New species or infraspecific variation? A case study of Ptychanthus striatus var. motuoensis var. nov. (Marchantiophyta: Lejeuneaceae) from Xizang, China

An unusual specimen of the genus Ptychanthus (Lejeuneaceae) was collected in Xizang, differing from the common P. striatus in the perianth, having only five, wing-like keels (one dorsal, two lateral and two ventral), the lateral and ventral keels being sharper than the dorsal one. Molecular-phylogenetic analysis of chloroplast and nuclear DNA sequences showed that the plant was deeply nested within P. striatus. As the differences in perianth structure could not be attributed to plasticity, we interpret the phylogenetic position of the plant as the result of a recent speciation process and describe it as a new variety, P. striatus var. motuoensis.