Original meiotic chromosome counts are reported for 35 species and one natural interspecific hybrid in 11 genera of Mexican Melastomataceae. These include first counts for 24 species in three of the nine recognized New World tribes in the family. Counts of n = 18 for Arthrostemma parvifolium and n = 36 for Topobea calycularis represent new numbers for these genera. Other counts for species of Arthrostemma (n = 30), Centradenia (n = 18), Clidemia (n = 17, 23), Conostegia (n = 17), Heterocentron (n = 18), Leandra (n = 17), Miconia (n = 17), Monochaetum (n = 18), Pterolepis (n = 7), and Tibouchina (n = 9, 18) corroborate previously reported numbers for these genera. Centradenia, Heterocentron, and Monochaetum with n = 18 and Conostegia with n = 17 appear to have remarkably constant chromosome numbers, whereas Tibouchina exhibits a polyploid series based on x = 9. Clidemia, Leandra, and Miconia, the largest genera of Miconieae, show greatest variation in chromosome numbers. The widespread occurrence of n = 17 suggests that this is the base number in the Miconieae. Two hypotheses are presented to explain the origin of x = 17 in the Miconieae. One suggests straight autotetraploidization of x = 9 followed by chromosome loss (2x 1). The allotetraploid hypothesis proposes that x = 17 is of dibasic origin and may have formed by ancient hybridization of species with 7 and 10 or 8 and 9 haploid chromosomes. The Melastomataceae, a largely tropical family of dicots comprising 185-190 genera and approximately 5000 species, are the largest of the 13 core families in the Myrtales (Dahlgren and Thorne 1984). Unlike the Myrtaceae, the only other family in the order with over 3000 species, the Melastomataceae have been poorly known cytologically. As of 1967, a summary of published chromosome data for the melastomes listed numbers for 24 genera and 56 species (Bolkhovskikh et al. 1969). Only 10 of the numbers enumerated in that summary pertained to New World species. Subsequent papers containing chromosome information about New World melastomes consisted of scattered reports for selected species of Centradenia G. Don (Almeda 1977), Mecranium J. D. Hooker (Nevling 1969), Miconia Ruiz & Pavon (Nevling 1969), Monochaetum (DC.) Naudin (Almeda 1978), Pilocosta Almeda & Whiffin (Almeda and Whiffin 1981), Rhexia L. (Kral and Bostick 1969), Rhynchanthera DC. (Davidse 1970), and Tibouchina Aublet (Favarger 1962; Gadella et al. 1969). In a major review of chromosome cytology in the angiosperms, Raven (1975) included the Melastomataceae in his enumeration of the 16 families in greatest need of additional study. Since then, the number of neotropical melastome species for which there is basic chromosome information has increased considerably so that species belonging to 53 of the 107 New World genera have now been subjected to some kind of preliminary study. Much of this new information was presented by Solt and Wurdack (1980) who reported chromosome numbers for 58 genera and 260 species. In this study we provide 59 meiotic counts for selected species of Melastomataceae from Mexico. Chromosome numbers have heretofore been reported for only 11 species in six genera of Mexican melastomes. A geographic emphasis on Mexico represents a convenient starting point in our effort to augment chromosome data for neotropical Melastomataceae. Mexico, with 25 genera and 190 species of Melastomataceae (63 of which are endemic to the country) is the northernmost limit for familial diversity in the western hemisphere.