
  Senecio multicapitatus Greenm. ex Rydb. -- not accepted
  Senecio oodes Rydb. -- not accepted
  Senecio pereziifolius Rydb. -- not accepted
  Senecio platylobus Rydb. -- not accepted
  Senecio pseudaureus Rydb. -- not accepted -- falsegold groundsel
  Senecio pseudaureus var. pseudaureus Rydb. -- not accepted -- falsegold groundsel
  Senecio sanguisorboides Rydb. -- not accepted -- burnet ragwort
  Senecio scribneri Rydb. -- not accepted
  Senecio spartioides var. multicapitatus (Greenm. ex Rydb.) S.L. Welsh -- not accepted -- broom-like ragwort, many-head ragwort, ragwort groundsel
  Senecio streptanthifolius var. oodes (Rydb.) J.F. Bain -- not accepted -- Rocky Mountain groundsel
  Senecio subcuneatus Rydb. -- not accepted
  Senecio tridenticulatus Rydb. -- not accepted -- threetooth ragwort
  Senecio tweedyi Rydb. -- not accepted
  Sericotheca discolor (Pursh) Rydb. -- not accepted
  Sericotheca franciscana Rydb. -- not accepted
  Sericotheca obovata Rydb. -- not accepted
  Sericotheca pachydisca Rydb. -- not accepted
  Sericotheca schaffneri Rydb. -- not accepted
  Seriphidium tridentatum ssp. vaseyanum (Rydb.) W.A. Weber -- not accepted
  Seriphidium tripartitum (Rydb.) W.A. Weber -- not accepted
  Seriphidium vaseyanum (Rydb.) W.A. Weber -- not accepted
  Sesban bispinosus (Jacq.) Rydb. -- not accepted
  Sesban exaltatus (Raf.) Rydb. -- not accepted
  Sesbania drummondii (Rydb.) Cory -- accepted -- poisonbean
  Sesbania exaltata (Raf.) Rydb. ex A.W. Hill -- not accepted -- bigpod sesbania, hemp sesbania
  Sibbaldiopsis Rydb. -- accepted
  Sibbaldiopsis tridentata (Aiton) Rydb. -- accepted -- shrubby fivefingers, shrubby-fivefingers
  Sida sagittifolia (A. Gray) Rydb. -- not accepted
  Sideranthus annuus Rydb. -- not accepted
  Sideranthus australis (Greene) Rydb. -- not accepted
  Sideranthus glaberrimus Rydb. -- not accepted
  Sideranthus puberulus Rydb. -- not accepted
  Sideranthus spinulosus (Pursh) Sweet ex Rydb. -- not accepted
  Sideranthus spinulosus var. glaberrimus (Rydb.) A. Nelson -- not accepted
  Sideranthus turbinellus Rydb. -- not accepted
  Sidopsis hispida (Pursh) Rydb. -- not accepted
  Sieversia campanulata (Greene) Rydb. -- not accepted
  Sieversia canescens (Greene) Rydb. -- not accepted
  Sieversia peckii (Pursh) Rydb. -- not accepted
  Silene antirrhina var. depauperata Rydb. -- not accepted
  Silene antirrhina var. vaccarifolia Rydb. -- not accepted
  Silene drummondii ssp. striata (Rydb.) J.K. Morton -- accepted -- Drummond's campion
  Silene drummondii var. striata (Rydb.) Bocquet -- not accepted -- Drummond's campion
  Sisymbrium viscosum (Rydb.) Blank. -- not accepted
  Smelowskia americana Rydb. -- accepted -- American false candytuft
  Solanum agrimoniifolium Rydb. -- accepted
  Solanum canense Rydb. -- accepted
  Solanum ehrenbergii (Bitter) Rydb. -- accepted
  Solanum interius Rydb. -- accepted -- deadly nightshade
  Solanum subvelutinum Rydb. -- accepted
  Solanum X michoacanum (Bitter) Rydb. -- accepted
  Solanum X sambucinum Rydb. -- accepted
  Solidago altissima ssp. gilvocanescens (Rydb.) Semple -- accepted -- Great Plains late goldendrod, shorthair goldenrod
