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Plant List
Indexed Alphabetically by Common Name
R-S
For a list of plants indexed by Scientific Name, click here
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| National Common Name | Scientific Name with Author | Symbol | Family | |
| Rabbit Valley gilia | Aliciella caespitosa (Gray) J.M. Porter | ALCA23 | Polemoniaceae | |
| rabbitbells | Crotalaria rotundifolia Walt. ex J.F. Gmel. | CRRO5 | Fabaceae | |
| rabbitbrush | Chrysothamnus Nutt. | CHRYS9 | Asteraceae | |
| rabbitear rockcress | Arabis pendulina Greene | ARPE | Brassicaceae | |
| rabbitear rockcress | Arabis pendulina Greene var. pendulina | ARPEP | Brassicaceae | |
| rabbithead balsamroot | Balsamorhiza hookeri (Hook.) Nutt. var. lagocephala (Sharp) Cronq. | BAHOL | Asteraceae | |
| rabo de gato | Arundinella hispida (Humb. & Bonpl. ex Willd.) Kuntze | ARHI10 | Poaceae | |
| rabo de gato | Arundinella Raddi | ARUND3 | Poaceae | |
| rabo de ranton | Casearia aculeata Jacq. | CAAC3 | Flacourtiaceae | |
| raceme pussytoes | Antennaria racemosa Hook. | ANRA | Asteraceae | |
| Radford's sedge | Carex radfordii Gaddy | CARA20 | Cyperaceae | |
| radiate fingergrass | Chloris radiata (L.) Sw. | CHRA | Poaceae | |
| ragged rockflower | Crossosoma bigelovii S. Wats. | CRBI2 | Crossosomataceae | |
| ragged rockflower | Crossosoma bigelovii S. Wats. var. bigelovii | CRBIB | Crossosomataceae | |
| ragged rockflower | Crossosoma bigelovii S. Wats. var. glaucum (Small) Kearney & Peebles | CRBIG | Crossosomataceae | |
| ragleaf | Crassocephalum Moench | CRASS2 | Asteraceae | |
| ragleaf bahia | Bahia dissecta (Gray) Britt. | BADI | Asteraceae | |
| ragweed | Ambrosia L. | AMBRO | Asteraceae | |
| ragweed sagebrush | Artemisia franserioides Greene | ARFR3 | Asteraceae | |
| Raiche's clarkia | Clarkia concinna (Fisch. & C.A. Mey.) Greene ssp. raichei G. Allen, V. Ford & L. Gottlieb | CLCOR | Onagraceae | |
| Raiche's manzanita | Arctostaphylos stanfordiana Parry ssp. raichei W. Knight | ARSTR | Ericaceae | |
| railhead milkvetch | Astragalus terminalis S. Wats. | ASTE9 | Fabaceae | |
| railroadfence | Bauhinia pauletia Pers. | BAPA3 | Fabaceae | |
| Rainbow manzanita | Arctostaphylos rainbowensis J.E. Keeley & A. Massihi | ARRA7 | Ericaceae | |
| rainforest spleenwort | Asplenium normale D. Don | ASNO4 | Aspleniaceae | |
| rainlily | Cooperia Herbert | COOPE | Liliaceae | |
| raintree | Brunfelsia L. | BRUNF2 | Solanaceae | |
| rakkyo | Allium chinense G. Don | ALCH5 | Liliaceae | |
| rambai | Baccaurea motleyana (Muell. Arg.) Muell. Arg. | BAMO4 | Euphorbiaceae | |
| Ramensk's sedge | Carex ramenskii Komarov | CARA4 | Cyperaceae | |
| ramon | Brosimum alicastrum Sw. ssp. alicastrum | BRALA2 | Moraceae | |
| Ramona clarkia | Clarkia similis Lewis & Ernst | CLSI | Onagraceae | |
| Ramona spineflower | Chorizanthe leptotheca Goodman | CHLE6 | Polygonaceae | |
| rampion | Campanula rapunculus L. | CARA19 | Campanulaceae | |
| rampion bellflower | Campanula rapunculoides L. | CARA | Campanulaceae | |
| ram's head lady's slipper | Cypripedium arietinum Ait. f. | CYAR5 | Orchidaceae | |
| Ramshaw Meadows sand verbena | Abronia alpina Brandeg. | ABAL | Nyctaginaceae | |
| rape | Brassica napus L. | BRNA | Brassicaceae | |
