The chemical composition of the floral extract of Epipogium aphyllum Sw. (Orchidaceae): A clue for their pollination biology

Abstract

Epipogium aphyllum is a rare European obligate mycoheterotrophic orchid lacking chlorophyll. It has not been studied previously with respect to pollination biology. We studied the association between the composition of floral scent emission and its pollination systems. Field observation indicates that the main pollinators of Epipogium aphyllum are representatives of the genus Bombus (Hymenoptera), B. lucorum, B. hortorum, B. terrestris, B. pascuorum and B. proteus, and the genus Apis (Hymenoptera) namely A. mellifera. The main potential vector (observed to accidentally carry pollen), is most likely Episyrphus balteatus (Diptera, Syrphidae). The chemical composition of the floral extracts of 4 populations of Epipogium aphyllum Sw. growing naturally in Poland and the Czech Republic was examined by gas chromatography coupled with mass spectrometry (GC-MS) and high-performance liquid chromatography coupled with diode-array detection and electrospray ionization mass spectrometry (LC-ESI-MS) techniques. According to GC-MS analysis, 9-tricosene, nonadecane, 1-nonadecene and nonacosane predominated in the floral extracts. The studied samples were also characterized by relatively high amounts of benzenoids, e.g. methyl cinnamate, which is known as an attractant to the males of various orchid bees. LC-ESI-MS revealed the presence of flavor compounds such as vanillin (4-hydroxy-3-methoxybenzaldehyde) and its derivative acetovanillone, together with higher amounts of aliphatic and phenolic acids. Additionally, we detected the presence of indole and morphine derivatives.