Phylogenetic analyses based on five DNA plastid sequences from representative taxa of the Neotropical woody bamboo subtribe Guaduinae were performed to determine the generic limits of Olmeca and the relationships among its species. The phylogenetic position of a putative new taxon from Mexico was also determined. It appeared that, additional to the two species recognized in Olmeca, two Mesoamerican species of Aulonemia-A. clarkiae and A. fulgor-should be transferred to Olmeca. This transfer is supported by morphology. Individuals of an undescribed taxon from the Isthmus of Tehuantepec, Mexico, were also retrieved embedded in the Olmeca group and are newly described as O. zapotecorum. The distribution range of the redefined genus Olmeca, currently composed of five species, now extends from southern Mexico to Honduras.