Circumarctic dispersal and long-distance colonization of South America: the moss genus Cinclidium

Aim Arctic plant phylogeography has largely focused on seed plants, and studies on other plant groups are necessary for comparison. Bryophytes have a unique life cycle and can be resistant to extreme conditions, suggesting that their phylogeographic patterns may differ from those of vascular plants. We address the history of the bryophyte genus Cinclidium in order to assess: (1) interspecific relationships, (2) whether its current broad circumarctic distribution results from recent dispersal or has been maintained by long-term local survival under severe glacial conditions, and (3) the origin of its bipolar disjunction. Location Arctic/boreal and bipolar. Methods We sequenced three plastid regions (atpHatpI, rpl32trnL and clpP1.1clpP1.2) in 129 accessions covering the entire geographical range of all four described species, and inferred phylogenetic relationships and phylogeographical patterns using maximum parsimony, statistical parsimony and Bayesian inference. Results Cinclidium subrotundum was inferred to be monophyletic, in agreement with its distinct morphology and ecology. The three remaining known species (the haploids C. latifolium and C. arcticum, and the diploid C. stygium) shared a number of closely related or identical haplotypes despite their clear morphological differentiation. In all species, identical haplotypes occurred across the entire circumpolar region, including North Atlantic islands. In the bipolar species C. stygium, the haplotype observed in South America (Tierra del Fuego) was identical to one found in Iceland. Three populations originally referred to C. latifolium harboured highly divergent haplotypes and may represent a new species. Main conclusions The extensive haplotype sharing suggests a polyploid origin of C. stygium from C. arcticum, as well as incomplete lineage sorting and/or hybridization between the two haploids C. arcticum and C. latifolium. We interpret the finding of identical haplotypes over vast areas, including isolated islands, as a result of recent dispersal causing the circumpolar distribution of all species in the Northern Hemisphere and the extreme bipolar disjunction in C. stygium. The patterns in the bryophyte genus Cinclidium resemble those previously documented in arcticalpine and bipolar vascular plants, suggesting that similar mechanisms have shaped species distributions in bryophytes and higher plants.