Oplismenus undulatifolius (Ard.) P.Beauv. (Synonym : Orthopogon undulatifolius (Ard.) Spreng.)

Family : Poaceae

Oplismenus undulatifolius (Ard.) P.Beauv. var. elongatus Honda (Synonym : Oplismenus undulatifolius (Ard.) P.Beauv. f. elongatus (Honda) Y.N.Lee)

Family : Poaceae

Oplismenus undulatifolius (Ard.) P.Beauv. var. japonicus (Steud.) Koidz. (Synonym : Oplismenus undulatifolius (Ard.) P.Beauv. var. undulatifolius f. japonicus (Steud.) T.Koyama ex W.T.Lee)

Family : Poaceae

Oplopanax elatus (Nakai) Nakai (Synonym : Echinopanax elatus Nakai)

Family : Araliaceae

Opuntia monacanthos (Willd.) Haw. (Synonym : Opuntia monacanthos (Willd.) Haw. var. deflexa Salm-Dyck)

Family : Cactaceae [Naturalized plant]

Oreocnide frutescens (Thunb.) Miq. (Synonym : Urtica frutescens Thunb.)

Family : Urticaceae

Oreorchis patens (Lindl.) Lindl. (Synonym : Oreorchis patens (Lindl.) Lindl. var. gracilis (Franch. & Sav.) Makino ex Schltr.)

Family : Orchidaceae

Oreorchis patens (Lindl.) Lindl. subsp. coreana (Finet) Y.N.Lee (Synonym : Oreorchis coreana Finet)

Family : Orchidaceae

Orixa japonica Thunb. (Synonym : Othera orixa Lam.)

Family : Rutaceae

Orobanche coerulescens Stephan ex Willd. (Synonym : Orobanche ammophila C.A.Mey.)

Family : Orobanchaceae