Taxon delimitation and genetic similarities of the Sphagnum imbricatum complex, as revealed by enzyme electrophoresis

Isozyme electrophoretic studies were used to assess genetic variation in the Sphagnum imbricatum complex in a sample of 1332 plants from 39 populations from western Europe, eastern North America and Japan. Mean pairwise genetic distance among populations clustered and depicted in a UPGMA phenogram correspond to the recognition of four species, viz. Sphagnum portoricense, S. affine, S. imbrication and S. austinii. The mean pairwise genetic identity among conspecific populations were 0.976, 0.847 and 0.841 for S. austinii, S. affine and S. portoricense, respectively. The mean pairwise genetic identity among taxa was 0.525 (S. austinii-S. affine), 0.476 (S. affine-S. portoricense), 0.600 (S. affine-S. imbricatum), 0.484 (S. imbricatum-S. austinii), 0.629 (S. imbricatum-S. portoricense) and 0.285 (S. austinii-S. portoricense). Populations of S. austinii in Europe are found to be genetically eroded (Hs = 0.001 +/- 0.000), (P-95 = 0.00). probably due to severe bottlenecks caused by a series of founder effects during postglacial migration from a limited number of glacial refugia in S.W. Europe. The mean genetic diversity of S. affine (Hs = 0.122 +/- 0.020) is at the same level as up to now reported for the more variable congeneric species. Among individuals of S. affine, 0.27% displayed mixed markers, indicating that, on rare occasions, hybridization may occur between S. affine and S. austinii. Preliminary genetic analysis of S. steerei supports the recognition of this taxon.