A densely sampled molecular phylogeny of Tachigali (Leguminosae), an evolutionarily successful lineage of neotropical ant-housing canopy trees

Despite recent advances in revealing the evolutionary history of speciose tropical plant clades, many species radiations are still poorly understood phylogenetically. One of these is the species-rich neotropical genus Tachigali (~ 90 spp.), a caesalpinioid legume lineage of mostly ant-housing canopy trees that has diversified in the tropical rainforest biome across the Andean foothills, Amazon basin, and Atlantic Coastal Forest of Brazil. It is also ecologically dominant across the fire-prone savanna vegetation of the Brazilian Cerrado. The taxonomic history of Tachigali has long been confounded with the genus Sclerolobium, with the two differing in floral symmetry. Here, we reconstruct the phylogeny of Tachigali using densely sampled Bayesian and maximum likelihood analyses of nuclear ribosomal (ITS/5.8S) and plastid (matK and trnL intron) DNA sequences for 67 species. All phylogenetic analyses support Tachigali as monophyletic. We recognize a broad circumscription of Tachigali encompassing species exhibiting both radially and bilaterally symmetrical flowers, and we suggest that the traditional generic concept of Sclerolobium should be abandoned. The poor resolution in the Tachigali phylogeny is suggestive of rapid diversification, which has been observed in other species-rich rainforest-inhabiting plant clades across the Neotropics.