Begonia barosma, a new species in Begonia sect. Coelocentrum (Begoniaceae) from limestone karsts across Sino-Vietnamese Border.

Begonia barosma, a new species in Begonia sect. Coelocentrum Irmscher (Begoniaceae) from limestone karsts across Sino-Vietnamese border is described in detail. It shows high similarities to the adjacently distributed B. lanternaria Irmscher, but differs from it in fleshy, relatively flat leaf blade with different pattern of variegation, sparsely pilose on abaxial surface of outer tepals. The molecular phylogenetic analysis based on ITS supports that the new species is a monophyletic lineage, separating from B. lanternaria Irmscher. Considering its small population size, narrow distribution, and disturbance by human activities, its conservation status is categorized as "Vulnerable (VU B1, B2 ab (iv, v), C2 a (i), D2)" according to the IUCN Red List Categories and Criteria. [ABSTRACT FROM AUTHOR]