Population structure and taxonomy of Sphagnum cuspidatum and S-viride

Based on morphology, Sphagnum cuspidatum and S. viride have been recognized as two different species. Morphs corresponding to the two taxa were invest igated in nine populations situated in Norway, Denmark, Canada, and U.S.A. Eleven putative isozyme loci were used to map genetic variation and to asse ss the taxonomic relationships. Cluster analysis of allele frequency data d id not produce groups corresponding either to the two species or to geograp hic regions. Low evolutionary rates because of low mutation rates and large effective population sizes may account for the lack of divergence between populations, even across continents. A test of population differentiation s howed significant divergence between the two morphs in one population indic ating that they might be reproductively isolated. However, in five other po pulations containing both morphs no such patterns were found suggesting tha t the speciation process is incomplete. A species level recognition of thes e taxa is nor supported by isozyme data, rather taxonomic recognition at th e subspecific level may be more appropriate. A population of S. trinitense ex pressed unique allele combinations, supporting the view that it is a dis tinct species different from S. cuspidatum.