The closely related neotropical melastomean genera Pterogastra and Schwackaea are revised, the species illustrated, and their distribution mapped. Schwackaea is maintained as a monotypic genus because it is readily distinguished from all other melastomes by its 8-winged capsule. This weedy little plant occurs from Mexico throughout Central America, chiefly on the Pacific slope, to northern Colombia and on Cocos Island and grows in natural or man-made savannas from sealevel to 2000 m altitude. Two species are recognized in Pterogastra and one new combination, P. divaricata spp. glabra, is made. Pterogastra is characterized by distinctly 4- or 5-winged capsules, unlike those of Schwackaea or any other New World melastome. The more widespread species occurs in Colombia, Venezuela, Guyana, Ecuador, and Peru at altitudes between sealevel and 2600 m in natural or disturbed grasslands. The second species is endemic in southwestern Venezuela and is confined to natural savannas at low altitudes.