POPULATION-STRUCTURE AND INTERSPECIFIC DIFFERENTIATION OF THE PEAT MOSS SISTER SPECIES SPHAGNUM-RUBELLUM AND SPHAGNUM-CAPILLIFOLIUM (SPHAGNACEAE) IN NORTHERN EUROPE

Isozyme electrophoresis was used to study the morphologically similar sister species Sphagnum rubellum and S. capillifolium from a sample of 1313 plants representing 37 populations from Scandinavia, Great Brita in and S Germany. The mean pairwise genetic identities (I) among consp ecific populations were 0.976 for S. rubellum and 0.969 for S. capilli folium, versus 0.627 between populations of the two species. Interspec ific gene flow was indicated by the observation of occasional plants i n sympatric populations with alleles otherwise unique to the other spe cies. Populations of bisexual S. capillifolium were significantly more variable than populations of unisexual S. rubellum. Alpine population s of S. rubellum and S. capillifolium were dominated by few genotypes, and differentiation among populations was pronounced, indicating a lo w level of sexual recombination. In S. rubellum, maximum variability w as found in western areas with high annual precipitation. Distribution of alleles in S. rubellum indicated restricted gene flow between Grea t Britain and Scandinavia. Postglacial migration from separate refugia may explain large-scale variation in S. rubellum.