Monosolenium (Marchantiopsida) Penetrates the Paleotropics

East Asian <i>Monosolenium tenerum</i> is the only representative monotypic Monosoleniaceae and has been found for the first time in North Indochina in five provinces of Vietnam. All paleotropical localities, including those previously known in Indonesia, are situated not in the high mountains, as one might expect for the East Asian species occurring southward in East Asia, but in the lower altitude zones (i.e., in conditions physiognomically similar to where the species grows further north). A comparison of the bioclimatic parameters of locations where the species was found revealed clear similarities across all the Vietnamese localities of the species. The closest bioclimatic location to where the species has been found in Vietnam is in Nepal. The species reaches its greatest abundance in anthropogenically nitrified habitats, which may suggest that it is currently expanding to southern Indochina along the rural settlements in the catchments of the largest rivers and suggests that it may be discovered in Cambodia, Laos, and southern Vietnam in the near future.