  Solidago altissima var. gilvocanescens (Rydb.) Semple -- not accepted
  Solidago canadensis var. gilvocanescens Rydb. -- not accepted -- Canadian goldenrod, shorthair goldenrod
  Solidago canescens (Rydb.) Friesner -- not accepted
  Solidago decumbens var. oreophila (Rydb.) Fernald -- not accepted
  Solidago gilvocanescens (Rydb.) Smyth -- not accepted
  Solidago lunellii Rydb. -- not accepted
  Solidago oreophila Rydb. -- not accepted
  Solidago pallida (Porter) Rydb. -- not accepted
  Sophia brachycarpa (Richardson) Rydb. -- not accepted
  Sophia intermedia Rydb. -- not accepted
  Sophia millefolia Rydb. -- not accepted
  Sophia nelsonii Rydb. -- not accepted
  Sophia richardsonii (O.E. Schulz) Rydb. -- not accepted
  Sophia viscosa Rydb. -- not accepted
  Sorbus angustifolia Rydb. -- not accepted
  Sparganium acaule (Beeby ex Macoun) Rydb. -- not accepted
  Sparganium chlorocarpum Rydb. -- not accepted
  Sparganium multipedunculatum (Morong) Rydb. -- not accepted
  Sphaeralcea coccinea (Nutt.) Rydb. -- accepted -- copper mallow, orange globemallow, red falsemallow, scarlet globemallow
  Sphaeralcea coccinea ssp. coccinea (Nutt.) Rydb. -- accepted -- globemallow, scarlet globe-mallow, scarlet globemallow
  Sphaeralcea digitata (Greene) Rydb. -- accepted -- juniper globemallow, slippery globemallow
  Sphaeralcea digitata ssp. digitata (Greene) Rydb. -- accepted -- juniper globemallow
  Sphaeralcea grossulariifolia (Hook. & Arn.) Rydb. -- accepted -- currant-leaf globe-mallow, gooseberryleaf globemallow
  Sphaeralcea grossulariifolia ssp. grossulariifolia (Hook. & Arn.) Rydb. -- accepted -- berryleaf globemallow, gooseberryleaf globemallow
  Sphaeralcea leptophylla (A. Gray) Rydb. -- accepted -- scaly globemallow
  Sphaeralcea munroana ssp. subrhomboidea (Rydb.) Kearney -- accepted -- whitestem globemallow
  Sphaeralcea munroana var. subrhomboidea (Rydb.) Kearney -- not accepted
  Sphaeromeria diversifolia (D.C. Eaton) Rydb. -- accepted -- separateleaf chickensage
  Sphenopholis intermedia (Rydb.) Rydb. -- accepted -- slender wedgegrass, slender wedgescale
  Sphenopholis obtusata f. purpurascens (Vasey ex Rydb. & Shear) Waterf. -- not accepted
  Spiraea douglasii var. roseata (Rydb.) C.L. Hitchc. -- not accepted
  Spiraea stevenii (C.K. Schneid.) Rydb. -- accepted -- beauverd spirea
  Spiraea subvillosa Rydb. -- not accepted
  Spiraea tomentulosa Rydb. -- not accepted
  Spiraea X subcanescens Rydb. (pro sp.) -- accepted -- spirea
  Spiranthes cernua var. ochroleuca (Rydb.) Ames -- not accepted
  Spiranthes ochroleuca (Rydb.) Rydb. -- accepted -- yellow nodding ladies'-tresses, yellow nodding lady's tresses
  Spiranthes stricta (Rydb.) A. Nelson -- not accepted
  Sporobolus aristatus Rydb. -- not accepted
  Sporobolus filiformis (Thurb. ex S. Watson) Rydb. -- not accepted
  Sporobolus flexuosus (Thurb. ex Vasey) Rydb. -- accepted -- mesa dropseed
  Spraguea monosperma (Greene) Rydb. -- not accepted
  Stachys asperrima Rydb. -- not accepted
  Stachys borealis Rydb. -- not accepted
  Stachys homotricha (Fernald) Rydb. -- not accepted
  Stachys subcordata Rydb. -- not accepted
