A review of Acromastigum (Lepidoziaceae, Marchantiophyta) in East Indochina.

Acromastigum A. Evans is revised in East Indochina. The distribution of six species is documented, including one species whose occurrence is not supported by available materials. One new-to-science species from the species-poor subgenus Acromastigum is described from the Lâm Viên Plateau of the Central Highlands of Vietnam. The report of Acromastigum curtilobum for Thailand is based on incorrect identification and should be referred to A. herzogii. Acromastigum echinatum and A. laevigatum are observed for the first time in Cambodia. A large number of new localities of A. herzogii have been found in Vietnam, where the species distribution extends from North Vietnam through the Annamite Range to the Lâm Viên Plateau. This species is the most common representative of the genus in East Indochina. Morphological and molecular data reveal a more natural relationship of A. herzogii and A. stellare to subg. Inaequilatera than to subg. Acromastigum, as previously suggested. These two subgenera are also distinct in their rhizoid distribution, which was not noted in previous research. Overall, Acromastigum is an uncommon component of plant communities in East Indochina and has never been found with either sporophytes or fertilized archegonia, suggesting its high sensitivity to disturbances in forest communities.