| rape | Brassica napus L. var. napus | BRNAN2 | Brassicaceae | |
| rape mustard | Brassica rapa L. ssp. rapa | BRRAR2 | Brassicaceae | |
| Rapp's biatorella lichen | Biatorella rappii Zahlbr. | BIRA3 | Biatorellaceae | |
| Rapp's cup lichen | Cladonia rappii A. Evans | CLRA5 | Cladoniaceae | |
| Rapp's shell lichen | Arthopyrenia rappii Zahlbr. | ARRA6 | Arthopyreniaceae | |
| rare loco milkvetch | Astragalus leptocarpus Torr. & Gray | ASLE10 | Fabaceae | |
| rat's ear | Commelina forskaolii Vahl | COFO3 | Commelinaceae | |
| rat-tail cholla | Cylindropuntia ×viridiflora (Britt. & Rose) F.M. Knuth (pro sp.) [imbricata × whipplei] | CYVI16 | Cactaceae | |
| rat-tail orchid | Bulbophyllum pachyrrachis (A. Rich.) Griseb. | BUPA2 | Orchidaceae | |
| rattan | Calamus rotang L. | CARO32 | Arecaceae | |
| Rattan's cryptantha | Cryptantha rattanii Greene | CRRA3 | Boraginaceae | |
| Rattan's milkvetch | Astragalus rattanii Gray | ASRA4 | Fabaceae | |
| Rattan's milkvetch | Astragalus rattanii Gray var. rattanii | ASRAR3 | Fabaceae | |
| Rattan's sandmat | Chamaesyce ocellata (Dur. & Hilg.) Millsp. ssp. rattanii (S. Wats.) Koutnik | CHOCR | Euphorbiaceae | |
| rattlebox | Crotalaria alata Buch.-Ham. ex D. Don | CRAL12 | Fabaceae | |
| rattlebox | Crotalaria L. | CROTA | Fabaceae | |
| rattlebox | Crotalaria mysorensis Roth | CRMY | Fabaceae | |
| rattlebox | Crotalaria paulina Schrank | CRPA22 | Fabaceae | |
| rattlebox | Crotalaria vitellina Ker Gawler | CRVI13 | Fabaceae | |
| rattlesnake brome | Bromus briziformis Fisch. & C.A. Mey. | BRBR5 | Poaceae | |
| rattlesnake fern | Botrychium virginianum (L.) Sw. | BOVI | Ophioglossaceae | |
| rattlesnake flower | Brazoria truncata (Benth.) Engelm. & Gray | BRTR | Lamiaceae | |
| rattlesnake flower | Brazoria truncata (Benth.) Engelm. & Gray var. truncata | BRTRT2 | Lamiaceae | |
| rattlesnake plant | Calathea crotalifera S. Wats. | CACR19 | Marantaceae | |
| rattleweed | Crotalaria retusa L. | CRRE4 | Fabaceae | |
| Raup's Indian paintbrush | Castilleja raupii Pennell | CARA7 | Scrophulariaceae | |
| Ravenel's bruchia moss | Bruchia ravenelii Wils in Sull. | BRRA5 | Bruchiaceae | |
| Ravenel's cryphaea moss | Cryphaea ravenelii Aust. | CRRA7 | Cryphaeaceae | |
| Ravenel's cup lichen | Cladonia ravenelii Tuck. | CLRA3 | Cladoniaceae | |
| Ravenel's dot lichen | Arthonia ravenelii Tuck. | ARRA5 | Arthoniaceae | |
| Ravenel's dotted lichen | Bacidia ravenelii (Tuck.) Zahlbr. | BARA2 | Bacidiaceae | |
| ravenfoot sedge | Carex crus-corvi Shuttlw. ex Kunze | CACR8 | Cyperaceae | |
| Raven's milkvetch | Astragalus ravenii Barneby | ASRA5 | Fabaceae | |
| ravine cyanea | Cyanea dunbariae Rock | CYDU3 | Campanulaceae | |
| ravine midsorus fern | Blechnum divergens (Kunze) Mett. | BLDI | Blechnaceae | |
| ravine sedge | Carex impressinervia Bryson, Kral & Manhart | CAIM2 | Cyperaceae | |
| Rawhide HIll onion | Allium tuolumnense (Ownbey & Aase) S. Denison & McNeal | ALTU | Liliaceae | |
| ray fern | Actinostachys pennula (Sw.) Hook. | ACPE2 | Schizaeaceae | |
| rayless arnica | Arnica ×diversifolia Greene (pro sp.) [amplexicaulis or mollis × cordifolia or latifolia] | ARDI7 | Asteraceae | |
| rayless arnica | Arnica discoidea Benth. | ARDI6 | Asteraceae | |
