Gymnomitrion vietnamicum (Gymnomitriaceae, Marchantiophyta)-a new species from North Indochina

Gymnomitrion vietnamicum sp. nov. is described from the Hoang Lien Son Range (North Vietnam), the southernmost outpost of the Sino-Himalayan flora and vegetation, wedged into the Indochinese floristic region of the Paleotropic Kingdom. The species is morphologically similar to G. blankae recently described from the territorially adjacent region-Yunnan Province of China-but differs in the structure of the stem, shape of apices of the leaf lobes and shoot coloration. At the same time, this morphological similarity contrasts with relatively high genetic differences, which show that each of the species is more closely related to other taxa that are much more morphologically different from them. Thus, the morphological similarity of the two compared taxa (G. vietnamicum and G. blankae) may imply convergence. The described new species again confirms the leading role of the Sino-Himalayas as the taxonomic diversity center of the morphologically well-defined "Apomarsupella" group, phylogenetically deeply nested within Gymnomitrion. Gymnomitrion vietnamicum is one of the most southern representatives of this group.