| Symbol | Scientific name | Common name/Accepted name (for synonyms) | Family |
| OERUT | Oenothera runcinata (Engelm.) Munz var. typica Munz | Oenothera pallida ssp. runcinata | Onagraceae
|
| OERU3 | Oenothera runcinata (Engelm.) Munz | Oenothera pallida ssp. runcinata | Onagraceae
|
| OERY | Oenothera rydbergii House | Oenothera villosa ssp. strigosa | Onagraceae
|
| OESCB | Oenothera scapoidea Nutt. ex Torr. & Gray ssp. brachycarpa Raven | Camissonia scapoidea ssp. brachycarpa | Onagraceae
|
| OESCM | Oenothera scapoidea Nutt. ex Torr. & Gray ssp. macrocarpa Raven | Camissonia scapoidea ssp. macrocarpa | Onagraceae
|
| OESCU | Oenothera scapoidea Nutt. ex Torr. & Gray ssp. utahensis Raven | Camissonia scapoidea ssp. utahensis | Onagraceae
|
| OESCE | Oenothera scapoidea Nutt. ex Torr. & Gray var. eastwoodiae Munz | Camissonia eastwoodiae | Onagraceae
|
| OESCP | Oenothera scapoidea Nutt. ex Torr. & Gray var. purpurascens S. Wats. | Camissonia claviformis ssp. integrior | Onagraceae
|
| OESCS | Oenothera scapoidea Nutt. ex Torr. & Gray var. seorsa (A. Nels.) Munz | Camissonia scapoidea ssp. scapoidea | Onagraceae
|
| OESCT | Oenothera scapoidea Nutt. ex Torr. & Gray var. tortilis Jepson | Camissonia walkeri ssp. tortilis | Onagraceae
|
| OESC2 | Oenothera scapoidea Nutt. ex Torr. & Gray | Camissonia scapoidea ssp. scapoidea | Onagraceae
|
| OESED | Oenothera serrulata Nutt. ssp. drummondii (Torr. & Gray) Munz | Calylophus berlandieri ssp. berlandieri | Onagraceae
|
| OESEP | Oenothera serrulata Nutt. ssp. pinifolia (Engelm. ex Gray) Munz | Calylophus berlandieri ssp. pinifolius | Onagraceae
|
| OESET | Oenothera serrulata Nutt. var. typica Munz | Calylophus serrulatus | Onagraceae
|
| OESE3 | Oenothera serrulata Nutt. | Calylophus serrulatus | Onagraceae
|
| OESE2 | Oenothera sessilis (Pennell) Munz | Oenothera pilosella ssp. sessilis | Onagraceae
|
| OESI2 | Oenothera simsiana auct. non Ser. | Oenothera elata ssp. hirsutissima | Onagraceae
|
| OESP | Oenothera spachiana Torr. & Gray | Spach's evening-primrose | Onagraceae
|
| OESPC | Oenothera speciosa Nutt. var. childsii (Bailey) Munz | Oenothera speciosa | Onagraceae
|
| OESP2 | Oenothera speciosa Nutt. | pinkladies | Onagraceae
|
| OESPH | Oenothera specuicola Raven ssp. hesperia Raven | Camissonia specuicola ssp. hesperia | Onagraceae
|
| OESP3 | Oenothera specuicola Raven | Camissonia specuicola ssp. specuicola | Onagraceae
|
| OEST | Oenothera stricta Ledeb. ex Link | Chilean evening-primrose | Onagraceae
|
| OESTC2 | Oenothera strigosa (Rydb.) Mackenzie & Bush ssp. canovirens (Steele) Munz | Oenothera villosa ssp. villosa | Onagraceae
|
| OESTC | Oenothera strigosa (Rydb.) Mackenzie & Bush ssp. cheradophila (Bartlett) Munz | Oenothera villosa ssp. strigosa | Onagraceae
|
| OEST3 | Oenothera strigosa (Rydb.) Mackenzie & Bush | Oenothera villosa ssp. strigosa | Onagraceae
|
| OESTP | Oenothera strigulosa (Fisch. & C.A. Mey.) Torr. & Gray var. pubens S. Wats. | Camissonia pubens | Onagraceae
|
| OEST4 | Oenothera strigulosa (Fisch. & C.A. Mey.) Torr. & Gray | Camissonia strigulosa | Onagraceae
|