| rayless goldenhead | Acamptopappus sphaerocephalus (Harvey & Gray ex Gray) Gray | ACSP | Asteraceae | |
| rayless goldenhead | Acamptopappus sphaerocephalus (Harvey & Gray ex Gray) Gray var. hirtellus Blake | ACSPH | Asteraceae | |
| rayless goldenhead | Acamptopappus sphaerocephalus (Harvey & Gray ex Gray) Gray var. sphaerocephalus | ACSPS2 | Asteraceae | |
| rayless goldenrod | Bigelowia DC. | BIGEL | Asteraceae | |
| Raymond's sedge | Carex raymondii Calder | CARA9 | Cyperaceae | |
| Raynolds' sedge | Carex raynoldsii Dewey | CARA6 | Cyperaceae | |
| recurved brotherella moss | Brotherella recurvans (Michx.) Fleisch. | BRRE3 | Sematophyllaceae | |
| recurved bryoerythrophyllum moss | Bryoerythrophyllum recurvum (Griff.) Saito | BRRE4 | Pottiaceae | |
| recurved milkvetch | Astragalus recurvus Greene | ASRE2 | Fabaceae | |
| red alder | Alnus rubra Bong. | ALRU2 | Betulaceae | |
| red amaranth | Amaranthus cruentus L. | AMCR4 | Amaranthaceae | |
| red baneberry | Actaea rubra (Ait.) Willd. | ACRU2 | Ranunculaceae | |
| red baneberry | Actaea rubra (Ait.) Willd. ssp. arguta (Nutt.) Hultén | ACRUA8 | Ranunculaceae | |
| red baneberry | Actaea rubra (Ait.) Willd. ssp. rubra | ACRUR2 | Ranunculaceae | |
| red beadtree | Adenanthera pavonina L. | ADPA | Fabaceae | |
| red besseya | Besseya rubra (Dougl. ex Hook.) Rydb. | BERU | Scrophulariaceae | |
| red bloodwood | Corymbia gummifera (Soland. ex Gaertn.) K.D. Hill & L.A. Johnson | COGU4 | Myrtaceae | |
| red brome | Bromus rubens L. | BRRU2 | Poaceae | |
| red buckeye | Aesculus pavia L. | AEPA | Hippocastanaceae | |
| red buckeye | Aesculus pavia L. var. flavescens (Sarg.) Correll | AEPAF | Hippocastanaceae | |
| red buckeye | Aesculus pavia L. var. pavia | AEPAP | Hippocastanaceae | |
| red bulrush | Blysmus rufus (Huds.) Link | BLRU | Cyperaceae | |
| red columbine | Aquilegia canadensis L. | AQCA | Ranunculaceae | |
| red cryptocarya | Cryptocarya rubra (Molina) Skeels | CRRU12 | Lauraceae | |
| red cyphomeris | Cyphomeris gypsophiloides (Mart. & Gal.) Standl. | CYGY | Nyctaginaceae | |
| red false beardgrass | Chrysopogon fulvus (Spreng.) Chiov. | CHFU | Poaceae | |
| red floripontio | Brugmansia sanguinea (Ruiz & Pavon) D. Don | BRSA3 | Solanaceae | |
| red fruit bearberry | Arctostaphylos rubra (Rehd. & Wilson) Fern. | ARRU | Ericaceae | |
| red ginger | Alpinia purpurata (Vieill.) K. Schum. | ALPU4 | Zingiberaceae | |
| red goosefoot | Chenopodium rubrum L. | CHRU | Chenopodiaceae | |
| red grama | Bouteloua trifida Thurb. | BOTR2 | Poaceae | |
| red grama | Bouteloua trifida Thurb. var. burkii (Scribn. ex S. Wats.) Vasey ex L.H. Dewey | BOTRB | Poaceae | |
| red grama | Bouteloua trifida Thurb. var. trifida | BOTRT | Poaceae | |
| red hawksbeard | Crepis rubra L. | CRRU9 | Asteraceae | |
| red hawthorn | Crataegus erythrocarpa Ashe | CRER3 | Rosaceae | |
| red hickory | Carya ovalis (Wangenh.) Sarg. | CAOV3 | Juglandaceae | |
| red hills soap plant | Chlorogalum grandiflorum Hoover | CHGR3 | Liliaceae | |
| red horse-chestnut | Aesculus ×carnea Hayne [hippocastanum × pavia] | AECA2 | Hippocastanaceae | |
| red manjack | Cordia collococca L. | COCO5 | Boraginaceae | |
| red maple | Acer rubrum L. | ACRU | Aceraceae | |
