Factors of divergence in co-occurring varieties of Dactylorhiza incarnata (Orchidaceae)

Due to often large variation in traits within and between populations, taxonomy of orchid species is problematic. In this study, we aim to assess the probability of sympatric speciation in mixed populations of nectarless Dactylorhiza incarnata varieties (incarnata, ochroleuca and cruenta). We conducted morphological, phenological and ecological measurements in five populations in Hiiumaa, western Estonia. In most populations, we did not find any differences to reveal genetic divergence between the varieties. In one population, however, differences in shoot and flower traits were found. This population also differed at the community level from the other four study populations. Composition of pollinator fauna on one hand, and the presence of rewarding companion species on the other, may cause selection to act towards different directions in different populations of nectarless species. In contrast to earlier studies with another nectarless orchid species, we found pollination success to be positively frequency-dependent, which may be caused by a stable pollinator preference for one of the varieties.