Phylogenetic relationships of the moss genus Pleurochaete Lindb. (Bryales: Pottiaceae) based on chloroplast and nuclear genomic markers

The phylogenetic relationships of the moss genus Pleurochaete was investigated using evidence from chloroplast and nuclear ribosomal DNA sequences (atpB-abcL spacer, rps4+rps4-trnS IGS, trnL-trnF region, and ITS1-5.8S-ITS2 region). Monophyly of Pleurochaete is confirmed, but the genus is nested within Tortella. Five highly supported clades, including Chionoloma, Pseudosymblepharis and Trichostomum tenuirostre, were found, partially corresponding to phytogeographic areas. However, denser sampling is needed to resolve subgeneric relationships. Within Pleurochaete three monophyletic clades were recovered: neotropical Pleurochaete luteola, European Pleurochaete squarrosa, and North American P. squarrosa. The relationships between and taxonomic status of these clades are not resolved. Our results point to two hypotheses to explain the current situation: (1) an ancient, wide distribution of P. squarrosa on the Laurasian continent, with a subsequent split into two genetically isolated clades and sympatric ecological isolation of P. luteola; and (2) a neotropical origin of the genus, followed by long-distance dispersal of P. squarrosa into Eurasia. In contrast to previous molecular studies on transatlantic bryophytes, no evidence was found of recent intercontinental gene flow in P. squarrosa. Consequently, the two genetically isolated but morphologically indistinguishable clades of P. squarrosa may represent a further example for either lineage sorting or cryptic speciation in mosses.