Families (As per The Plant List)

O

Oleaceae - 14 ( Chionanthus ramiflorus, Fraxinus floribunda, Fraxinus micrantha, Fraxinus xanthoxyloides, Jasminum dispermum, Jasminum mesnyi, Jasminum nepalense, Ligustrum compactum, Ligustrum confusum, Ligustrum indicum, Ligustrum robustum, Olea europaea subsp cuspidata, Osmanthus insularis, Syringa emodi)

Onagraceae - 28 ( Circaea alpina subsp. micrantha, Circaea cordata, Circaea repens, Epilobium amurense, Epilobium angustifolium, Epilobium brevifolium, Epilobium brevifolium subsp. trichoneurum, Epilobium chitralense, Epilobium conspersum, Epilobium cylindricum, Epilobium gouldii, Epilobium latifolium, Epilobium laxum, Epilobium leiophyllum, Epilobium minutiflorum, Epilobium palustre, Epilobium parviflorum, Epilobium royleanum, Epilobium sikkimense, Epilobium speciosum, Epilobium stracheyanum, Epilobium tibetanum, Epilobium wallichianum, Epilobium wattianum, Epilobium williamsii, Fuchsia magellanica, Oenothera drummondii, Oenothera rosea)

Orchidaceae - 30 ( Anthogonium gracile, Arundina graminifolia, Bulbophyllum guttulatum, Calanthe davidii, Calanthe puberula, Cleisostoma schneideri, Coelogyne pendula, Cymbidium mastersii, Dendrobium eriiflorum, Dendrobium falconeri var. senapatianum, Dendrobium hookerianum, Epigeneium arunachalense, Eria hegdei, Goodyera biflora, Habenaria gibsonii var. foliosa, Habenaria marginata var. fusifera, Liparis udaii, Luisia balakrishnanii, Paphiopedilum spicerianum, Paphiopedilum spicerianum f. burkhardii, Pecteilis rawatii, Peristylus balakrishnanii, Platanthera edgeworthii, Pleione praecox, Polystachya seidenfadeniana, Vanda coerulea, Vanda coerulea f. luwangalba, Vanda motesiana, Vanilla sanjappae, Zeuxine chowdherii)

Orobanchaceae - 50 ( Aeginetia indica var. alba, Boschniakia himalaica, Centranthera cochinchinensis var. nepalensis, Gleadovia ruborum, Lathraea squamaria, Orobanche alba, Pedicularis albida, Pedicularis bicornuta, Pedicularis bifida, Pedicularis brevifolia, Pedicularis canescens, Pedicularis cheilanthifolia, Pedicularis gracilis, Pedicularis heydei, Pedicularis hoffmeisteri, Pedicularis hookeriana, Pedicularis klotzschii, Pedicularis longiflora, Pedicularis longiflora subsp. tubiformis, Pedicularis megalantha, Pedicularis mollis, Pedicularis nodosa, Pedicularis oederi, Pedicularis oederi subsp. oederi var. heteroglossa, Pedicularis ophiocephala, Pedicularis pectinata, Pedicularis pectinata var. rosea, Pedicularis pennelliana, Pedicularis porrecta, Pedicularis punctata, Pedicularis rhinanthoides, Pedicularis rhinanthoides subsp. labellata , Pedicularis rhinanthoides subsp. revoluta, Pedicularis roylei, Pedicularis siphonantha, Pedicularis tenuirostris, Pedicularis trichoglossa, Phtheirospermum glandulosum, Picrorhiza kurroa, Scrophularia calycina, Scrophularia decomposita, Scrophularia dentata, Scrophularia edgeworthii, Scrophularia elatior, Scrophularia himalensis, Scrophularia koelzii, Scrophularia obtusa, Scrophularia polyantha, Scrophularia variegata, Striga euphrasioides)

Oxalidaceae - 4 ( Oxalis corniculata, Oxalis debilis, Oxalis debilis var. corymbosa, Oxalis lasiandra)