| red maple | Acer rubrum L. var. rubrum | ACRUR | Aceraceae | |
| red maple | Acer rubrum L. var. trilobum Torr. & Gray ex K. Koch | ACRUT | Aceraceae | |
| red milkweed | Asclepias rubra L. | ASRU | Asclepiadaceae | |
| red moneywort | Alysicarpus rugosus (Willd.) DC. | ALRU4 | Fabaceae | |
| red powderpuff | Calliandra haematomma (Bertero ex DC.) Benth. | CAHA10 | Fabaceae | |
| red pricklypoppy | Argemone sanguinea Greene | ARSA4 | Papaveraceae | |
| red ribbons | Clarkia concinna (Fisch. & C.A. Mey.) Greene | CLCO | Onagraceae | |
| red ribbons | Clarkia concinna (Fisch. & C.A. Mey.) Greene ssp. automixa R.N. Bowman | CLCOA | Onagraceae | |
| red ribbons | Clarkia concinna (Fisch. & C.A. Mey.) Greene ssp. concinna | CLCOC | Onagraceae | |
| red sand verbena | Abronia maritima Nutt. ex S. Wats. | ABMA2 | Nyctaginaceae | |
| red Sierra onion | Allium obtusum J.G. Lemmon | ALOB | Liliaceae | |
| red Sierra onion | Allium obtusum J.G. Lemmon var. conspicuum Mortola & McNeal | ALOBC | Liliaceae | |
| red Sierra onion | Allium obtusum J.G. Lemmon var. obtusum | ALOBO | Liliaceae | |
| red silk cottontree | Bombax ceiba L. | BOCE2 | Bombacaceae | |
| red spiderling | Boerhavia diffusa L. | BODI3 | Nyctaginaceae | |
| red star-thistle | Centaurea calcitrapa L. | CECA2 | Asteraceae | |
| red triangles | Centrostegia thurberi Gray ex Benth. | CETH3 | Polygonaceae | |
| red turtlehead | Chelone obliqua L. | CHOB3 | Scrophulariaceae | |
| red turtlehead | Chelone obliqua L. var. obliqua | CHOBO | Scrophulariaceae | |
| red turtlehead | Chelone obliqua L. var. speciosa Pennell & Wherry | CHOBS | Scrophulariaceae | |
| red valerian | Centranthus ruber (L.) DC. | CERU2 | Valerianaceae | |
| red wattle | Acacia silvestris Tindale | ACSI5 | Fabaceae | |
| red windflower | Anemone multifida Poir. var. saxicola Boivin | ANMUS | Ranunculaceae | |
| redbud | Cercis L. | CERCI2 | Fabaceae | |
| redclay hawthorn | Crataegus impar Beadle | CRIM6 | Rosaceae | |
| redclay suncup | Camissonia parryi (S. Wats.) Raven | CAPA38 | Onagraceae | |
| redflower gum | Corymbia ficifolia (F. Muell.) K.D. Hill & L.A. Johnson | COFI7 | Myrtaceae | |
| redflower ragleaf | Crassocephalum crepidioides (Benth.) S. Moore | CRCR9 | Asteraceae | |
| red-gland spurge | Chamaesyce melanadenia (Torr.) Millsp. | CHME5 | Euphorbiaceae | |
| redgum | Corymbia calophylla (Lindl.) K.D. Hill & L.A. Johnson | COCA48 | Myrtaceae | |
| red-hair cyrtandra | Cyrtandra ferripilosa St. John | CYFE9 | Gesneriaceae | |
| redheart | Ceanothus spinosus Nutt. | CESP | Rhamnaceae | |
| red-hot cat's tail | Acalypha hispida Burm. f. | ACHI2 | Euphorbiaceae | |
| red-leaf wattle | Acacia rubida A. Cunn. | ACRU11 | Fabaceae | |
| redmaids | Calandrinia Kunth | CALAN | Portulacaceae | |
| redosier dogwood | Cornus sericea L. | COSE16 | Cornaceae | |
| redosier dogwood | Cornus sericea L. ssp. sericea | COSES | Cornaceae | |
| redring milkweed | Asclepias variegata L. | ASVA | Asclepiadaceae | |
| redroot amaranth | Amaranthus retroflexus L. | AMRE | Amaranthaceae | |
| redroot cryptantha | Cryptantha micrantha (Torr.) I.M. Johnston | CRMI | Boraginaceae | |
| redroot cryptantha | Cryptantha micrantha (Torr.) I.M. Johnston var. lepida (Gray) I.M. Johnston | CRMIL2 | Boraginaceae | |
