Comparative floral micromorphology in four sympatric species of Serapias (Orchidaceae)

A great variety of colours, shapes, scents, energy-rich rewards and other floral traits form an integrated system that increases pollination efficiency or reduces pollen loss. Flowers lacking energetic rewards possess a more elaborate morphology to ensure co-specific pollination. Despite the prevalence of deceptive species among Euro-Mediterranean orchids, the study of their floral micromorphology is still in its infancy. In this work, we examine the floral micromorphology of four sympatric species of the widespread Mediterranean genus Serapias. Electron microscopy (scanning, transmission) was performed on flowers of four sympatric species of the deceptive genus Serapias, the widespread S.cordigera, S.lingua, S.parviflora and S.vomeracea. Each species has a characteristic combination of specialized, secretory epidermal cells and trichomes on the labellum and, to a lesser extent, the petals. Serapias lingua is highly specialized in that it produces olfactory signals and has two types of trichome with secretory apical cells, one of which is also present in S.parviflora. In addition to striated, conical secretory cells, S.cordigera and S.vomeracea also have characteristic, atypical secretory trichomes with bilobulate or dome-like protuberances. The labellar micromorphology of S.lingua and S.parviflora is adapted for scent production, whereas S.vomeracea and S.cordigera possess trichomes that may also provide visual and/or tactile cues. Owing to the combined effect of the specific floral fragrance and labellar micromorphology in pollinator selection, the pollination ecology of Serapias spp. is even more specialized than previously thought. © 2012 The Linnean Society of London.