What do floral anatomy and micromorphology tell us about Neotropical Bulbophyllum section Didactyle (Orchidaceae: Bulbophyllinae)?

Bulbophyllum section Didactyle comprises seven species, but distinction between these is often problematic. These species are pollinated by milichiid flies and air currents move the hinged labellum and press the pollinator against the gynostemium. The labellum structure is considered to be homogeneous and conservative for the genus. Therefore, the floral anatomy and micromorphology of B. section Didactyle were studied in order to identify characters useful for distinguishing the species. All species have sunken glandular trichomes on the abaxial surface of the sepals (possible osmophores) and a trilobed labellum, clothed with trichomes, with a secretory cavity in the callus that is bound by scale-like papillae. Of the c. 100 characters assessed, 25 varied between species, and each pair of species differed by at least four character states, mainly occurring on the labellum. The data presented allow for a distinction to be made between species and corroborates their grouping in B. section Didactyle, as proposed previously. The presence of osmophores and a nectary on the labellum is confirmed, although their structure is more diverse than anticipated. Moreover, structural differences between B. weddellii and the core of the section might be the result of the odour-mediated attraction of pollinators rather than flower morphology and thus phylogeny. (C) 2014 The Linnean Society of London