Considerable numbers of species have become extinct before being scientifically described, and the loss of natural habitats is known to be one of the major reasons for biodiversity declines. In this study, an endangered new species, Cayratia cheniana L. M. Lu & J. Wen, endemic to the limestone mountains of Ninh Thuan province of Vietnam is herein described based on both morphological and molecular evidence. With five chloroplast markers, Cayratia cheniana is placed as the first diverged lineage of Cayratia Juss. Morphologically, Cayratia cheniana shares synapomorphies with all other Cayratia s. s. in possessing a membrane enclosing ventral infolds in the seeds and presence of bracts on the lower part of the inflorescence axis. This species can be readily distinguished from other congeners by its tripalmate-trifoliate to bipinnate leaf architecture and stems with shredding bark.