Taxonomic and morphometric comments on Macromitrium tosae Besch (Orthotrichaceae), with its four new synonyms

Macromitrium tosae Besch. and M. cavaleriei Cardot & Ther. are two taxa that are poorly discriminated from one another, and M. melanostomum Paris & Broth., M. courtoisii Broth. & Paris, M. cylindrothecium Nog. and M. chungkingense P. C. Chen are four little known species. Cluster and Principle Component Analyses were applied to evaluate the morphological distinctiveness of these species based on 27 character indices of leaf morphology from ten type specimens and 17 other specimens. Macromitrium cylindrothecium, M. chungkingense, M. courtoisi and M. melanostomum are not unambiguously distinct from M. tosae and should therefore be considered conspecific. Macromitrium tosae, a common species in China, differs, however, from M. cavaleriei by shorter, lingulate, apiculate branch leaves with obtuse apices and distinctly pluri-papillose laminal cells, and its inner perichaetial leaves with acuminate or short acuminate apices.