| Symbol | Scientific name | Common name/Accepted name (for synonyms) | Family |
| ORCA9 | Oryzopsis caduca Beal | × Achnella caduca | Poaceae
|
| ORCA5 | Oryzopsis canadensis (Poir.) Torr. | Piptatherum canadense | Poaceae
|
| ORCO3 | Oryzopsis contracta (B.L. Johnson) Schlechter | Achnatherum contractum | Poaceae
|
| OREX | Oryzopsis exigua Thurb. | Piptatherum exiguum | Poaceae
|
| ORHE | Oryzopsis hendersonii Vasey | Achnatherum hendersonii | Poaceae
|
| ORHO2 | Oryzopsis holciformis (M. Bieb.) Hackel | ricegrass | Poaceae
|
| ORHYC | Oryzopsis hymenoides (Roemer & J.A. Schultes) Ricker ex Piper var. contracta B.L. Johnson | Achnatherum contractum | Poaceae
|
| ORHY | Oryzopsis hymenoides (Roemer & J.A. Schultes) Ricker ex Piper | Achnatherum hymenoides | Poaceae
|
| ORKI | Oryzopsis kingii (Boland.) Beal | Ptilagrostis kingii | Poaceae
|
| ORMI2 | Oryzopsis micrantha (Trin. & Rupr.) Thurb. | Piptatherum micranthum | Poaceae
|
| ORMI3 | Oryzopsis miliacea (L.) Benth. & Hook. f. ex Aschers. & Schweinf. | Piptatherum miliaceum | Poaceae
|
| ORPU4 | Oryzopsis pungens (Torr. ex Spreng.) A.S. Hitchc. | Piptatherum pungens | Poaceae
|
| ORRA2 | Oryzopsis racemosa (Sm.) Ricker ex A.S. Hitchc. | Piptatherum racemosum | Poaceae
|
| ORSW | Oryzopsis swallenii C.L. Hitchc. & Spellenberg | Achnatherum swallenii | Poaceae
|
| ORWE | Oryzopsis webberi (Thurb.) Benth. ex Vasey | Achnatherum webberi | Poaceae
|
| ORYZO | Oryzopsis Michx. | ricegrass | Poaceae
|
| OSTE | Osmadenia tenella Nutt. | false rosinweed | Asteraceae
|
| OSMAD | Osmadenia Nutt. | osmadenia | Asteraceae
|
| OSAMA | Osmanthus americanus (L.) Benth. & Hook. f. ex Gray var. americanus | devilwood | Oleaceae
|
| OSAMM | Osmanthus americanus (L.) Benth. & Hook. f. ex Gray var. megacarpus (Small) P.S. Greene | devilwood | Oleaceae
|
| OSAM | Osmanthus americanus (L.) Benth. & Hook. f. ex Gray | devilwood | Oleaceae
|
| OSFL | Osmanthus floridanus Chapman | Osmanthus americanus var. americanus | Oleaceae
|
| OSFO | Osmanthus ×fortunei Carriere | Fortune`s osmanthus | Oleaceae
|
| OSFR2 | Osmanthus fragrans Lour. | sweet osmanthus | Oleaceae
|
| OSHE | Osmanthus heterophyllus (G. Don) P. S. Green | holly osmanthus | Oleaceae
|
| OSIL | Osmanthus ilicifolius (Hassk.) Mouillef. | Osmanthus heterophyllus | Oleaceae
|
| OSME2 | Osmanthus megacarpus (Small) Small ex Little | Osmanthus americanus var. megacarpus | Oleaceae
|
| OSSA | Osmanthus sandwicensis (Gray) Knobl. | Nestegis sandwicensis | Oleaceae
|
| OSMAN | Osmanthus Lour. | devilwood | Oleaceae
|
| OSCE2 | Osmaronia cerasiformis (Torr. & Gray ex Hook. & Arn.) Greene | Oemleria cerasiformis | Rosaceae
|
| OSBO | Osmia borinquensis Britt. | Chromolaena borinquensis | Asteraceae
|
| OSCO | Osmia corymbosa (Aubl.) Britt. & Wilson | Chromolaena corymbosa | Asteraceae
|
