RESUMO
A molecular phylogeny of Planaltina, including the three previously described species and an undescribed species, is presented. The monophyly of the genus, included in Diapomini, is strongly supported. Its sister group, the remaining Diapomini, includes only species without modified caudal-fin squamation in the present analysis (species of Diapoma with caudal organs were not sampled). Creagrutus is sister to Planaltina plus remaining Diapomini instead of Planaltina being sister to Creagrutus plus Diapomini, as a previous analysis had suggested. Species of Planaltina form two clades: P. britskii plus the new species, with low support (< 50%); and P. myersi plus P. glandipedis, with higher support. Planaltina is rediagnosed from all Characidae based on the morphology of the caudal organ, the absence of a humeral spot and the presence of a complete lateral line. Comments on the caudal-fin squamation of Diapoma and Lepidocharax burnsi, on the type-series of L. burnsi and on the geographic distribution of Planaltina and Lepidocharax species are provided. Finally, a formal description of the aforementioned new species and a novel identification key to Planaltina are presented.