Systematics of Tibouchina and allies (Melastomataceae: Melastomateae): A new taxonomic classification

Tibouchina (Melastomataceae: Melastomateae) is an exclusively Neotropical genus that currently includes close to 310 species. These were first described or assigned to 16 other genera, a reflection of the complex taxonomic and phylogenetic history of the genus. Previous phylogenetic analyses have shown that the genus is polyphyletic. Here we present an expanded analysis that includes representatives of 28 genera of New World Melastomateae, as well as representatives of Old World Melastomateae and members of the Marcetieae and Microlicieae. Over 300 species were sequenced for nrITS and the plastid spacers accD-psaI and psbK-psbL. We recovered a large clade of Neotropical Melastomateae that contains Tibouchina along with at least 13 other Neotropical genera. Moreover, Tibouchina is not recovered as monophyletic because three mostly Central American and five mostly Andean genera are nested within it, albeit each these genera are recovered as monophyletic. Many of the previously recognized sections of Tibouchina are recovered as monophyletic or paraphyletic providing a basis for a new classification. Tibouchina is here re-circumscribed into four genera that are each monophyletic and easily diagnosable. This results in a narrowly circumscribed Tibouchina and the re-establishment of Pleroma and Chaetogastra, and the description of a new genus, Andesanthus. Pleroma now also includes Itatiaia, Microlepis and Svitramia. Brachyotum is maintained until its relationship to Chaetogastra can be further examined. This new taxonomic arrangement is more informative and convenient than merging eight other genera into Tibouchina. An identification key, descriptions of genera, and lists of taxa with their current generic assignment and necessary nomenclatural novelties are also presented here.