Chemical diversity of floral volatiles in Asclepiadoideae-Asclepiadeae (Apocynaceae)

Floral volatiles of 15 plant species from 8 genera (Cynanchum, Funastrum, Gonolobus, Metastelma, Oxypetalum, Orthosia, Sarcostemma, and Vincetoxicum) of the Apocynaceae-Asclepiadoideae tribe Asclepiadeae were investigated to get a better understanding of the odor chemistry, and of the role of odors in pollinator attraction. Floral volatiles were collected via headspace adsorption and analysed by GC–MS (gas chromatography–mass spectrometry). Of the 170 volatile compounds detected, 128 were identified, most of which are widespread floral scent compounds known from many different plant species. The species can be divided into two main groups: (1) species dominated by monoterpenoids (linalool, Z/E-ocimene), and (2) species dominated by benzenoids (benzaldehyde, phenylacetaldehyde, 2-phenylethyl acetate). Species of both chemotypes are pollinated mainly by Hymenoptera and Lepidoptera, and possibly these insects are effectively attracted by both monoterpenoids and benzenoids; alternatively, benzenoid-dominated plant species might attract a different subset of pollinators than the monoterpenoid-dominated plants.