| OESU | Oenothera subacaulis (Pursh) Garrett | Camissonia subacaulis | Onagraceae
|
| OETA3 | Oenothera tanacetifolia Torr. & Gray | Camissonia tanacetifolia ssp. tanacetifolia | Onagraceae
|
| OETA2 | Oenothera taraxacoides (Woot. & Standl.) Munz | Oenothera flava ssp. taraxacoides | Onagraceae
|
| OETEG | Oenothera tetragona Roth ssp. glauca (Michx.) Munz | Oenothera fruticosa ssp. glauca | Onagraceae
|
| OETEB | Oenothera tetragona Roth var. brevistipata (Pennell) Munz | Oenothera fruticosa ssp. fruticosa | Onagraceae
|
| OETEF | Oenothera tetragona Roth var. fraseri (Pursh) Munz | Oenothera fruticosa ssp. glauca | Onagraceae
|
| OETEH | Oenothera tetragona Roth var. hybrida (Michx.) Fern. | Oenothera fruticosa ssp. glauca | Onagraceae
|
| OETEL2 | Oenothera tetragona Roth var. latifolia (Rydb.) Fern. | Oenothera fruticosa ssp. glauca | Onagraceae
|
| OETEL | Oenothera tetragona Roth var. longistipata (Pennell) Munz | Oenothera fruticosa ssp. fruticosa | Onagraceae
|
| OETER | Oenothera tetragona Roth var. riparia (Nutt.) Munz | Oenothera fruticosa ssp. fruticosa | Onagraceae
|
| OETES | Oenothera tetragona Roth var. sharpii Munz | Oenothera fruticosa ssp. fruticosa | Onagraceae
|
| OETEV | Oenothera tetragona Roth var. velutina (Pennell) Munz | Oenothera fruticosa ssp. fruticosa | Onagraceae
|
| OETE4 | Oenothera tetragona Roth | Oenothera fruticosa ssp. glauca | Onagraceae
|
| OETE2 | Oenothera tetraptera Cav. | fourwing evening-primrose | Onagraceae
|
| OETE3 | Oenothera texensis Raven & Parnell | Texas evening-primrose | Onagraceae
|
| OETO | Oenothera toumeyi (Small) Tidestrom | Calylophus toumeyi | Onagraceae
|
| OETR4 | Oenothera trichocalyx Nutt. | Oenothera pallida ssp. trichocalyx | Onagraceae
|
| OETR2 | Oenothera triloba Nutt. | stemless evening-primrose | Onagraceae
|
| OETUF | Oenothera tubicula Gray var. filifolia Eastw. | Calylophus hartwegii ssp. filifolius | Onagraceae
|
| OETU2 | Oenothera tubicula Gray | Calylophus tubicula | Onagraceae
|
| OEVIC2 | Oenothera villosa Thunb. ssp. canovirens (Steele) W. Dietr. & Raven | Oenothera villosa ssp. villosa | Onagraceae
|
| OEVIC | Oenothera villosa Thunb. ssp. cheradophila (Bartlett) W. Dietr. & Raven | Oenothera villosa ssp. strigosa | Onagraceae
|
| OEVIS | Oenothera villosa Thunb. ssp. strigosa (Rydb.) W. Dietr. & Raven | hairy evening-primrose | Onagraceae
|
| OEVIV | Oenothera villosa Thunb. ssp. villosa | hairy evening-primrose | Onagraceae
|
| OEVIS2 | Oenothera villosa Thunb. var. strigosa (Rydb.) Dorn | Oenothera villosa ssp. strigosa | Onagraceae
|
| OEVI | Oenothera villosa Thunb. | hairy evening-primrose | Onagraceae
|
| OEWAT | Oenothera walkeri (A. Nels.) Raven ssp. tortilis (Jepson) Raven | Camissonia walkeri ssp. tortilis | Onagraceae
|
| OEWA | Oenothera walkeri (A. Nels.) Raven | Camissonia walkeri ssp. walkeri | Onagraceae
|
| OEWO | Oenothera wolfii (Munz) Raven, W. Dietr. & Stubbe | Wolf's evening-primrose | Onagraceae
|
| OEXY | Oenothera xylocarpa Coville | woodyfruit evening-primrose | Onagraceae
|
| OENOT | Oenothera L. | evening-primrose | Onagraceae
|
| OGAR | Oglifa arizonica (Gray) Chrtek & Holub | Filago arizonica | Asteraceae
|