| OSFR | Osmia frustrata (B.L. Robins.) Small | Chromolaena frustrata | Asteraceae
|
| OSGE | Osmia geraniifolia (Urban) Britt. & Wilson | Chromolaena geraniifolia | Asteraceae
|
| OSIV | Osmia ivifolia (L.) Schultz-Bip. | Chromolaena ivifolia | Asteraceae
|
| OSOD | Osmia odorata (L.) Schultz-Bip. | Chromolaena odorata | Asteraceae
|
| OSSI | Osmia sinuata (Lam.) Britt. & Wilson | Chromolaena sinuata | Asteraceae
|
| OSAM2 | Osmorhiza ambigua (Gray) Coult. & Rose | Osmorhiza occidentalis | Apiaceae
|
| OSARB | Osmorhiza aristata (Thunb.) Makino & Yabe var. brevistylis (DC.) Boivin | Osmorhiza claytonii | Apiaceae
|
| OSARL | Osmorhiza aristata (Thunb.) Makino & Yabe var. longistylis (Torr.) Boivin | Osmorhiza longistylis | Apiaceae
|
| OSBE | Osmorhiza berteroi DC. | sweetcicely | Apiaceae
|
| OSBI | Osmorhiza bipartriata Constance & Shan | Osmorhiza mexicana ssp. bipartriata | Apiaceae
|
| OSBRF | Osmorhiza brachypoda Torr. var. fraterna Jepson | Osmorhiza brachypoda | Apiaceae
|
| OSBR | Osmorhiza brachypoda Torr. | California sweetcicely | Apiaceae
|
| OSBR2 | Osmorhiza brevipes (Coult. & Rose) Suksdorf | Osmorhiza berteroi | Apiaceae
|
| OSCHC | Osmorhiza chilensis Hook. & Arn. var. cupressimontana (Boivin) Boivin | Osmorhiza depauperata | Apiaceae
|
| OSCHP | Osmorhiza chilensis Hook. & Arn. var. purpurea (Coult. & Rose) Boivin | Osmorhiza purpurea | Apiaceae
|
| OSCH | Osmorhiza chilensis Hook. & Arn. | Osmorhiza berteroi | Apiaceae
|
| OSCL | Osmorhiza claytonii (Michx.) C.B. Clarke | Clayton's sweetroot | Apiaceae
|
| OSDE | Osmorhiza depauperata Phil. | bluntseed sweetroot | Apiaceae
|
| OSDI | Osmorhiza divaricata (Britt.) Suksdorf | Osmorhiza berteroi | Apiaceae
|
| OSLE | Osmorhiza leibergii (Coult. & Rose) Blankinship | Osmorhiza purpurea | Apiaceae
|
| OSLOB | Osmorhiza longistylis (Torr.) DC. var. brachycoma Blake | Osmorhiza longistylis | Apiaceae
|
| OSLOI | Osmorhiza longistylis (Torr.) DC. var. imbarbata Salamun | Osmorhiza longistylis | Apiaceae
|
| OSLOV | Osmorhiza longistylis (Torr.) DC. var. villicaulis Fern. | Osmorhiza longistylis | Apiaceae
|
| OSLO | Osmorhiza longistylis (Torr.) DC. | longstyle sweetroot | Apiaceae
|
| OSMEB | Osmorhiza mexicana Griseb. ssp. bipartriata (Constance & Shan) Lowry & A.G. Jones | Mexican sweetcicely | Apiaceae
|
| OSME3 | Osmorhiza mexicana Griseb. | Mexican sweetcicely | Apiaceae
|
| OSNU | Osmorhiza nuda Torr. | Osmorhiza berteroi | Apiaceae
|
| OSOB2 | Osmorhiza obtusa (Coult. & Rose) Fern. | Osmorhiza depauperata | Apiaceae
|
| OSOC | Osmorhiza occidentalis (Nutt. ex Torr. & Gray) Torr. | western sweetroot | Apiaceae
|
| OSPU | Osmorhiza purpurea (Coult. & Rose) Suksdorf | purple sweetroot | Apiaceae
|
| OSMOR | Osmorhiza Raf. | sweetroot | Apiaceae
|
| OSAD | Osmunda adiantifolia L. | Anemia adiantifolia | Anemiaceae
|