  Stachys teucriifolia Rydb. -- not accepted
  Stachys teucriiformis Rydb. -- not accepted
  Stanleya tomentosa var. runcinata (Rydb.) Rollins -- not accepted -- woolly princesplume
  Stanleyella wrightii (A. Gray) Rydb. -- not accepted
  Stellaria palmeri (Rydb.) Tidestr. -- not accepted
  Stellariopsis santolinoides (A. Gray) Rydb. -- not accepted
  Stenanthella occidentalis (A. Gray) Rydb. -- not accepted
  Stenotopsis interior (Coville) Rydb. -- not accepted
  Stenotopsis linearifolia (DC.) Rydb. -- not accepted
  Stenotus andersonii Rydb. -- not accepted
  Stenotus borealis Rydb. -- accepted -- northern mock goldenweed
  Stenotus lanuginosus var. andersonii (Rydb.) H.M. Hall -- accepted -- Anderson's goldenweed, Anderson's mock goldenweed
  Stipa porteri Rydb. -- not accepted
  Streptanthella Rydb. -- accepted
  Streptanthella longirostris (S. Watson) Rydb. -- accepted -- longbeak fiddle mustard, longbeak streptanthella
  Strobus monticola (Douglas ex D. Don) Rydb. -- not accepted
  Suckleya suckleyana (Torr.) Rydb. -- accepted -- poison suckleya
  Suckleyi suckleyana (Torr.) Rydb. -- not accepted
  Swida foemina (Mill.) Rydb. -- not accepted
  Swida instolonea (A. Nelson) Rydb. -- not accepted
  Swida stolonifera (Michx.) Rydb. -- not accepted
  Symphoricarpos oreophilus var. parishii (Rydb.) Cronquist -- not accepted
  Symphoricarpos oreophilus var. utahensis (Rydb.) A. Nelson -- accepted -- Utah snowberry
  Symphoricarpos parishii Rydb. -- not accepted
  Symphoricarpos rotundifolius var. parishii (Rydb.) Dempster -- accepted -- Parish's snowberry
  Symphoricarpos utahensis Rydb. -- not accepted
  Symphoricarpos vaccinioides Rydb. -- not accepted
  Symphyotrichum ciliolatum var. maccallae (Rydb.) G.L. Nesom -- not accepted
  Symphyotrichum ciliolatum var. wilsonii (Rydb.) G.L. Nesom -- not accepted
  Symphyotrichum falcatum var. crassulum (Rydb.) G.L. Nesom -- not accepted -- white prairie aster
  Symphyotrichum molle (Rydb.) G.L. Nesom -- accepted -- soft aster
  Symphyotrichum X batesii (Rydb.) G.L. Nesom -- accepted
  Symphyotrichum X finkii (Rydb.) G.L. Nesom (pro sp.) -- accepted
  Symphyotrichum X woldenii (Rydb.) G.L. Nesom -- accepted
  Syntherisma humifusum (Pers.) Rydb. -- not accepted
  Synthyris dissecta Rydb. -- accepted -- cut-leaf kittentails
  Synthyris laciniata (A. Gray) Rydb. -- accepted -- western kittentails
  Synthyris laciniata ssp. laciniata (A. Gray) Rydb. -- not accepted -- western kittenstails
  Tagetes alamensis Rydb. -- not accepted
  Taraxacum alaskanum Rydb. -- accepted
  Taraxacum eriophorum Rydb. -- not accepted -- woolbearing dandelion
  Taraxacum ovinum Rydb. -- not accepted
  Taraxacum scopulorum (A. Gray) Rydb. -- accepted -- harp dandelion
  Taraxia subacaulis (Pursh) Rydb. -- accepted -- diffuseflower evening primrose
  Telesonix heucheriformis (Rydb.) Rydb. -- accepted -- alumroot brookfoam
  Telesonix jamesii var. heucheriformis (Rydb.) Bacig. -- not accepted
  Tephrosia angustissima var. curtissii (Small ex Rydb.) Isely -- not accepted -- Curtiss' hoarypea
  Tephrosia carpenteri (Rydb.) Killip -- not accepted
  Tephrosia curtissii (Small ex Rydb.) Shinners -- accepted -- Curtiss' hoarypea
