The polyphyletic evolution of oil secreting flowers among angiosperms and the pollination of orchids by oil collecting bees have been proposed to be successful evolutionary strategies. In this study, we explore variation in floral oil composition among neotropical orchids of the subtribe Oncidiinae and a malpighiaceous species (Byrsonima crassifolia). Many Oncidium species are thought to be mimics of malpighiaceous species because members of both groups flower simultaneously and have functionally similar inflorescences, thus attracting and sharing similar pollinators. Here, we compare the chemistry of oil compounds in these groups and provide insight into the radiation of oil related compounds and their relationship with oil collecting bees. Floral oil composition among orchid species were analyzed by gas chromatography/mass spectrometry (gc/ms). Mass spectra of significant peaks were compared among species of the same genus and among different orchid genera. We provide a major survey of oil components with over a hundred different major compounds for members of the Oncidiinae, a subtribe with the most diverse type of pollination systems found in the Orchidaceae. Our results show both quantitative and qualitative differences among orchid genera, but mainly quantitative differences within genera. The variability in oil chemistry found among different genera of orchids can be used to understand the exploitation of oil resources by oil collecting bees and could potentially explain the high degree of pollinator specificity for many tropical orchid species.

Key words: bee pollination, oil collecting bees, oil flowers, Oncidiinae