| OSCIC | Osmunda cinnamomea L. var. cinnamomea | cinnamon fern | Osmundaceae
|
| OSCIF | Osmunda cinnamomea L. var. frondosa Gray | Osmunda cinnamomea var. cinnamomea | Osmundaceae
|
| OSCIG | Osmunda cinnamomea L. var. glandulosa Waters | cinnamon fern | Osmundaceae
|
| OSCII | Osmunda cinnamomea L. var. imbricata (Kunze) Milde | cinnamon fern | Osmundaceae
|
| OSCI | Osmunda cinnamomea L. | cinnamon fern | Osmundaceae
|
| OSCL2 | Osmunda claytoniana L. | interrupted fern | Osmundaceae
|
| OSHI | Osmunda hirsuta L. | Anemia hirsuta | Anemiaceae
|
| OSRES | Osmunda regalis L. var. spectabilis (Willd.) Gray | royal fern | Osmundaceae
|
| OSRE | Osmunda regalis L. | royal fern | Osmundaceae
|
| OSRU | Osmunda ×ruggii R. Tryon | | Osmundaceae
|
| OSSP | Osmunda spicant L. | Blechnum spicant | Blechnaceae
|
| OSMUN | Osmunda L. | osmunda | Osmundaceae
|
| OSDO | Ossaea domingensis Cogn. | Sagraea scalpta | Melastomataceae
|
| OSKR | Ossaea krugiana Cogn. | Leandra krugiana | Melastomataceae
|
| OSSC | Ossaea scabrosa (L.) DC. | Sagraea scabrosa | Melastomataceae
|
| OSSC2 | Ossaea scalpta (Vent.) DC. | Sagraea scalpta | Melastomataceae
|
| OSAN | Osteomeles anthyllidifolia (Sm.) Lindl. | Hawai'i hawthorn | Rosaceae
|
| OSTEO | Osteomeles Lindl. | osteomeles | Rosaceae
|
| OSCA | Osteospermum calendulaceum L. f. | stinking roger | Asteraceae
|
| OSEC | Osteospermum ecklonis (DC.) Norl. | blue and white daisybush | Asteraceae
|
| OSFR4 | Osteospermum fruticosum (L.) Norl. | shrubby daisybush | Asteraceae
|
| OSUV | Osteospermum uvedalia L. | Smallanthus uvedalius | Asteraceae
|
| OSTEO2 | Osteospermum L. | daisybush | Asteraceae
|
| OSCH2 | Ostrya chisosensis Correll | Ostrya virginiana var. chisosensis | Betulaceae
|
| OSKN | Ostrya knowltonii Coville | Knowlton's hophornbeam | Betulaceae
|
| OSVIC | Ostrya virginiana (P. Mill.) K. Koch var. chisosensis (Correll) Henrickson, comb. nov. ined. | Chisos hophornbeam | Betulaceae
|
| OSVIL | Ostrya virginiana (P. Mill.) K. Koch var. lasia Fern. | Ostrya virginiana var. virginiana | Betulaceae
|
| OSVIV | Ostrya virginiana (P. Mill.) K. Koch var. virginiana | hophornbeam | Betulaceae
|
| OSVI | Ostrya virginiana (P. Mill.) K. Koch | hophornbeam | Betulaceae
|
| OSTRY | Ostrya Scop. | hophornbean | Betulaceae
|
| OTCA | Othake callosa (Nutt.) Bush | Palafoxia callosa | Asteraceae
|
| OTSP | Othake sphacelata (Nutt. ex Torr.) Rydb. | Palafoxia sphacelata | Asteraceae
|
| OTAU | Otophylla auriculata (Michx.) Small | Agalinis auriculata | Scrophulariaceae
|
| OTDE | Otophylla densiflora (Benth.) Small | Agalinis densiflora | Scrophulariaceae
|
| OTAL | Ottelia alismoides (L.) Pers. | ducklettuce | Hydrocharitaceae
|
| OTTEL | Ottelia Pers. | ottelia | Hydrocharitaceae
|
| OTRH | Ottoschulzia rhodoxylon (Urban) Urban | pincho palo de rosa | Icacinaceae
|