Long‐distance dispersal and barriers shape genetic structure of peatmosses (Sphagnum) across the Northern Hemisphere

Abstract Aim Disjunctly distributed peatmosses (Sphagnum) have been found to exhibit little genetic structure over regional and intercontinental scales, mainly caused by high ability for transoceanic long‐distance dispersal. Although, most Northern Hemisphere peatmoss species have wide circumboreal/nemoral ranges, little is known about the magnitude and effects of long‐distance dispersal and barriers in shaping the genetic structure of such species. We investigate whether high dispersal capacity has caused genetic homogeneity across broad areas of the Northern Hemisphere, or whether barriers act to shape genetic structure across different species with similar distributional ranges. Location Northern Hemisphere. Methods We studied genetic variation and structure in six Sphagnum species using 19 microsatellite loci. Results Four out of six species were genetically structured in similar ways; with mainly one Beringian and one Atlantic group. Overall, both the North American and Eurasian continents seemed to act as a barrier to gene flow in several species. However, the most abrupt breakpoint between genetic groups was found in south‐east Alaska. Main conclusions We found evidence for extensive gene flow between regions across the Northern Hemisphere among peatmosses, with oceans seemingly acting as weaker barriers to gene flow than landmasses. Plants from the amphi‐Atlantic and amphi‐Beringian regions of several species were genetically differentiated. Similar genetic structuring across several species, indicate that spore‐producing species do not disperse freely across their entire distributional range, but are likely limited by wind directions, landmass barriers and/or habitat availability.