Heterogeneous genetic structure in eastern North American peat mosses (Sphagnum)

Bryophytes generally have broad geographical ranges that suggest high dispersal ability. The aim of this study was to test hypotheses about dispersal limitation, as indicated by isolation by distance, in four spore-producing species of the moss genus Sphagnum (Sphagnum carolinianum, Sphagnum missouricum, Sphagnum macrophyllum and Sphagnum pylaesii) and to assess whether plants in the southern USA harbour high levels of unique alleles and/or other indicators of exceptional genetic diversity. Isolation by distance was detected in all four species, but regional patterns of genetic structure were very species specific. Northern and southern genotype groups were detected in S. carolinianum and S. missouricum, but in S. pylaesii plants from the Adirondack Mountains of New York were genetically distinct from others to the north and south. One species, S. macrophyllum, exhibited differentiation between northern and southern genetic groups that appeared to reflect more ancient phylogenetic diversification.