Establishing species distributions in large tropical plant genera: insights from twelve new Thai records of Oberonia (Orchidaceae)

Establishing species distributions is particularly challenging in large tropical genera of inconspicuous plants. One such genus is Oberonia (Orchidaceae) which we are currently revising for Thailand. When encountering material of a putatively new species, great care has been taken to make a wide geographic search for matching extra-Thai taxa. Against this background, we here record 12 species as new for Thailand: O. dissitiflora, O. evrardii, O. gracilis, O. insectifera, O. lotsyana, O. microphylla, O. orbicularis, O. semifimbriata, O. singalangensis, O. stenophylla, O. suborbicularis, O. wenzelii. Seven records are based (at least in part) on older collections, suggesting that many gaps in currently known species distributions can be filled through revision of existing collections alone. Our wide geographic search for taxonomic matches had three important implications: 1) we succeeded in identifying five species that had not previously been recognized for Thailand or neighbouring regions; 2) we realized that circumscription of three species should be widened, with implications for their known distributions; 3) comparison of numerous collections enabled us to report additionally six new records (O. evrardii for Myanmar; O. insectifera for Papua New Guinea; O. semifimbriata for Borneo; O. wenzelii for India, Myanmar and Java). Eventually, we draw attention to new online tools and resources that facilitate improvements of taxonomic and geographic knowledge in large tropical genera.