Phylogenetic and biogeographic analysis of the steppe plant Adonis vernalis

It is likely that the Pleistocene glacial and interglacial cycles led to alternate range expansion and mixing of more and less cold-resistant species of the present-day Euro-Siberian steppe. By genotyping populations from across the Euro-Siberian range of the pheasant's eye (Adonis vernalis), we aimed at gaining insight into the steppe florogenesis based on its species evolutionary history. Molecular dating based on three chloroplast loci and the nuclear internal transcribed spacer revealed a basal split within the A. vernalis-A. villosa-A. volgensis group at about 1.8 Ma. Although the primary area of origin of the species group is certainly in Asia, our results show that A. vernalis itself originated in southern Europe between about 1.8 and 0.9 Ma. A deep vicariance separates the Spanish populations from the Balkan and Carpathian populations in southeastern Europe . Our results suggest that A. vernalis migrated from the sub-Mediterranean forest-steppe zone in southeastern Europe to the continental forest-steppe zone. Thermophilic species such as A. vernalis do not seem to have survived in the cold deserts of the Last Glacial Maximum in southern Western Siberia, so this region was likely (re)colonized postglacially from the surroundings of the Ural Mountains. Pontic compared to Pannonian and extrazonal German populations have the highest private allelic richness. Overall, our results show the importance of the origin and ecological requirements with respect to temperature and humidity of steppe plants (e.g., thermophilic with, for steppe plants, high moisture requirements in A. vernalis versus eurythermal and adapted to severe drought) for the composition of the present steppe flora.