Ocimum, Genus
Odontites, Genus
Oenanthe, Genus
Oenothera, Genus
Oleaceae, Family
Omphalodes, Genus
Onagraceae, Family
Onobrychis, Genus
Onoclea, Genus
Onocleaceae, Family
Ononis, Genus
Onopordum, Genus
Ophioglossaceae, Family
Ophioglossales, Order
Ophioglossum, Genus
Ophrys, Genus
Orchidaceae, Family
Orchis, Genus
Oreopteris, Genus
Origanum, Genus
Orlaya, Genus
Ornithogalum, Genus
Ornithopus, Genus
Orobanchaceae, Family
Orobanche, Genus
Orthilia, Genus
Osmunda, Genus
Osmundaceae, Family
Oxalidaceae, Family
Oxalidales, Order
Oxalis, Genus