Phylogenetic relationships inBrachyotumand allies (Melastomataceae, Melastomateae): a reassessment of the limits of the genera

Abstract

In the past decade, several phylogenetic studies based on molecular data have been generated and changed our view on the evolutionary history and classification of Melastomataceae. Nonetheless, given the size of the family, some groups are still under-sampled and poorly understood, such as the clade formed by Brachyotum and allies in Melastomateae, including three genera, Andesanthus, Brachyotum and Chaetogastra. The principal objective of this work was to further test the relationships in this clade by increasing taxon and locus sampling and by including morphological character reconstructions. In this study, we included nuclear (nrITS, nrETS and waxy) and plastid sequences (accD-psaI, psbK-psbL, trnS-trnG) from 129 species and 29 genera of Melastomataceae, corresponding to c. 46.5% of the species belonging to the clade, and that were used to build phylogenetic hypotheses. We also estimated the evolution of 23 morphological characters through ancestral state reconstruction and the elevational ranges of the species. Our results recovered two major clades: (1) Brachyotum, with species traditionally recognized in Brachyotum, but also including a few species traditionally recognized in Tibouchina; and (2) Chaetogastra, with most species traditionally recognized in Tibouchina, mainly from Tibouchina sections Pseudopterolepis, Diotanthera, Simplicicaules and Purpurella. Andesanthus was placed as sister to Brachyotum and allies in previous phylogenetic analyses; however, in this study it has been recovered as sister to the clades formed by Heterocentron and allies, Monochaetum and allies, and Brachyotum and allies. Four morphological characters can be useful to distinguish genera and clades among Brachyotum and allies: habit; flower position; the angle formed by the petals in relation to the hypanthium; and stamen arrangement. We also find that species in the Brachyotum clade occur at higher elevations (1500–4700 m) than Chaetogastra spp. (sea level to c. 3200 m, but more common at lower elevations, c. 600 to 1800 m). Based on all this evidence we propose the maintenance of Brachyotum as a genus segregated from the recently reinstated Chaetogastra. This work is a contribution to the systematics of Melastomateae, with an improvement in the resolution of the trees in relation to previous phylogenetic analyses, indicating that subclades have a strong relationship with geographical distribution.