PHYLOGENETIC RELATIONSHIPS WITHIN PLAGIOMNIUM SECTION ROSULATA

Abstract

  We scored a total of 16 morphological characters for all eight species of the ingroup, Plagiomnium section Rosulata, and for the outgroup, Plagiomnium section Undulata. A formal cladistic analysis was performed on the resulting data matrix using the computer programs MacClade and PAUP. The single most parsimonious tree was 20 steps long and, excluding uninformative characters, had a consistency index of 0.765 and a homoplasy index of 0.235. The topology of the tree agreed well with Koponen's (1971) “assumed phylogeny” of the group, especially with respect to the two major subgroups: (1) a “sharp-toothed” clade consisting of P. ellipticum, P. insigne, P. medium, and P. curvatulum; and (2) a “blunt-toothed” clade consisting of P. affine, P. tezukae, P. ciliare, and P. elatum. Omitting the two allopolyploid species (P. medium and P. curvatulum) from the analysis had no influence on the overall topology of the tree. Comparing the tree to patterns of relationships based on genetic distance, it was apparent that the species of the “blunt-toothed” subgroup were more strongly divergent inter se. It is speculated that these species may have originated longer ago than those of the “sharp-toothed” subgroup, which seems to be of very recent origin, especially P. medium. In addition, the “blunt-toothed’ species may have been more strongly affected by Pleistocene glaciation.