Morphological variation in Thamnobryum alopecurum and its related species

The genus Thamnobryum (Musci) is distributed widely in temperate regions of the world, centered in East Asia. This genus comprises 55 species (Crosby 2000), most of which show a robust habit. There are currently known to occur 6 species and 4 varieties after revision by Noguchi (1981). However, there still remains some difficulty to understand Japanese species, since species of the genus show a wide range of variation. We attempted a taxonomic revision of the Japanese species of the genus, and found that the papillose leaf cells, which have ever known to occur only in T. coreanum, are also occasionally occur in T. alopecurum and T. neckeroides, and that some taxonomic confusion seems to have been caused by this papillose leaf cells. The Japanese species with papillose leaf cells can be distinguished by the combination of the following features: (1) cell shape at the area between leaf-tip and above cota-tip, (2) leaf-shape and the thickness of walls from leaf base, (3) thickness of cells-walls of stem-and branch-cortex, and (4) the molecular phylogenetic position based on ITS regions. Finally, 8 species including one new species were found to occur in Japan.