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A systematic analysis of the Melastomataceae, a pantropical family of about 4200–4500 species in c. 166 genera, and their traditional allies, the Memecylaceae, with c. 430 species in six genera, suggests a phylogeny in which there are two major lineages in the Melastomataceae and a clearly distinct Memecylaceae. Melastomataceae have close affinities with Crypteroniaceae and Lythraceae, while Memecylaceae seem closer to Myrtaceae, all of which were considered as possible outgroups, but sister group relationships in this plexus could not be resolved. Based on an analysis of all morphological and anatomical characters useful for higher level grouping in the Melastomataceae and Memecylaceae a cladistic analysis of the evolutionary relationships of the tribes of the Melastomataceae was performed, employing part of the ingroup as outgroup. Using 7 of the 21 characters scored for all genera, the maximum parsimony program PAUP in an exhaustive search found four 8-step trees with a consistency index of 0.86. Because of the limited number of characters used and the uncertain monophyly of some of the tribes, however, all presented phylogenetic hypotheses are weak. A synapomorphy of the Memecylaceae is the presence of a dorsal terpenoid-producing connective gland, a synapomorphy of the Melastomataceae is the perfectly acrodro-mous leaf venation. Within the Melastomataceae, a basal monophyletic group consists of the Kibessioideae (Prernandra) characterized by fiber tracheids, radially and axially included phloem, and median-parietal placentation (placentas along the mid-veins of the locule walls). A second clade, the Melastomatoideae, with libriform fibers and lacking included phloem, and with axile-basal or axillary placentation, comprises the remainder of Melastomataceae and consists of eight reasonably well differentiated tribes, one of them paleotropical (Astronieae), three pantropical (Sonerileae, Melasto-meae, and Miconieae), and four neotropical (Merianieae, Microlicieae, Rhexieae, and Blakeeae). The Astronieae have several plesiomorphic characters, such as anthers opening by two slits and axile-basal placentation; all other clades have primarily poricidal anthers' and consistently axillary placentas. A new subfamilial and tribal classification based on the analysis includes an annotated list of all currently recognized genera with numbers of species, distribution and important synonyms. Significant features of the classification include: the placement of Pternandra in a subfamily of its own and the dissolution of the Astronioideae; the merger of three neotropical and paleotropical tribal pairs; and the placement of Rhexia in a tribe of its own. Biogeo-graphy, fossil history, and hypothesized phylogeny of the Melastomataceae imply an east Gondwanian origin of the family.