| redroot cryptantha | Cryptantha micrantha (Torr.) I.M. Johnston var. micrantha | CRMIM | Boraginaceae | |
| redroot flatsedge | Cyperus erythrorhizos Muhl. | CYER2 | Cyperaceae | |
| redshank | Adenostoma sparsifolium Torr. | ADSP | Rosaceae | |
| redskin onion | Allium haematochiton S. Wats. | ALHA | Liliaceae | |
| redspot clarkia | Clarkia speciosa H.F. & M.E. Lewis | CLSP | Onagraceae | |
| redspot clarkia | Clarkia speciosa H.F. & M.E. Lewis ssp. nitens (H.F. & M.E. Lewis) Lewis & Raven | CLSPN | Onagraceae | |
| redspot clarkia | Clarkia speciosa H.F. & M.E. Lewis ssp. polyantha H.F. & M.E. Lewis | CLSPP | Onagraceae | |
| redspot clarkia | Clarkia speciosa H.F. & M.E. Lewis ssp. speciosa | CLSPS | Onagraceae | |
| redstem | Ammannia L. | AMMAN | Lythraceae | |
| redstem ceanothus | Ceanothus sanguineus Pursh | CESA | Rhamnaceae | |
| redstem springbeauty | Claytonia rubra (T.J. Howell) Tidestrom | CLRU2 | Portulacaceae | |
| redstem springbeauty | Claytonia rubra (T.J. Howell) Tidestrom ssp. depressa (Gray) J.M. Miller & K. Chambers | CLRUD | Portulacaceae | |
| redstem springbeauty | Claytonia rubra (T.J. Howell) Tidestrom ssp. rubra | CLRUR | Portulacaceae | |
| redstem wormwood | Artemisia scoparia Waldst. & Kit. | ARSC4 | Asteraceae | |
| redtop | Agrostis gigantea Roth | AGGI2 | Poaceae | |
| reedgrass | Calamagrostis Adans. | CALAM | Poaceae | |
| Reed's bryum moss | Bryum reedii Robins. | BRRE5 | Bryaceae | |
| reflected grapefern | Botrychium echo W.H. Wagner | BOEC | Ophioglossaceae | |
| reflexed flatsedge | Cyperus refractus Engelm. ex Boeckl. | CYRE3 | Cyperaceae | |
| reflexed sedge | Carex retroflexa Muhl. ex Willd. | CARE9 | Cyperaceae | |
| Refugio manzanita | Arctostaphylos refugioensis Gankin | ARRE5 | Ericaceae | |
| Regel's chickweed | Cerastium regelii Ostenf. | CERE4 | Caryophyllaceae | |
| reindeer lichen | Cladina (Nyl.) Nyl. | CLADI3 | Cladoniaceae | |
| reindeer lichen | Cladina arbuscula (Wallr.) Hale & Culb. | CLAR60 | Cladoniaceae | |
| reindeer lichen | Cladina mitis (Sandst.) Hustich | CLMI60 | Cladoniaceae | |
| reindeer lichen | Cladina portentosa (Dufour) Follmann | CLPO4 | Cladoniaceae | |
| reindeer lichen | Cladina stygia (Fr.) Ahti | CLST5 | Cladoniaceae | |
| reindeer lichen | Cladina submitis (A. Evans) Hale & Culb. | CLSU6 | Cladoniaceae | |
| reindeer lichen | Cladina subtenuis (Abbayes) Hale & Culb. | CLSU7 | Cladoniaceae | |
| reindeer lichen | Cladina terrae-novae (Ahti) Hale & Culb. | CLTE9 | Cladoniaceae | |
| relaxgrass | Aegopogon cenchroides Humb. & Bonpl. | AECE | Poaceae | |
| relaxgrass | Aegopogon Humb. & Bonpl. ex Willd. | AEGOP2 | Poaceae | |
| Remy's cyanea | Cyanea remyi Rock | CYRE10 | Campanulaceae | |
| Remy's sandmat | Chamaesyce remyi (Gray ex Boiss.) Croizat & Deg. | CHRE3 | Euphorbiaceae | |
| Remy's sandmat | Chamaesyce remyi (Gray ex Boiss.) Croizat & Deg. var. hanaleiensis (Sherff) O.& I. Deg. | CHREH | Euphorbiaceae | |
| Remy's sandmat | Chamaesyce remyi (Gray ex Boiss.) Croizat & Deg. var. kauaiensis (O. Deg. & Sherff) O.& I. Deg. | CHREK | Euphorbiaceae | |
| Remy's sandmat | Chamaesyce remyi (Gray ex Boiss.) Croizat & Deg. var. remyi | CHRER | Euphorbiaceae | |
| Rendle's meadow foxtail | Alopecurus rendlei Eig | ALRE3 | Poaceae | |
