Abstract
Four species, including one newly described, of Japanese cleistocarpous species of Weissia (Pottiaceae): W. exserta, W. japonica, W. kiiensis and W. parajaponica sp. nov. are recognized based on molecular phylogenetic inference and morphological reassessment. For each species, typification, description, distribution, illustrations and photographs are presented, and a key to the species is included. Rapid sporophyte modifications in Weissia and monophyletic positions of these four species are supported by the analysis using concatenated chloroplast rbcL and rps4 gene sequences. A lectotype is designated for W. controversa which is the type species of the genus, and a new combination, W. loncophylla is proposed for Trachycarpidium lonchophyllum.