| Symbol | Scientific name | Common name/Accepted name (for synonyms) | Family |
| UNSE2 | Uniola sessiliflora Poir. | Chasmanthium sessiliflorum | Poaceae
|
| UNSP2 | Uniola spicata L. | Distichlis spicata | Poaceae
|
| UNVI2 | Uniola virgata (Poir.) Griseb. | Leptochloopsis virgata | Poaceae
|
| UNIOL | Uniola L. | seaoats | Poaceae
|
| URSE4 | Urachne setosa Trin. | Piptochaetium setosum | Poaceae
|
| URPI4 | Uralepis pilosa Buckl. | Erioneuron pilosum | Poaceae
|
| URAC | Urceolaria actinostoma Ach. | Diploschistes actinostomus | Thelotremataceae
|
| URAL | Urceolaria albissima (Ach.) Fink | Diploschistes diacapsis | Thelotremataceae
|
| UREX | Urceolaria exotica J.F. Gmel. | Schradera exotica | Rubiaceae
|
| URSC | Urceolaria scruposa (Schreber) Ach. | Diploschistes scruposus | Thelotremataceae
|
| URLUS | Urechites lutea (L.) Britt. var. sericea R.W. Long | Pentalinon luteum | Apocynaceae
|
| URLU | Urechites lutea (L.) Britt. | Pentalinon luteum | Apocynaceae
|
| URPI2 | Urechites pinetorum Small | Pentalinon luteum | Apocynaceae
|
| URLOS | Urena lobata L. ssp. sinuata (L.) Waalkes | Urena sinuata | Malvaceae
|
| URLOS2 | Urena lobata L. var. sinuata (L.) Miq. ex Kuntze | Urena sinuata | Malvaceae
|
| URLO | Urena lobata L. | Caesarweed | Malvaceae
|
| URSI | Urena sinuata L. | burrmallow | Malvaceae
|
| URTR | Urena trilobata Vell. | Urena lobata | Malvaceae
|
| URENA | Urena L. | urena | Malvaceae
|
| URBA | Urera baccifera (L.) Gaud. | scratchbush | Urticaceae
|
| URCA2 | Urera caracasana (Jacq.) Gaud. ex Griseb. | flameberry | Urticaceae
|
| URCH2 | Urera chlorocarpa Urban | ortiga | Urticaceae
|
| URGL | Urera glabra (Hook. & Arn.) Weddell | hopue | Urticaceae
|
| URKA | Urera kaalae Wawra | opuhe | Urticaceae
|
| URKO | Urera konaensis St. John | Urera glabra | Urticaceae
|
| UROB | Urera obovata Benth. | urera | Urticaceae
|
| URSAK | Urera sandvicensis Weddell var. kauaiensis Rock | Urera glabra | Urticaceae
|
| URSAM | Urera sandvicensis Weddell var. mollis Weddell | Urera glabra | Urticaceae
|
| URSA | Urera sandvicensis Weddell | Urera glabra | Urticaceae
|
| URERA | Urera Gaud. | urera | Urticaceae
|
| URMA2 | Urginea maritima (L.) Baker | red squill | Liliaceae
|
| URSC2 | Urginea scilla Steinh. | Urginea maritima | Liliaceae
|
| URGIN | Urginea Steinh. | liverseed grass | Liliaceae
|
| URAD | Urochloa adspersa (Trin.) R. Webster | Dominican signalgrass | Poaceae
|
| URAR | Urochloa arizonica (Scribn. & Merr.) O. Morrone & F. Zuloaga | Arizona signalgrass | Poaceae
|
| URAR2 | Urochloa arrecta (Hack. ex T. Dur. & Schinz) O. Morrone & F. Zuloaga | African signalgrass | Poaceae
|
| URBR2 | Urochloa brizantha (C. Hochstetter ex A. Rich.) R. Webster | palisade signalgrass | Poaceae
|
| URCI | Urochloa ciliatissima (Buckl.) R. Webster | fringed signalgrass | Poaceae
|
| URFAR | Urochloa fasciculata (Sw.) R. Webster var. reticulata (Torr.) R. Webster | Urochloa fasciculata | Poaceae
|
| URFA | Urochloa fasciculata (Sw.) R. Webster | browntop signalgrass | Poaceae
|
| URMA3 | Urochloa maxima (Jacq.) R. Webster | guineagrass | Poaceae
|
| URMO80 | Urochloa mosambicensis (Hack.) Dandy | African liverseed grass | Poaceae
|
| URMU | Urochloa mutica (Forsk.) T.Q. Nguyen | para grass | Poaceae
|
| UROL | Urochloa oligobrachiata (Pilger) Kartesz, comb. nov. ined. | weak signalgrass | Poaceae
|
| URPA | Urochloa panicoides Beauv. | panic liverseed grass | Poaceae
|
| URPI3 | Urochloa piligera (F. Muell. ex Benth.) R. Webster | wattle signalgrass | Poaceae
|
| URPL | Urochloa plantaginea (Link) R. Webster | plantain signalgrass | Poaceae
|
| URPL2 | Urochloa platyphylla (Munro ex Wright) R. Webster | broadleaf signalgrass | Poaceae
|
| URPL3 | Urochloa platytaenia (Stapf) Crins | Urochloa oligobrachiata | Poaceae
|
| URRA | Urochloa ramosa (L.) Nguyen | dixie signalgrass | Poaceae
|
| URRE2 | Urochloa reptans (L.) Stapf | sprawling signalgrass | Poaceae
|
| URRU | Urochloa ruziziensis (Germ. & Evrard) Crins | Urochloa brizantha | Poaceae
|
| URSU2 | Urochloa subquadripara (Trin.) R. Webster | tropical signalgrass | Poaceae