  Tephrosia mohrii (Rydb.) R.K. Godfrey -- accepted -- pineland hoary-pea
  Tephrosia texana (Rydb.) Cory -- not accepted
  Tephrosia thurberi (Rydb.) C.E. Wood -- accepted -- Thurber's hoary-pea, Thurber's hoarypea
  Tesseranthium angustifolium (Rydb.) Rydb. -- not accepted
  Tesseranthium macrophyllum (Greene) Rydb. -- not accepted
  Tetradymia canescens var. inermis (Rydb.) Payson -- not accepted
  Tetraneuris stenophylla Rydb. -- not accepted
  Thalesia lutea (Parry) Rydb. -- not accepted
  Thalictrum confine var. columbianum (Rydb.) B. Boivin -- not accepted
  Thalictrum dasycarpum var. hypoglaucum (Rydb.) B. Boivin -- not accepted
  Thalictrum hypoglaucum Rydb. -- not accepted
  Thalictrum occidentale var. columbianum (Rydb.) M. Peck -- not accepted
  Thelesperma filifolium var. intermedium (Rydb.) Shinners -- not accepted -- stiff greenthread
  Thelesperma intermedium Rydb. -- not accepted
  Thelesperma marginatum Rydb. -- not accepted
  Thelesperma subnudum var. marginatum (Rydb.) T.E. Melchert ex Cronquist -- not accepted -- greenthread, Navajo tea, Navajo-tea
  Thelypodiopsis Rydb. -- accepted -- tumble-mustard, tumblemustard
  Thelypodiopsis aurea (Eastw.) Rydb. -- accepted -- Durango tumblemustard
  Thelypodiopsis elegans (M.E. Jones) Rydb. -- accepted -- Westwater tumble-mustard, Westwater tumblemustard
  Thelypodiopsis juniperorum (Payson) Rydb. -- accepted -- juniper tumblemustard
  Thelypodiopsis sagittata var. ovalifolium (Rydb.) S.L. Welsh -- not accepted
  Thelypodium lasiophyllum var. utahense (Rydb.) Jeps. -- not accepted
  Thelypodium sagittatum ssp. ovalifolium (Rydb.) Al-Shehbaz -- accepted -- arrow thelypody, arrowleaf thelypody
  Thelypodium sagittatum var. ovalifolium (Rydb.) S.L. Welsh & Reveal -- not accepted
  Thelypodium utahense Rydb. -- not accepted
  Thermopsis ovata (B.L. Rob. ex Piper) Rydb. -- not accepted
  Therofon turbinatum Rydb. -- not accepted
  Thlaspi fendleri var. coloradense (Rydb.) Maguire -- not accepted
  Thymophylla pentachaeta var. puberula (Rydb.) Strother -- accepted -- fiveneedle pricklyleaf
  Tiarella californica (Kellogg) Rydb. -- not accepted
  Tiquiliopsis palmeri (A. Gray) Rydb. -- not accepted
  Tithymalus arkansanus var. coloradensis (Norton) Rydb. -- not accepted
  Tium drummondii (Douglas ex Hook.) Rydb. -- not accepted
  Tium michauxii (Kuntze) Rydb. -- not accepted
  Tofieldia glutinosa var. intermedia (Rydb.) B. Boivin -- not accepted
  Townsendia intermedia Rydb. -- not accepted
  Townsendia vreelandii Rydb. -- not accepted
  Toxicodendron radicans var. rydbergii (Small ex Rydb.) Erskine -- not accepted
  Toxicodendron rydbergii (Small ex Rydb.) Greene -- accepted -- poison ivy, western poison ivy
  Toxicoscordion Rydb. -- accepted -- deathcamas
  Toxicoscordion fremontii (Torr.) Rydb. -- accepted -- Fremont's deathcamas
  Toxicoscordion gramineum (Rydb.) Rydb. -- not accepted
  Toxicoscordion nuttallii (A. Gray) Rydb. -- accepted -- Nuttall's deathcamas
  Toxicoscordion paniculatum (Nutt.) Rydb. -- accepted -- foothill deathcamas
  Toxicoscordion venenosum (S. Watson) Rydb. -- accepted -- meadow deathcamas
