The family Icacinaceae is represented in Mexico by four genera of trees (Calatola, Oecopetalum, Mappia, and Ottoschulzia), of which only Calatola is dioecious. Calatola is a Neotropical genus previously considered to consist of about six species, of which two (C. mollis Standl. and C. laevigata Standl.) were reported for Mexico, where the genus occurs in lowland rain forest and middle elevation cloud forest. A unique feature of Calatola is the presence in all parts of the plant of a compund, identified as a flavonoid in the present study, that oxidizes to a blue-violet color upon exposure to air. The present revision, which incorporates data from traditional morphology, field characters, chromosome numbers, pollen, germination and seedling morphology, recognizes five species for Mexico, adding C. costaricensis Standl. and two undescribed taxa to those previously known. C. laevigata is shown to be a rare species of the Pacific slope, while populations of the Mexican Gulf slope, Guatemala, and Belice previously referred to this taxon represent an undescribed species. C. costaricensis displays geographic variation and possible intergradation with C. mollis and thus requires further study. The chromosome counts of n = 14 from two species (and n = ca. 14 from two others) represent the first counts for the genus, first counts for the family in the New World, and a new number for the family. Seed germination occurs in ca. 7-9 month in situ and over 12 months ex situ. All species in Mexico are represented by either small or very dispersed populations and are thus of conservation concern.

Key words: Calatola, Icacinaceae, Mexico