|
| URTE2 | Urochloa texana (Buckl.) R. Webster | Texas signalgrass | Poaceae
|
| URUN | Urochloa uniseta J. Presl | Ixophorus unisetus | Poaceae
|
| URVI2 | Urochloa villosa (Lam.) T. Q. Nguyen | hairy signalgrass | Poaceae
|
| UROCH | Urochloa Beauv. | signalgrass | Poaceae
|
| URLI5 | Uropappus lindleyi (DC.) Nutt. | Lindley's silverpuffs | Asteraceae
|
| URLI2 | Uropappus linearifolius Nutt. | Uropappus lindleyi | Asteraceae
|
| UROPA | Uropappus Nutt. | silverpuffs | Asteraceae
|
| URPI | Urospermum picroides (L.) Scop. ex F.W. Schmidt | prickly goldenfleece | Asteraceae
|
| UROSP | Urospermum Scop. | urospermum | Asteraceae
|
| URAQ | Urostachys aqualupianus (Spring) Herter | Huperzia aqualupiana | Lycopodiaceae
|
| URCH4 | Urostachys chinensis (Christ) Herter ex Nessel | Huperzia chinensis | Lycopodiaceae
|
| URDI2 | Urostachys dichotomus (Jacq.) Herter | Huperzia dichotoma | Lycopodiaceae
|
| URER | Urostachys erubescens (Brack.) Herter ex Nessel | Huperzia erubescens | Lycopodiaceae
|
| URFU | Urostachys funiformis (Cham. ex Spring) Herter | Huperzia funiformis | Lycopodiaceae
|
| URHA | Urostachys haleakalae (Brack.) Herter | Huperzia haleakalae | Lycopodiaceae
|
| URHE | Urostachys �helleri (Herter) Herter ex Nessel | Huperzia helleri | Lycopodiaceae
|
| URLI | Urostachys linifolius (L.) Herter | Huperzia linifolia | Lycopodiaceae
|
| URLUP | Urostachys lucidulus (Michx.) Herter ex Nessel var. porophilus (Lloyd & Underwood) Herter ex Nessel, non Lam. | Huperzia porophila | Lycopodiaceae
|
| URLU2 | Urostachys lucidulus (Michx.) Herter ex Nessel | Huperzia lucidula | Lycopodiaceae
|
| URMI | Urostachys miyoshiana (Makino) Herter ex Nessel | Huperzia chinensis | Lycopodiaceae
|
| URNU | Urostachys nutans (Brack.) Herter ex Nessel | Huperzia nutans | Lycopodiaceae
|
| URPH | Urostachys phyllanthus (Hook. & Arn.) Herter | Huperzia phyllantha | Lycopodiaceae
|
| URPO3 | Urostachys polytrichoides (Kaulfuss) Herter ex Nessel | Huperzia polytrichoides | Lycopodiaceae
|
| URPO2 | Urostachys porophilus (Lloyd & Underwood) Herter ex Nessel | Huperzia porophila | Lycopodiaceae
|
| URPO | Urostachys portoricensis (Underwood & Lloyd) Herter | Huperzia acerosa | Lycopodiaceae
|
| URRE | Urostachys reflexus (Lam.) Herter | Huperzia reflexa | Lycopodiaceae
|
| URSE5 | Urostachys selago (L.) Herter ex Nessel | Huperzia selago var. selago | Lycopodiaceae
|
| URSE2 | Urostachys serratus (Thunb. ex Murr.) Herter | Huperzia serrata var. serrata | Lycopodiaceae
|
| URSI2 | Urostachys sintenisii Herter | Huperzia sintenisii | Lycopodiaceae
|
| URSU | Urostachys sulcinervius (Spring) Herter ex Nessel | Huperzia sulcinervia | Lycopodiaceae
|
| URTA | Urostachys taxifolius (Sw.) Herter | Huperzia taxifolia | Lycopodiaceae
|
| URTE | Urostachys tenuicaulis (Underwood & Lloyd) Herter | Huperzia tenuicaulis | Lycopodiaceae
|
| URVE | Urostachys verticillatus auct. non (L. f.) Herter | Huperzia acerosa | Lycopodiaceae
|
| URWI | Urostachys wilsonii (Underwood & Lloyd) Herter | Huperzia wilsonii | Lycopodiaceae
|
| URAE | Urtica aestuans L. | Laportea aestuans | Urticaceae
|
| URBA2 | Urtica baccifera L. | Urera baccifera | Urticaceae
|
| URBA3 | Urtica ballotifolia Weddell | | Urticaceae
|
| URBR | Urtica breweri S. Wats. | Urtica dioica ssp. holosericea | Urticaceae
|
| URCA3 | Urtica californica Greene | Urtica dioica ssp. gracilis | Urticaceae
|
| URCA6 | Urtica canadensis L. | Laportea canadensis | Urticaceae
|
| URCA4 | Urtica caracasana Jacq. | Urera caracasana | Urticaceae
|
| URCA5 | Urtica cardiophylla Rydb. | Urtica dioica ssp. gracilis | Urticaceae
|
| URCHR | Urtica chamaedryoides Pursh var. runyonii Correll | Urtica chamaedryoides | Urticaceae
|
| URCH3 | Urtica chamaedryoides Pursh | heartleaf nettle | Urticaceae
|
| URCY | Urtica cylindrica L. | Boehmeria cylindrica | Urticaceae
|
| URDID | Urtica dioica L. ssp. dioica | stinging nettle | Urticaceae
|
| URDIG | Urtica dioica L. ssp. gracilis (Ait.) Seland. | California nettle | Urticaceae
|
| URDIH | Urtica dioica L. ssp. holosericea (Nutt.) Thorne | stinging nettle | Urticaceae
|