Two new species of Cucurbitaceae, tribe Cucurbiteae, with trifoliolate leaves are described from Costa Rica, one each in Cayaponia Silva Manso and Cionosicys Grisebach. Cayaponia hammelii Grayum, with large, pendent staminate flowers, ranges from Costa Rica to Pacific Ecuador, while the exceptionally large-fruited Cionosicys guabubu Grayum & J. A. González is restricted to Nicaragua, Costa Rica, and central Panama. Both of these new species have sometimes been misidentified as Cayaponia granatensis Cogniaux, a species with trilobate leaves that is dubiously present in Mesoamerica. The distinction between Cayaponia and the similar Cionosicys is discussed in some detail, and a key is provided for all species of Cionosicys with validly published names.