Molecular Phylogeny of<i>Stryphnodendron</i>(Mimosoideae, Leguminosae) and Generic Delimitations in the<i>Piptadenia</i>Group

Premise of research. Despite recent progress on the systematics of the Leguminosae, the relationships between some genera, as well as their circumscriptions, remain uncertain. Here we investigate the relationships between Stryphnodendron and closely related genera in the Piptadenia group, a clade of problematic taxonomy for which a robust phylogenetic hypothesis is still lacking.Methodology. Taxonomic sampling included 23 species of Stryphnodendron (77% of the genus) and representatives of genera of the Piptadenia group. DNA (matK/trnK, trnD-trnT, trnL-trnF, and ITS) sequences constituting a data set with 6798 bp and 94 terminals were used in parsimony and Bayesian analyses. A set of 17 morphological characters were optimized on the estimated phylogeny to evaluate clade synapomorphies and character evolution.Pivotal results. Our increased molecular and taxonomic sampling improved the resolution of a previously largely unresolved clade that included Microlobius, Parapiptadenia, Pityrocarpa, Pseudopiptadenia, and Stryphnodendron. Major lineages within this clade are an early-diverging clade containing the sister genera Parapiptadenia and Pseudopiptadenia; the genus Pityrocarpa, with Pseudopiptadenia brenanii nested within it; and a Stryphnodendron clade including the monospecific genus Microlobius. Samples of Stryphnodendron grouped into three strongly supported clades: a group of seven species bearing large leaflets and relatively few pairs of pinnae, sister to Microlobius foetidus; a clade containing samples of Stryphnodendron duckeanum; and a large and poorly resolved clade containing the remaining species of Stryphnodendron, including species with small leaflets and higher number of pinnae and highly specialized dwarf subshrubs adapted to savanna fire regimes. Lack of resolution within this clade suggests rapid and recent diversification in both savannas and rain forests in the Neotropics.Conclusions. Our findings highlight the importance of densely sampled phylogenies to rigorously test the monophyly of genera. Key morphological characters are proposed to assist generic delimitations in the Piptadenia group. New taxonomic rearrangements are needed in order to accommodate the results presented here.