Lasiocarpus is a genus of bisexual, dioecious, or trioecious shrubs or small trees of Malpighiaceae endemic to the seasonally dry tropical forests of the Pacific slopes of Mexico. In this paper the monophyly of this genus is tested using a molecular phylogeny based on three plastid (ndhF, matK, rbcL) and a single nuclear (PHYC) markers that were newly sequenced for the three currently accepted species in this genus, along with representative taxa from the main phylogenetic groups previously recognized in Malpighiaceae. The three species of Lasiocarpus were retrieved in a well supported clade corroborating the monophyly of this genus. A taxonomic treatment of this genus is presented. Lasiocarpus ovalifolius is synonymized with L. salicifolius, and a new species, Lasiocarpus andersoniorum, endemic to Southern Mexico, is proposed. It is morphologically distinguished by characters such as axillary inflorescences, reflexed sepals, petals with crenate margin and strigose indumentum, large styles, and 2-lobed stigmas. The taxonomic revision includes morphological descriptions and distribution maps for the three accepted species of Lasiocarpus.