Rhinanthus plants found in calcareous fens on Gotland (Sweden): Are they related to Rhinanthus osiliensis from Saaremaa (Estonia)?

Rhinanthus osiliensis is a narrow endemic growing in calcareous spring fens on the island Saaremaa, Estonia. Plants very similar to R. osiliensis have been found in Sweden on the island of Gotland. Fifteen microsatellite markers were used to characterize genetic variation within R. osiliensis and the unknown taxon from Gotland. Results were compared with common Rhinanthus minor and Rhinanthus angstifolius. Our results showed that genetic diversity was remarkably lower in the Rhinanthus sp. from Gotland compared to Estonian endemic R. osiliensis. The microsatellite loci we used distinguished four studied species. In total, 46 species-specific alleles were found. The Neighbor-Joining dendrogram based on Nei's genetic distances, the Bayesian clustering analysis and the principle coordinate analysis showed that R. osiliensis and Rhinanthus sp. from Gotland are genetically differentiated and could not be the same species. In addition, endemic R. osiliensis was closer to widespread R. angustifolius. Further genetic comparison between unknown Rhinanthus sp. and local R. angustifolius and R. minor from Gotland is necessary for determine the species status and checking the possible alternative hypothesis about the origin of the unclear taxon.