Incongruent phylogeographies in spite of similar morphology, ecology, and distribution:: Phippsia algida and P-concinna (Poaceae) in the North Atlantic region

Phylogeographic and taxonomic relationships among 54 North Atlantic populations of the snowbed grass genus Phippsia were investigated based on isozymes and genetically based morphological variation. The results support recognition of two distinct species, P. algida and P. concinna, the latter with at least two subspecies. Both of these self-fertilizing arctic pioneer species were genetic allotetraploids almost without intrapopulational variation. The two species showed strikingly different phylogeographies in the North Atlantic region in spite of their similarity in morphology, habitat ecology mating system, and dispersal ecology, and in spite of their present cooccurrence in many geographic areas, sometimes even in the same snowbeds. The same electrophoretic multilocus phenotype was observed in all populations of P. algida, and although this species showed considerable morphological variation, the variation was unstructured geographically Thus, P. algida showed a pattern similar to other arctic species investigated in the North Atlantic region; it has probably dispersed postglacially across the sea barriers among Greenland, Svalbard, Iceland, and Scandinavia. In contrast, P. concinna was virtually fixed for different multilocus phenotypes in the three main geographic areas analyzed (S Norway, Svalbard, Greenland), corresponding to fairly distinct divergence in morphology. This pattern suggests absence of postglacial among-area dispersal of P. concinna in spite of all of its similarities with its congener; it may have immigrated to the North Atlantic from different source areas and/or survived the last glaciation in situ.