| Botanical Name |
Authority |
| Obregonia denegrii |
CITES |
| Ochanostachys spp. |
Parasitic |
| Ochlandra spp. |
NAPPRA |
| Ochrosia hleakalae |
ESA-E |
| Ochrosia kilaueaensis |
ESA-E |
| Octoknema spp. |
NAPPRA |
| Odontitella spp. |
Parasitic |
| Odontites spp. |
Parasitic |
| Oedina spp. |
Parasitic |
| Oenothera deltoides ssp. howellii |
ESA-E |
| Okoubaka spp. |
Parasitic |
| Olax spp. |
Parasitic |
| Oligoneuron (Solidago) houghtonii |
ESA-T |
| Oligostachyum spp. |
NAPPRA |
| Oliverella spp. |
Parasitic |
| Olmeca spp. |
NAPPRA |
| Ombrophytum spp. |
Parasitic |
| Omelocalamus (= Arundinaria) spp. |
NAPPRA |
| Omphacomeria spp. |
Parasitic |
| Omphalotrix spp. |
Parasitic |
| Oncella spp. |
Parasitic |
| Oncocalyx spp. |
Parasitic |
| Ongokea spp. |
Parasitic |
| Onobrychis vicifolia |
FSA-A |
| Onopardum acaulon |
NW |
| Onopardum illyricum |
NW |
| Ophiocephalus spp. (See: Castilleja spp.) |
Parasitic |
| Opilia spp. |
Parasitic |
| Opuntia aurantiaca |
NW |
| Opuntia treleasei |
ESA-E |
| Orcuttia californica |
ESA-E |
| Orcuttia inequalis |
ESA-T |
| Orcuttia pilosa |
ESA-E |
| Orcuttia tenuis |
ESA-T |
| Orcuttia viscida |
ESA-E |
| Oreiostachys (= Nastus) spp. |
Poa. |
| Oreobambus spp. |
NAPPRA |
| Oreocalamus (= Chimonobambusa) spp. |
NAPPRA |
| Oricia spp. |
Treatment |
| Oriciopsis spp. |
Treatment |
| Orixa spp. |
Treatment |
| Ornobrychis viciifolia |
FSA-A |
| Orobanche spp. (except bulbosa, californica, cooperi, corymbosa, dugesii, fasciculata, ludoviciana, multicaulis, parishii, pinorum, uniflora, valida, vallicola – these natives are acceptable) |
Parasitic |
| Orthantha spp. |
NW |
| Orthocarpus spp. |
Parasitic |
| Oryctanthus spp. |
Parasitic |
| Oryza spp. |
NAPPRA |
| Oryza barthii |
NAPPRA |
| Oryza longistaminata |
NW |
| Oryza punctata |
NW |
| Oryza rufipogon |
NW |
| Oryza sativa |
NAPPRA |
| Oryzopsis hymenoides |
FSA-A |
| Osmoxylon mariannense |
ESA-E |
| Osyridicarpos spp. |
Parasitic |
| Osyris spp. |
Parasitic |
| Otatea spp. |
NAPPRA |
| Othonna armiana (from S. Africa) |
CITES III |
| Othonna cacalioides (from S. Africa) |
CITES III |
| Othonna euphorbioides (from S. Africa) |
CITES III |
| Othonna retrorsa (from S. Africa) |
CITES III |
| Ottelia alismoides |
NW |
| Ottochloa nodosa |
NAPPRA |
| Ottoschulzia rhodoxylon |
ESA-T |
| Oxanthera spp. |
Treatment |
| Oxypolis canbyi |
ESA-E |
| Oxytenanthera spp. |
NAPPRA |
| Oxytropis campestris v. chartacea |
ESA-T |
