Brachythecium wangianum (Brachytheciaceae, Bryophyta), a new species from Northern China and Southern Russia

Brachythecium wangianum (Brachytheciaceae), a new moss species from northern China and southern Russia, is described and illustrated. Combining morphological observations and phylogenetic analyses, this study clarifies the systematic placement of Chinese and Russian materials of this taxon, provides a full morphological description, and distinguishes it from other morphologically similar species of Brachythecium . Special attention is paid to comparison with the closely related congeners B. laetum (Brid.) Schimp. and B. boreale Ignatov, as well as the widespread and highly polymorphic B. salebrosum (Hoffm. ex F. Weber & D. Mohr) Schimp. and B. rotaeanum De Not. Phylogenetic analysis based on nrITS sequences strongly supports B. wangianum as a distinct species, sister to B. laetum (Brid.) Schimp. Morphologically, B. wangianum differs from B. laetum in having a longer, more slender leaf acumen, longer median laminal cells, and an autoicous sexual condition. Combined with morphological and phylogenetic evidence, the taxonomic status of B. wangianum is established, and its geographical distribution delineated. Detailed micrographs are also provided. The discovery of this new species enriches the species diversity of Brachythecium in China and Russia, and provides valuable data for future studies on the phylogeny and biogeography of Brachytheciaceae in temperate regions.