Studies have shown that the genus Acacia Miller s. l. is polyphyletic, consisting of at least seven distinct groups of species. One of these major groups, Senegalia s. l., was also determined to be non-monophyletic. This has resulted in the recent recognition of two new genera, Parasenegalia Seigler and Ebinger, consisting of seven species, and Pseudosenegalia Seigler and Ebinger, consisting of two species. A molecular phylogenetic analysis of these genera and sister taxa, especially Mariosousa Seigler and Ebinger, determined that each is monophyletic, although Parasenegalia visco (Lorentz andGrisebach) Seigler and Ebinger is weakly supported as sister to the rest of Parasenegalia. Pseudosenegalia is sister to the rest of the ingroup, however the node containing Parasenegalia, Mariosousa, and the remaining ingroup grade of Ingeae and Acacia s. s. is poorly supported. These results provide a phylogenetic resolution for the major genera of the American species of Acacia s. l., but full phylogenetic resolution requires a subfamily-based investigation. Simple synapomorphies do not correlate with all genera and these traits are discussed in the context of the phylogeny. A key to the four genera is presented.