Ophrys annae and Ophrys chestermanii: an impossible love between two orchid sister species

The biological concept of species is founded on the presence of barriers that limit the gene flow and species delimitation represents a vivid topic in orchids. Studies on reproductive isolation in Mediterranean orchids often examine gene flow between co‐occuring species providing a relevant understanding of how species boundaries are maintained. In the sexually deceptive Ophrys genus, the role of postmating barriers has been traditionally tought to be weak and, despite the relevant morphological and ethological differences, low phylogenetic diversity has been recorded. In contrast, not many studies are focused on the relevance of each barriers in closely related species in island condition. Using a morphological approach and experimental crosses to evaluate postmating barriers, here, we clarify the taxonomic position of two sardinian endemic orchid sister‐species, Ophrys annae and O. chestermanii, currently ascribed in the bornmuelleri group. In Ophrys, due their hyper specialized pollination syndrome, premating barriers are often considered more relevant than postmating barriers. We found that the two endemisms differ sustantially in 16 functional traits adopted. We further detected asymmetric results in manual crosses suggesting that postmating barriers may act as reinforcement of the premating barriers. Our results suggest that in closely related orchid species of the Ophrys genus, gene flow is limited also by postmating barriers which have a relevant act in keeping the two reproductively isolated.