Unifoliolate leaves are relatively rare in the species-rich dalbergioid clade of papilionoid legumes (Leguminosae, Papilionoideae). For the pantropical, diverse genus Aeschynomene (ca. 180 species), the only known record of unifoliolate species described so far is the savanna-inhabiting A. simplicifolia from Chapada dos Veadeiros in Goiás, Brazil. The current work provides a description, illustrations, and a distribution map of another unifoliolate species, Aeschynomene chicocesariana, which was newly discovered in the rupestrian grasslands of Chapada Diamantina in Bahia, Brazil. Bayesian phylogenetic analyses of DNA sequence data (nuclear ribosomal ITS/5.8S and the plastid genes matK and trnL intron) have unequivocally placed A. chicocesariana with the rest of Aeschynomene species that are traditionally placed within Aeschynomene sect. Ochopodium. This result agrees with the shared morphology of A. chicocesariana and members of that section.