Middletonia tiepiana (Gesneriaceae), a new species from southern Vietnam

A new species of Middletonia (Gesneriaceae), M. tiepiana, is described from Nui Chua National Park in southern Vietnam. This is the third species of the genus recorded in Vietnam, and notably, the second Vietnamese species with a blue corolla - a trait previously observed in M. evrardii (Vietnam), M. changjiangensis, and M. hainanensis (both from China). Middletonia tiepiana differs from the Vietnamese species by its leaves lacking interpetiolar ridges, shorter peduncles, linear and minute bracts, free glandular anthers dehiscing by apical pores, and from the Chinese congeners by its growth form, distinct leaf morphology, length of peduncles, deep blue-violet corolla with a white base, and absence of staminodes. It grows in sandstone-based soils within coastal semi-arid forest, a habitat not previously associated with the genus. A detailed morphological description, illustration, notes on distribution, ecology, and phenology, and a provisional conservation assessment are provided. A key to all known Middletonia species is also included.