Three new synonyms of Macromitrium japonicum Dozy & Molk. (Bryophyta, Orthotrichaceae) based on morphological and molecular evidence

Macromitrium japonicum Dozy & Molk. is an epiphytic moss mainly recorded from East Asia. To clarify its morphological variations and their potential genetic basis, we morphologically compared fourteen samples assigned to M. japonicum, and constructed a phylogenetic tree including these samples based on trnL-F, trnG and ITS2. On the phylogenetic tree, these fourteen samples formed a single clade, being characterized by the typical features of M. japonicum. Comparing the types of M. japonicum var. makinoi (Broth.) Nog., M. dickasonii Bartr. and M. polygonostomum Dixon & P. de la Varde with these samples, and the types of M. japonicum and its former synonyms including Dasymitrium incurvum Lind. and M. bathyodontum Cardot, we found that the variations of the former three species fall within the morphological variation range of the above fourteen samples and the types of M. japonicum, D. incurvum and M. bathyodontum. Therefore, we treated M. japonicum var. makinoi, M. dickasonii and M. polygonostomum as three new synonyms of M. japonicum. Macromitrium giraldii Müll.Hal. is excluded from the synonyms of M. japoncium and likely an acceptable species name. Additionally, M. japonicum is newly recorded for Myanmar.