Population structure and taxonomy of Sphagnum cuspidatum and S. viride

Abstract. Based on morphology Sphagnum cuspidatum and S. viride have been recognised as two different species. Morphs corresponding to the two taxa were investigated in nine populations situated in Norway, Denmark, Canada and USA. Eleven putative isozyme loci were used to map genetic variation, and to assess the taxonomic relationships. Cluster analysis of allele frequency data did not produce groups corresponding either to the two species or to geographic 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 showed significant divergence between the two morphs in one population, indicating that they might be reproductively isolated. However, in five other populations containing both morphs no such patterns were found, suggesting that the speciation process is incomplete. A species level recognition of these taxa is not supported by isozyme data. Rather taxonomic recognition at the subspecific level may be more appropriate. A population of S. trinitense expressed unique allele combinations, supporting the view that it is a distinct species different from S. cuspidatum.