Asian Mountain Toads (Ophryophryne) are a poorly known genus of mostly small-sized anurans from southeastern China and Indochina. To shed light on the systematics within this group, the most comprehensive mitochondrial DNA phylogeny for the genus to date is presented, and the taxonomy and biogeography of this group is discussed. Complimented with extensive morphological data (including associated statistical analyses), molecular data indicates that the Langbian Plateau, in the southern Annamite Mountains, Vietnam, is one of the diversity centres of this genus where three often sympatric species of Ophryophryne are found, O. gerti, O. synoria and an undescribed species. To help resolve outstanding taxonomic confusion evident in literature (reviewed herein), an expanded redescription of O. gerti is provided based on the examination of type material, and the distributions of both O. gerti and O. synoria are considerably revised based on new locality records. We provide the first descriptions of male mating calls for all three species, permitting a detailed bioacoustics comparison of the species. We describe the new species from highlands of the northern and eastern Langbian Plateau, and distinguish it from its congeners by a combination of morphological, molecular and acoustic characters. The new species represents one of the smallest known members of the genus Ophryophryne. At present, the new species is known from montane evergreen forest between 700-2200 m a.s.l. We suggest the species should be considered Data Deficient following IUCN's Red List categories.
Keywords: 12S rRNA; 16S rRNA; Da Lat Plateau; Indochina; Truong Son; advertisement call; amphibian; biodiversity; frog; southeast Asia; taxonomy.