In this study we present a phylogenetic analysis of Melastomeae, focusing on the Neotropical members of the tribe, a group of c. 70 species in 30 genera. In total, 236 species, including outgroups (Miconieae and Merianieae) and representatives of the Microlicieae and Rhexieae, were sequenced for the nuclear ribosomal internal transcribed spacer (nrITS), and the plastid spacers accD‐psaI and psbK‐psbL. Melastomeae are not resolved as monophyletic because a group of mostly herbs and small trees with mostly tetramerous flowers (Acanthella, Aciotis, Acisanthera, Appendicularia, Comolia, Ernestia, Fritzschia, Marcetia, Macairea, Nepsera, Sandemania and Siphanthera) is nested between Rhexieae and Microlicieae. The remaining New World Melastomeae are not resolved as monophyletic, because a group of Old World genera (Osbeckia, Melastoma, Tristemma and allied genera) are nested in the tribe. The large genus Tibouchina is not monophyletic because Brachyotum, Bucquetia, Castratella, Centradenia, Chaetolepis, Heterocentron, Itatiaia, Microlepis, Monochaetum, Pilocosta, Svitramia, and Tibouchinopsis are nested in it, even although all of these genera are recovered as monophyletic. Each major clade has remarkable habitat and geographical integrity. The clade formed by Tibouchina and allies appears to have arisen in savannas in lowland South America and later expanded to forest, campo and high Andean biomes. At least two groups have radiated in eastern Brazil, and two other groups in the Andes and mountains of Central America. Niche conservatism and colonization of adjacent environments seem to have driven speciation in Neotropical Melastomeae. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, ●●, ●●–●●.

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.

Poteranthera (Melastomataceae) is a genus of small, annual herbs with narrow leaves, that inhabit humid savannas in South America and are visible only when in bloom. Due to their size and paucity of collections, the phylogenetic position of Poteranthera has been uncertain to this point. Poteranthera has been at times associated, confused, or placed in Acisanthera and/or Siphanthera. Phylogenetic analyses based on DNA sequence data place Poteranthera unequivocally within the Microlicieae and not closely related to Acisanthera or Siphantera. These results are consistent with seed and anther morphology. Putative morphological synapomorphies for this genus are the glandular hairs restricted to the leaf margins and the apically constricted hypanthium. Based on morphology, Acisanthera leptalea seems better placed in Poteranthera and the new combination Poteranthera leptalea is made. An expanded generic description is also provided.

The Marcetia alliance of Melastomataceae is an exclusively Neotropical group that includes at least 12 genera of mostly herbs and subshrubs, occurring in the cerrado of central Brazil and savannas of the Amazon region and Guayana highlands. This study aimed to test the monophyly of genera in the Marcetia alliance, evaluate their phylogenetic relationships and generic boundaries, and investigate morphological characters as potential synapomorphies for delimiting clades or genera. We used nuclear (ITS, ETS) and plastid (accD‐psaI, atpH‐atpF, trnS‐trnG) DNA sequences of 107 terminals in 12 genera from the alliance. Aciotis, Fritzschia, Marcetia and Siphanthera were shown to be monophyletic and supported by molecular and morphological characters. Other genera with variable morphology and wider distributions, such as Acisanthera, Comolia, Ernestia and Macairea, were recovered as paraphyletic or polyphyletic. Most morphological characters analysed were found to be homoplastic, but when combined they are potentially useful for the diagnosis of genera and infrageneric groups. This study represents a major step in understanding internal relationships and provides the basis for a revision of the generic classification in the Marcetia alliance.

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