| rescuegrass | Bromus catharticus Vahl | BRCA6 | Poaceae | |
| resin birch | Betula glandulosa Michx. | BEGL | Betulaceae | |
| resin birch | Betula neoalaskana Sarg. | BENE4 | Betulaceae | |
| resinleaf brickellbush | Brickellia baccharidea Gray | BRBA2 | Asteraceae | |
| resinous snakeroot | Ageratina resiniflua (Urban) King & H.E. Robins. | AGRE3 | Asteraceae | |
| reticulate cetraria lichen | Cetraria ericetorum Opiz ssp. reticulata (Rasanen) Karnefelt | CEERR | Parmeliaceae | |
| Reverchon's hawthorn | Crataegus reverchonii Sarg. | CRRE3 | Rosaceae | |
| rhinoceros cactus | Coryphantha echinus (Engelm.) Britt. & Rose | COEC | Cactaceae | |
| rhizoma peanut | Arachis glabrata Benth. [excluded] | ARGL18 | Fabaceae | |
| rhizoma peanut | Arachis hagenbeckii Harms | ARHA10 | Fabaceae | |
| Rhodes grass | Chloris gayana Kunth | CHGA2 | Poaceae | |
| ribbed cryptantha | Cryptantha costata Brandeg. | CRCO15 | Boraginaceae | |
| ribbed sedge | Carex virescens Muhl. ex Willd. | CAVI4 | Cyperaceae | |
| ribseed sandmat | Chamaesyce glyptosperma (Engelm.) Small | CHGL13 | Euphorbiaceae | |
| ricefield flatsedge | Cyperus iria L. | CYIR | Cyperaceae | |
| ricegrass | ×Achnella Barkworth | ACHNE | Poaceae | |
| Richardson's bittercress | Cardamine digitata Richards. | CADI9 | Brassicaceae | |
| Richardson's brookfoam | Boykinia richardsonii (Hook.) Rothrock | BORI2 | Saxifragaceae | |
| Richardson's calliergon moss | Calliergon richardsonii (Mitt.) Kindb. in Warnst. | CARI70 | Amblystegiaceae | |
| Richardson's needlegrass | Achnatherum richardsonii (Link) Barkworth | ACRI8 | Poaceae | |
| Richardson's sedge | Carex richardsonii R. Br. | CARI | Cyperaceae | |
| richweed | Collinsonia canadensis L. | COCA4 | Lamiaceae | |
| richwoods sedge | Carex oligocarpa Schkuhr ex Willd. | CAOL2 | Cyperaceae | |
| Riddell's dozedaisy | Aphanostephus riddellii Torr. & Gray | APRI | Asteraceae | |
| ridge beggartick | Bidens gardneri Baker | BIGA | Asteraceae | |
| ridge rollandia | Cyanea longiflora (Wawra) Lammers, Givnish & Systma | CYLO12 | Campanulaceae | |
| ridged goosefoot | Chenopodium carnosulum Moq. | CHCA12 | Chenopodiaceae | |
| ridged goosefoot | Chenopodium carnosulum Moq. var. patagonicum (Phil.) H.A. Wahl | CHCAP | Chenopodiaceae | |
| ridgestem false foxglove | Agalinis oligophylla Pennell | AGOL | Scrophulariaceae | |
| rigid aloina moss | Aloina rigida (Hedw.) Limpr. | ALRI2 | Pottiaceae | |
| rigid Indian paintbrush | Castilleja rigida Eastw. | CARI12 | Scrophulariaceae | |
| rigid sedge | Carex tetanica Schkuhr | CATE6 | Cyperaceae | |
| rimmed lichen | Aspicilia A. Massal. | ASPIC2 | Hymeneliaceae | |
| rimmed lichen | Aspicilia albopruinosa (Looman) | ASAL14 | Hymeneliaceae | |
| rimmed lichen | Aspicilia alboradiata (H. Magn.) Oksner | ASAL15 | Hymeneliaceae | |
| rimmed lichen | Aspicilia annulata (Lynge) J. W. Thomson | ASAN14 | Hymeneliaceae | |
| rimmed lichen | Aspicilia anseris (Lynge) J. W. Thomson | ASAN15 | Hymeneliaceae | |
| rimmed lichen | Aspicilia caesiocinerea (Nyl. ex Malbr.) Arnold | ASCA36 | Hymeneliaceae | |
| rimmed lichen | Aspicilia caesiopruinosa (H. Magn.) J. W. Thomson | ASCA37 | Hymeneliaceae | |
| rimmed lichen | Aspicilia candida (Anzi) Hue | ASCA39 | Hymeneliaceae | |
