A further tessera in the two-centuries-old debate on the Hypnum cupressiforme complex (Hypnaceae, Bryopsida)

Taxonomic arrangement of Hypnum species has been controversial since the beginning of the nineteenth century. The molecular pattern and phylogenetic relationships within the Hypnum cupressiforme complex, in relation to other pleurocarps species, were investigated by study of nuclear ribosomal ITS1/ITS2 and chloroplast trnLUAA intron sequences. Seven Hypnum species from different continents were sequenced and analysed, with a relatively large set of pleurocarpous mosses. Sequences indicate a low level of genetic differentiation within the complex. Both maximum parsimony and maximum likelihood analyses indicate that Hypnum s.l. is distributed in several clades of pleurocarps; in addition, H. cupressiforme sensu strictu, and the complex, are not monophyletic. Our results clearly circumscribe only two species, H. jutlandicum and H. imponens; phylogenetic analyses, in particular, highlight the isolation of the latter from the complex. Genetic lineages with a clear geographic structure were found in Eurasia; these probably originated during the last glaciations. The presence of H. cupressiforme in some related clades flanking the other species examined supports the occurrence of an ongoing speciation within the complex.