Orchis patens Desf.: seed morphology of an endangered Mediterranean orchid

The loss of orchid habitats has increased the investment on orchid conservation efforts to reduce the risk of extinction of rare species. In northwestern Italy, orchids are among the most threatened of all plant groups in the region, but little is known about the biology of most of the less abundant taxa. In this study, we used light and scanning electron microscopy to characterize the morphology of the seeds of the threatened Orchis patens Desf., a declining species present in semi-natural habitats. We found a marked positive relationship between seed size and embryo size that may be not restricted to O. patens but also occur in other orchid species. The comparative analysis of the observed seed traits revealed hidden morphological affinities at the reproductive level among O. patens and the three subspecies of O. mascula, showing the potential of this approach to test the taxonomic relationships among the different taxa included in the genus Orchis.