Molecular phylogeny of Helleborus (Ranunculaceae), with an emphasis on the East Asian-Mediterranean disjunction

Phylogenetic relationships within the genus Helleborus (Ranunculaceae) were evaluated with analyses of plastid trnL-F and partial matK and nuclear ITS DNA sequences for all 16 currently recognised species in addition to several subspecies and geographical variants. The molecular study provides strong support for the monophyly of Helleborus. However, both traditional divisions of the genus, into two groups (Caulescentes and Scapigeri) or two subgenera (Helleborastrum and Helleborus), are refuted. All six currently recognised sections (Dicarpon, Chenopus, Griphopus, Helleborus, Helleborastrum, and Syncarpus) are monophyletic, four by default because they are monospecific. Section Dicarpon (H. thibetanus) is strongly supported as sister group to section Helleborastrum and could therefore be sunk into that section. Relationships between this pair of sections and the other sections are, however, not clear. At the specific level, all species which are clearly distinct morphologically are also distinct in terms of molecular divergence, but relationships between the poorly differentiated species in section Helleborastrum are not resolved with any degree of support. Using a molecular clock based on matK sequence divergence, the disjunction of H. thibetanus and section Helleborastrum between East Asia and the Mediterranean is tentatively dated at approximately 23 million years (middle Miocene), which corresponds well with the geological history of the area where H. thibetanus occurs.