Elliptio is thought to be the most speciose genus of Unionids. Early taxonomists described hundreds of taxa and despite once being synonymized to 13 species, there currently are upwards of 38 recognized species. With the advent of molecular techniques, there have been many attempts to resolve this troubled nomenclature and to better understand the evolutionary relationships of both Elliptio and Unionid taxa as a whole. This study utilized 311 sequences of mtDNA gene regions COI and ND1, representing 27 currently recognized species of 25 river basins. Both Bayesian inference and maximum likelihood analyses indicate polyphyly on a genus and species level. Haplotype reconstructions of currently recognized species of the Elliptio sensu stricto failed to uphold the current nomenclature in this group. Haplotypes were shared between numerous species and basins across vast distances. Although a conclusion cannot be reached as to how nomenclature can be improved based upon this study, it reveals new avenues of investigation in order to do so. In conjunction with a better life history understanding, the use of more recent molecular techniques may help elucidate the evolutionary relationships of this group
