Floral scent chemistry and pollination in the Neotropical aroid genus Xanthosoma (Araceae)

Abstract

The Neotropical aroid genus Xanthosoma (Caladieae, Araceae) embraces about 140 species of tuberous herbs whose night-blooming inflorescences emit strong, pleasant floral scents, presumably involved in the atttaction of pollinators. The number of studies on the floral scent chemistry of aroids, as well as on their role in pollinator attraction, has undergone a considerable increase in the last decade. In Xanthosoma, however, neither have never been properly assessed. In the present study, we provide an overview on the reproductive and pollination biology of Xanthosoma species and add new reports on the pollinators of some species. Furthermore, we investigate the floral scent chemistry of 13 species through dynamic headspace sample collection and analysis by gas chromatography coupled to mass spectrometry (GC–MS). A thorough literature survey and novel data from our own personal findings revealed that floral visitors are known for only 12 species of Xanthosoma, which represent less than 10% of its currently documented species diversity. Cyclocephaline scarabs (Melolonthidae, Cyclocephalini) were reported in inflorescences of 11 of the 12 species and are assumed to be the main pollinators associated with them. A total of 76 VOCs, mainly terpenes and benzenoids, were detected. Floral scent bouquets diverge considerably among analyzed species of Xanthosoma mainly due to the presence of unique prominent compounds that ensure originality of the blends rather than because of their quantitative complexity (number of constituents), as analyzed samples were typically dominated by few (2–4) VOCs that together accounted for >80% of the total relative scent discharge. A number of these dominant VOCs had already been isolated in other species of aroids and reported as effective attractants of cyclocephaline scarabs in field biossays, namely (Z)-jasmone, p-vinylanisole and dihydro-β-ionone and we speculate that along with other dominant compounds they are directly involved in pollinator selection in Xanthosoma.