| OGAR2 | Oglifa arvensis (L.) Cass. | Logfia arvensis | Asteraceae
|
| OGCA | Oglifa californica (Nutt.) Rydb. | Filago californica | Asteraceae
|
| OGDE | Oglifa depressa (Gray) Chrtek & Holub | Filago depressa | Asteraceae
|
| OGGA | Oglifa gallica (L.) Chrtek & Holub | Logfia gallica | Asteraceae
|
| OGMI | Oglifa minima (Sm.) Reichenb. | Logfia minima | Asteraceae
|
| OKHY | Okenia hypogaea Schlecht. & Cham. | burrowing four o'clock | Nyctaginaceae
|
| OKENI | Okenia Schlecht. & Cham. | okenia | Nyctaginaceae
|
| OLAC | Oldenlandia acerosa (Gray) Gray | Houstonia acerosa | Rubiaceae
|
| OLANF | Oldenlandia angustifolia (Michx.) Gray var. filifolia Chapman | Hedyotis nigricans var. nigricans | Rubiaceae
|
| OLAN | Oldenlandia angustifolia (Michx.) Gray | Hedyotis nigricans var. nigricans | Rubiaceae
|
| OLBO | Oldenlandia boscii (DC.) Chapman | Bosc's mille graines | Rubiaceae
|
| OLCA | Oldenlandia callitrichoides Griseb. | Oldenlandiopsis callitrichoides | Rubiaceae
|
| OLCO | Oldenlandia corymbosa L. | flat-top mille graines | Rubiaceae
|
| OLFA | Oldenlandia fasciculata (Bertol.) Small | Oldenlandia uniflora | Rubiaceae
|
| OLGR | Oldenlandia greenei Gray | Hedyotis greenei | Rubiaceae
|
| OLHU | Oldenlandia humifusa (Gray) Gray | Houstonia humifusa | Rubiaceae
|
| OLLA2 | Oldenlandia lancifolia (Schumacher) DC. | calycose mille graines | Rubiaceae
|
| OLPUT | Oldenlandia purpurea (L.) Gray var. tenuifolia (Nutt.) Gray ex Chapman | Houstonia longifolia | Rubiaceae
|
| OLRU | Oldenlandia rubra (Cav.) Gray | Houstonia rubra | Rubiaceae
|
| OLSA | Oldenlandia salzmannii (DC.) Benth. & Hook. f. ex B.D. Jackson | Salzmann's mille graines | Rubiaceae
|
| OLSU2 | Oldenlandia subviscosa C. Wright ex Gray | Houstonia subviscosa | Rubiaceae
|
| OLUN | Oldenlandia uniflora L. | clustered mille graines | Rubiaceae
|
| OLDEN | Oldenlandia L. | oldenlandia | Rubiaceae
|
| OLCA4 | Oldenlandiopsis callitrichoides (Griseb.) Terrell & W.H. Lewis | creeping-bluet | Rubiaceae
|
| OLDEN2 | Oldenlandiopsis Terrell & W.H. Lewis | creeping-bluet | Rubiaceae
|
| OLAF | Olea africana Miller | Olea europaea ssp. africana | Oleaceae
|
| OLCH | Olea chrysophylla Lam. | Olea europaea ssp. africana | Oleaceae
|
| OLEUA | Olea europaea L. ssp. africana (P. Mill.) P. Green | African olive | Oleaceae
|
| OLEUE | Olea europaea L. ssp. europaea | European olive | Oleaceae
|
| OLEU | Olea europaea L. | olive | Oleaceae
|
| OLEA | Olea L. | olive | Oleaceae
|
| OLAR | Oleandra articulata (Sw.) K. Presl | oleander fern | Dryopteridaceae
|
| OLNO | Oleandra nodosa (Willd.) K. Presl | Oleandra articulata | Dryopteridaceae
|
| OLEAN | Oleandra Cav. | oleander fern | Dryopteridaceae
|
| OLAL3 | Olearia allomii T. Kirk | daisy bush | Asteraceae
|
| OLCH2 | Olearia cheesmanii Cockayne & Allan | daisy bush | Asteraceae
|
| OLEAR | Olearia Moench | daisy bush | Asteraceae
|
| OLCE | Olfersia cervina (L.) Kunze | woodland islandfern | Dryopteridaceae
|
| OLFER | Olfersia Raddi | islandfern | Dryopteridaceae
|
| OLLI | Oligomeris linifolia (Vahl) J.F. Macbr. | lineleaf whitepuff | Resedaceae
|
| OLIGO | Oligomeris Camb. | oligomeris | Resedaceae
|