| rimmed lichen | Aspicilia cinerea (L.) Korber | ASCI9 | Hymeneliaceae | |
| rimmed lichen | Aspicilia cingulata (Zahlbr.) Oksner | ASCI10 | Hymeneliaceae | |
| rimmed lichen | Aspicilia concinna (J. W. Thomson) | ASCO44 | Hymeneliaceae | |
| rimmed lichen | Aspicilia contigua (Lynge) J. W. Thomson | ASCO45 | Hymeneliaceae | |
| rimmed lichen | Aspicilia disserpens (Zahlbr.) Rasanen | ASDI11 | Hymeneliaceae | |
| rimmed lichen | Aspicilia elevata (Lynge) J. W. Thomson | ASEL10 | Hymeneliaceae | |
| rimmed lichen | Aspicilia fimbriata (H. Magn.) Clauzade & Rondon | ASFI6 | Hymeneliaceae | |
| rimmed lichen | Aspicilia gibbosa (Ach.) Korber | ASGI7 | Hymeneliaceae | |
| rimmed lichen | Aspicilia heteroplaca (Zahlbr.) Oksner | ASHE9 | Hymeneliaceae | |
| rimmed lichen | Aspicilia karelica (H. Magn.) Oksner | ASKA4 | Hymeneliaceae | |
| rimmed lichen | Aspicilia laevata (Ach.) Arnold | ASLA18 | Hymeneliaceae | |
| rimmed lichen | Aspicilia laxula (H. Magn.) Brodo | ASLA19 | Hymeneliaceae | |
| rimmed lichen | Aspicilia leprosescens (Sandst.) Hav. | ASLE23 | Hymeneliaceae | |
| rimmed lichen | Aspicilia limitata (H. Magn.) J. W. Thomson | ASLI12 | Hymeneliaceae | |
| rimmed lichen | Aspicilia mashiginensis (Zahlbr.) Oksner | ASMA18 | Hymeneliaceae | |
| rimmed lichen | Aspicilia mastoidea (Lynge) J. W. Thomson | ASMA19 | Hymeneliaceae | |
| rimmed lichen | Aspicilia narssaquensis (Lynge) J. W. Thomson | ASNA6 | Hymeneliaceae | |
| rimmed lichen | Aspicilia nikrapensis Darbish. | ASNI6 | Hymeneliaceae | |
| rimmed lichen | Aspicilia novae-semliae (Zahlbr.) Oksner | ASNO7 | Hymeneliaceae | |
| rimmed lichen | Aspicilia pergibbosa (H. Magn.) Rasanen | ASPE14 | Hymeneliaceae | |
| rimmed lichen | Aspicilia perradiata (Nyl.) Hue | ASPE15 | Hymeneliaceae | |
| rimmed lichen | Aspicilia pertusa (Lynge) J. W. Thomson | ASPE16 | Hymeneliaceae | |
| rimmed lichen | Aspicilia plicigera (Zahlbr.) Rasanen | ASPL60 | Hymeneliaceae | |
| rimmed lichen | Aspicilia reptans (Looman) Wetmore | ASRE12 | Hymeneliaceae | |
| rimmed lichen | Aspicilia rosulata Korber | ASRO7 | Hymeneliaceae | |
| rimmed lichen | Aspicilia ryrkaipiae (H. Magn.) Oksner | ASRY | Hymeneliaceae | |
| rimmed lichen | Aspicilia sorediza (Lynge) J. W. Thomson | ASSO8 | Hymeneliaceae | |
| rimmed lichen | Aspicilia sublapponica (Zahlbr.) Oksner | ASSU19 | Hymeneliaceae | |
| rimmed lichen | Aspicilia subplicigera (H. Magn.) Oksner | ASSU21 | Hymeneliaceae | |
| rimmed lichen | Aspicilia subradians (Nyl.) Hue | ASSU22 | Hymeneliaceae | |
| rimmed lichen | Aspicilia supertegens Arnold | ASSU23 | Hymeneliaceae | |
| rimmed lichen | Aspicilia tenuis (H. Magn.) | ASTE19 | Hymeneliaceae | |
| rimmed lichen | Aspicilia verrucigera Hue | ASVE12 | Hymeneliaceae | |
| rimrock milkvetch | Astragalus desperatus M.E. Jones | ASDE3 | Fabaceae | |
| rimrock milkvetch | Astragalus desperatus M.E. Jones var. conspectus Barneby | ASDEC | Fabaceae | |
| rimrock milkvetch | Astragalus desperatus M.E. Jones var. desperatus | ASDED | Fabaceae | |
| rimrock milkvetch | Astragalus desperatus M.E. Jones var. petrophilus M.E. Jones | ASDEP | Fabaceae | |
| Rincon manzanita | Arctostaphylos stanfordiana Parry ssp. decumbens (P.V. Wells) P.V. Wells | ARSTD4 | Ericaceae | |
