Genetic structure of the Sphagnum magellanicum (Sphagnaceae) complex in Europe

Sphagnum magellanicum has historically been interpreted as a widespread species across both the Northern and Southern Hemispheres. Recent research, however, indicates that it comprises at least seven phylogenetic species, and that S. magellanicum s.str. is restricted to southern Argentina and Chile. Four species are recorded from North America and two of them, S. divinum and S. medium, are known to occur in Europe (and are typified by European collections). Here we assess European plants of this complex to test if two apparent North American endemics, S. diabolicum and S. magniae, occur in Europe, and document the genetic structure of European species of the complex, including gametophyte sex ratios and patterns of genetic diversity. We further assess evidence for gene flow between the species in Europe, and between North American and European plants of species that occur on both continents. Molecular data, especially ddRADseq, were used to assess genetic and phylogenetic patterns, and additional plants were identified with barcode markers to document European geographic distributions. The results indicate that S. diabolicum and S. magniae are endemic to North America. In Europe, S. divinum is more genetically diverse than S. medium. Sex ratios in both species did not depart from 50:50. Low levels of interspecific gene flow between the two species occur in Europe, as well as higher levels of gene flow between North American and European plants within S. divinum and S. medium. Overall, our results corroborate evidence that S. divinum and S. medium are phylogenetically distinct species and represent separate gene pools despite low levels of introgression.