Tabula Rasa After All? Botanical Evidence for Ice-Free Refugia in Scandinavia Reviewed

The three botanical main components of the earlier arguments for ice-free refugia in Scandinavia the endemic alpine element, the 'West Arctic element', and the special disjunctions are reconsidered. New knowledge about evolutionary rates and geological conditions are brought in. The method proposed by Haldane, introducing the unit darwin, is applied to the Papaver radicatum complex. The conclusion is that the rates of evolution may have been underestimated in earlier literature on the subject. Isolation of small populations during a period of 10-15,000 years might be sufficient to explain the endemisms. Postglacial immigration by long-distance dispersal is regarded as the most probable explanation for the West Arctic element, with drifting ice, icebergs or migratory birds as probable dispersal vectors. The alternative hypothesis of preglacial immigration via a North Atlantic landbridge with subsequent survival in ice-free refugia, carries with it an unlikely evolutionary rigidity in Scandinavian alpine plants, and is therefore regarded as not very probable.