Molecular data of Sphagnum majus ssp. majus and ssp. norvegicum (Bryophyta: Sphagnaceae) relative to taxonomy and geography

Species delimitation is problematic in many plant groups and among the
mosses, Sphagnum is one of the more contentious genera because of high
levels of morphological variation. The allopolyploid species, Sphagnum
majus, comprises one such problematic complex. Two morphologically
differentiated but overlapping subspecies have been described. We
conducted morphometric and molecular analyses with samples from around the
Northern Hemisphere to test for phenotypic and phylogenetic
differentiation between the subspecies. Although field collections of the
two species can be statistically differentiated morphologically, there is
substantial overlap. Genome-scale molecular data do not suggest any
differentiation between S. majus ssp. majus and ssp. norvegicum, including
samples assigned to the two taxa from sympatric sites. Sequence data from
the plastid genome were employed to infer parentage of allopolyploid S.
majus. Our results support the hypothesis that S. annulatum is the
paternal parent and S. cuspidatum is the maternal parent.  We
conclude that the morphological differences between them are either
plastic responses to habitat heterogeneity or segregating genetic
variation within a single taxon. Formal taxonomic recognition of two taxa
is not supported by our molecular data.