  Toxicoscordion venenosum var. gramineum (Rydb.) Brasher -- accepted -- grassy deathcamas
  Toxicoscordion venenosum var. venenosum (S. Watson) Rydb. -- accepted -- meadow deathcamas
  Trifolium aitonii Rydb. -- not accepted
  Trifolium bracteolatum Rydb. -- not accepted
  Trifolium dasyphyllum ssp. uintense (Rydb.) J.M. Gillett -- accepted -- Uinta clover
  Trifolium dasyphyllum var. stenolobum (Rydb.) McDermott -- not accepted
  Trifolium dasyphyllum var. uintense (Rydb.) J.S. Martin ex Isely -- not accepted
  Trifolium dasyphyllum var. uintense (Rydb.) S.L. Welsh -- not accepted
  Trifolium inaequale Rydb. -- not accepted
  Trifolium lilacinum Rydb. -- not accepted
  Trifolium lividum Rydb. -- not accepted
  Trifolium longipes ssp. pedunculatum (Rydb.) J.M. Gillett -- accepted -- longstalk clover
  Trifolium longipes var. pedunculatum (Rydb.) C.L. Hitchc. -- not accepted
  Trifolium longipes var. pedunculatum (Rydb.) Isely -- not accepted
  Trifolium montanense Rydb. -- not accepted
  Trifolium oxydon Greene ex Rydb. -- not accepted
  Trifolium oxyodon Greene ex Rydb. -- not accepted
  Trifolium parryi ssp. montanense (Rydb.) J.M. Gillett -- accepted -- Parry's clover
  Trifolium parryi ssp. salictorum (Greene ex Rydb.) J.M. Gillett -- accepted -- Parry's clover
  Trifolium parryi var. montanense (Rydb.) Isely -- not accepted
  Trifolium parryi var. montanense (Rydb.) S.L. Welsh -- not accepted
  Trifolium pedunculatum Rydb. -- not accepted
  Trifolium salictorum Greene ex Rydb. -- not accepted
  Trifolium stenolobum Rydb. -- not accepted
  Trifolium uintense Rydb. -- not accepted
  Triosteum illinoense (Wiegand) Rydb. -- not accepted
  Triphora trianthophora (Sw.) Rydb. -- not accepted -- three birds orchid, threebirds
  Triphora trianthophora var. trianthophora (Sw.) Rydb. -- not accepted -- threebirds
  Triphora trianthophoros (Sw.) Rydb. -- accepted -- three birds orchid, threebirds
  Triphora trianthophoros var. trianthophoros (Sw.) Rydb. -- accepted -- threebirds
  Trisetum majus Vasey ex Rydb. -- not accepted
  Trisetum spicatum ssp. majus (Vasey ex Rydb.) Hultén -- not accepted
  Trisetum spicatum var. majus (Rydb.) Farw. -- not accepted
  Trollius albiflorus (A. Gray) Rydb. -- accepted
  Unamia alba (Nutt.) Rydb. -- not accepted
  Unamia lutescens (Lindl. ex DC.) Rydb. -- not accepted
  Urtica cardiophylla Rydb. -- not accepted
  Urtica strigosissima Rydb. -- not accepted
  Urtica viridis Rydb. -- not accepted
  Vaccinium globulare Rydb. -- not accepted
  Vaccinium myrtillus ssp. oreophilum (Rydb.) A. Löve & D. Löve & Kapoor -- not accepted
  Vaccinium myrtillus var. oreophilum (Rydb.) Dorn -- not accepted -- whortleberry
  Vaccinium oreophilum Rydb. -- not accepted
  Vagnera australis Rydb. -- not accepted
  Vagnera liliacea (Greene) Rydb. -- not accepted
  Valeriana acutiloba Rydb. -- accepted -- cordilleran valerian, sharpleaf valerian
  Valeriana acutiloba var. acutiloba Rydb. -- accepted -- sharpleaf valerian
  Valeriana acutiloba var. ovata (Rydb.) A. Nelson -- not accepted
  Valeriana acutiloba var. pubicarpa (Rydb.) Cronquist -- accepted -- hairyfruit valerian, hairyfruit valeriana