| Rincon Mountain Indian paintbrush | Castilleja austromontana Standl. & Blumer | CAAU5 | Scrophulariaceae | |
| Rincon Mountain rockcress | Arabis tricornuta Rollins | ARTR6 | Brassicaceae | |
| Rincon Ridge ceanothus | Ceanothus confusus J.T. Howell | CECO6 | Rhamnaceae | |
| ringstem | Anulocaulis Standl. | ANULO | Nyctaginaceae | |
| Rio Abajo spleenwort | Asplenium corderoanum Proctor | ASCO35 | Aspleniaceae | |
| Rio Grande ayenia | Ayenia limitaris Cristobal | AYLI | Sterculiaceae | |
| Rio Grande beebrush | Aloysia macrostachya (Torr.) Moldenke | ALMA9 | Verbenaceae | |
| Rio Grande butterflybush | Buddleja sessiliflora Kunth | BUSE | Buddlejaceae | |
| Rio Grande ragweed | Ambrosia cheiranthifolia Gray | AMCH2 | Asteraceae | |
| Rio Grande sedge | Cyperus floribundus (Kük.) Carter & Jones | CYFL10 | Cyperaceae | |
| Rio Grande stickpea | Calliandra conferta Benth. | CACO | Fabaceae | |
| Rio Grande tickseed | Coreopsis nuecensoides E.B. Sm. | CONU6 | Asteraceae | |
| Rio Loc stickpea | Calliandra locoensis R. Garcia & D. Kolterman | CALO15 | Fabaceae | |
| ripgut brome | Bromus diandrus Roth | BRDI3 | Poaceae | |
| ripgut brome | Bromus diandrus Roth ssp. diandrus | BRDID2 | Poaceae | |
| ripgut brome | Bromus diandrus Roth ssp. rigidus (Roth) Lainz | BRDIR | Poaceae | |
| Ripley's gilia | Aliciella ripleyi (Barneby) J.M. Porter | ALRI3 | Polemoniaceae | |
| Ripley's milkvetch | Astragalus ripleyi Barneby | ASRI2 | Fabaceae | |
| Ripley's springparsley | Cymopterus ripleyi Barneby | CYRI2 | Apiaceae | |
| Ritter's coraldrops | Besseya ritteriana (Eastw.) Rydb. | BERI | Scrophulariaceae | |
| rival lipfern | Cheilanthes aemula Maxon | CHAE | Pteridaceae | |
| river birch | Betula nigra L. | BENI | Betulaceae | |
| river bottlebrush | Callistemon sieberi DC. | CASI17 | Myrtaceae | |
| river hawthorn | Crataegus rivularis Nutt. | CRRI | Rosaceae | |
| river junction hawthorn | Crataegus condigna Beadle | CRCO32 | Rosaceae | |
| river sheoak | Casuarina cunninghamiana Miq. | CACU8 | Casuarinaceae | |
| riverbank sedge | Carex stenoptila F.J. Herm. | CAST4 | Cyperaceae | |
| riverflat hawthorn | Crataegus opaca Hook. & Arn. | CROP | Rosaceae | |
| Riverside spineflower | Chorizanthe xanti S. Wats. | CHXA2 | Polygonaceae | |
| Riverside spineflower | Chorizanthe xanti S. Wats. var. leucotheca Goodman | CHXAL | Polygonaceae | |
| Riverside spineflower | Chorizanthe xanti S. Wats. var. xanti | CHXAX | Polygonaceae | |
| roadside agrimony | Agrimonia striata Michx. | AGST | Rosaceae | |
| roadside bittercress | Cardamine debilis D. Don | CADE14 | Brassicaceae | |
| roadside brome | Bromus stamineus Desv. | BRST3 | Poaceae | |
| roadside croton | Croton trinitatis Millsp. | CRTR8 | Euphorbiaceae | |
| roadside false madwort | Berteroa mutabilis (Vent.) DC. | BEMU | Brassicaceae | |
| roadside flatsedge | Cyperus sphacelatus Rottb. | CYSP3 | Cyperaceae | |
| roadside sandmat | Chamaesyce lasiocarpa (Klotzsch) Arthur | CHLA9 | Euphorbiaceae | |
| roadside windmill grass | Chloris sagraeana A. Rich. | CHSA3 | Poaceae | |
| Roan Mountain false goat's beard | Astilbe crenatiloba (Britt.) Small | ASCR7 | Saxifragaceae | |
| Roan Mountain sedge | Carex roanensis F.J. Herm. | CARO10 | Cyperaceae | |