Oberonia alipetala – synonym of Oberonia linearis
Oberonia condensata – synonym of Octarrhena angraecoides
Oberonia forcipifera – synonym of Oberonia cuneata
Oberonia gladiata – synonym of Phreatia gladiata
Oberonia hamadryas – synonym of Hippeophyllum hamadryas
Oberonia japenensis – synonym of Oberonia bifida
Oberonia micrantha – synonym of Phreatia micrantha
Oberonia microphylla – synonym of Oberonia microphylla
Oberonia myosurus – synonym of Phreatia matthewsii
Oberonia stenophylla – synonym of Oberonia linearis
Oberonia wariana – synonym of Oberonia lucida
Octarrhena albiflora – synonym of Phreatia albiflora
Octarrhena arfakensis – synonym of Octarrhena angraecoides
Octarrhena condensata – synonym of Octarrhena angraecoides
Octarrhena cylindrica – synonym of Octarrhena cylindrica
Octarrhena cylindrica J.J.Sm. var. major – synonym of Octarrhena cylindrica
Octarrhena filiformis brachyphylla
Octarrhena flava – synonym of Octarrhena angraecoides
Octarrhena longicaulis – synonym of Phreatia longicaulis
Octarrhena myosurus – synonym of Phreatia matthewsii
Octarrhena papuana – synonym of Phreatia papuana
Octarrhena semiorbicularis – synonym of Phreatia semiorbicularis
Octarrhena sphaerocarpa – synonym of Thelasis sphaerocarpa
Octarrhena suborbicularis – synonym of Octarrhena lorentzii
Octomeria stellata – synonym of Eria javanica
Octomeria vaginata – synonym of Eria javanica
Odontochilus hatusimanus – synonym of Rhomboda lanceolata
Odontochilus pomrangianus – synonym of Rhomboda lanceolata
Oeceoclades pulchra – synonym of Eulophia pulchra
Ophrys lancea – synonym of Herminium lanceum
Ophrys spiralis – synonym of Spiranthes sinensis
Orchiodes celebicum – synonym of Goodyera rubicunda
Orchiodes grande – synonym of Goodyera rubicunda
Orchiodes polygonoides – synonym of Rhomboda polygonoides
Orchiodes pusillum – synonym of Goodyera pusilla
Orchiodes rubicundum – synonym of Goodyera rubicunda
Orchiodes viridiflorum – synonym of Goodyera viridiflora
Orchis strateumatica – synonym of Zeuxine strateumatica
Orchis triplicata – synonym of Calanthe triplicata
Ornithochilus moretonii – synonym of Robiquetia flexa
Orsidice amplexicaulis – synonym of Thrixspermum amplexicaule
Orsidice lilacina – synonym of Thrixspermum amplexicaule
Ortmannia cernua – synonym of Geodorum densiflorum
Osyricera ovata – synonym of Bulbophyllum obyrnei
Oxyanthera abbreviata – synonym of Thelasis abbreviata
Oxyanthera carinata – synonym of Thelasis carinata
Oxyanthera decurva – synonym of Thelasis micrantha
Oxyanthera elata – synonym of Thelasis carinata
Oxyanthera micrantha – synonym of Thelasis micrantha
Oxyanthera papuana – synonym of Thelasis carinata
Oxysepalum ovalifolium – synonym of Bulbophyllum clandestinum
Oxystophyllum atropurpureum – synonym of Dendrobium atropurpureum