A molecular phylogeny of the pantropical papilionoid legume Aeschynomene supports reinstating the ecologically and morphologically coherent genus Ctenodon

Abstract

The pantropical and morphologically diverse genus <i>Aeschynomene</i> (Leguminosae, Papilionoideae) comprises ca. 180 species, but its monophyly has never been comprehensively addressed in a molecular phylogenetic context of the dalbergioid clade. Here we have assembled the most complete DNA sequence data (nuclear ribosomal ITS/5.8S and the plastid genes <i>trnL</i> intron and protein-coding <i>matK</i>), representatively sampled both in <i>Aeschynomene</i> and the closely related <i>Dalbergia</i> and <i>Machaerium</i>, as well all currently accepted genera from the dalbergioids. The Bayesian and maximum likelihood phylogenetic analyses unequivocally confirm the non-monophyly of <i>Aeschynomene</i>. The pantropically distributed <i>Aeschynomene</i> sect. <i>Aeschynomene</i>, often inhabiting riparian and wetland habitats, is paraphyletic with respect to the mostly African genera <i>Bryaspis</i>, <i>Cyclocarpa</i>, <i>Geissaspis</i>, <i>Humularia</i>, <i>Kotschya</i>, and <i>Smithia</i>, as well as the South American monotypic genus <i>Soemmeringia</i>. The strongly supported and morphologically coherent clade comprising the American species traditionally classified within <i>Aeschynomene</i> sect. <i>Ochopodium</i>, with a greater ecological predilection for neotropical fire-prone savannas and the seasonally dry tropical forests and woodlands, is here elevated to generic rank. As such, this lineage is re-established as the previously monotypic genus <i>Ctenodon</i>. A complete description of <i>Ctenodon</i> and 78 new combinations for the American species and associated infraspecific taxa are provided, as well as 24 lectotypifications.