  Valeriana capitata ssp. acutiloba (Rydb.) F.G. Mey. -- not accepted
  Valeriana capitata ssp. pubicarpa (Rydb.) F.G. Mey. -- not accepted
  Valeriana ovata Rydb. -- not accepted
  Valeriana puberulenta Rydb. -- not accepted
  Valeriana pubicarpa Rydb. -- not accepted
  Valeriana scouleri Rydb. -- not accepted -- Scouler's valerian
  Valeriana septentrionalis Rydb. -- not accepted
  Valeriana sitchensis ssp. scouleri (Rydb.) F.G. Mey. -- accepted
  Valeriana sitchensis var. scouleri (Rydb.) M.E. Jones -- not accepted
  Valeriana uliginosa (Torr. & A. Gray) Rydb. -- not accepted -- mountain valerian
  Vanquelinia angustifolia Rydb. -- not accepted
  Vauquelinia angustifolia Rydb. -- not accepted
  Vauquelinia corymbosa ssp. angustifolia (Rydb.) W.J. Hess & Henrickson -- accepted -- slimleaf rosewood
  Veratrum eschscholtzianum (Schult. & Schult. f.) Rydb. ex A. Heller -- not accepted
  Veratrum speciosum Rydb. -- not accepted
  Verbena ambrosiifolia Rydb. ex Small -- not accepted
  Verbena pumila Rydb. -- not accepted
  Vesicarpa Rydb. -- accepted
  Vesicarpa potentilloides (A. Gray) Rydb. -- not accepted
  Vesicarpa potentilloides var. potentilloides (A. Gray) Rydb. -- not accepted
  Vicia producta Rydb. -- not accepted
  Vicia trifida Rydb. -- not accepted
  Viola montanensis Rydb. -- not accepted
  Viola venosa (S. Watson) Rydb. -- not accepted
  Viorna scottii (Porter) Rydb. -- not accepted
  Viorna versicolor (Small ex Rydb.) Small -- not accepted
  Vulpia megalura (Nutt.) Rydb. -- not accepted
  Vulpia octoflora (Walter) Rydb. -- accepted -- eight-flower six-weeks grass, pullout grass, sixweeks fescue, sixweeks grass
  Vulpia octoflora var. octoflora (Walter) Rydb. -- accepted -- eight-flower six-weeks grass, sixweeks fescue
  Vulpia pacifica (Piper) Rydb. -- not accepted
  Vulpia reflexa (Buckley) Rydb. -- not accepted
  Wahlbergella attenuata (Farr) Rydb. -- not accepted
  Wahlbergella drummondii (Hook.) Rydb. -- not accepted
  Wahlbergella kingii (S. Watson) Rydb. -- not accepted
  Wahlbergella montana (S. Watson) Rydb. -- not accepted
  Wahlbergella parryi (S. Watson) Rydb. -- not accepted
  Wahlbergella striata (Rydb.) Rydb. -- not accepted
  Wahlbergella tayloriae (B.L. Rob.) Rydb. -- not accepted
  Xanthisma spinulosum var. glaberrimum (Rydberg) D.R. Morgan & R.L. Hartm. -- accepted
  Xanthoxalis coloradensis (Rydb.) Rydb. -- not accepted
  Ximenesia exauriculata (B.L. Rob. & Greenm.) Rydb. -- not accepted
  Xylophacos argophyllus (Nutt.) Rydb. -- not accepted
  Xylophacos missouriensis (Nutt.) Rydb. -- not accepted
  Xylorhiza coloradoensis (A. Gray) Rydb. -- not accepted
  Xylorhiza lanceolata Rydb. -- not accepted
  Yucca gilbertiana (Trel.) Rydb. -- not accepted
  Zeia smithii (Rydb.) Lunell -- not accepted
  Zigadenus gramineus Rydb. -- not accepted
  Zigadenus intermedius Rydb. -- not accepted
  Zigadenus vaginatus (Rydb.) J.F. Macbr. -- not accepted -- sheathed deathcamas
  Zigadenus venenosus var. gramineus (Rydb.) Walsh ex M. Peck -- not accepted -- deathcamas, grassy deathcamas
  Zizania interior (Fassett) Rydb. -- not accepted
   

A gray bar