Molecular systematics of the North American freshwater bivalve genus Quadrula (Unionidae: Ambleminae) based on mitochondrial ND1 sequences.

A molecular phylogeny of the bivalve genus Quadrula (Unionidae) was constructed based on nucleotide sequences of the mitochondrial ND1 gene. Phylogenetic analysis of 66 specimens representing 17 of the 20 currently recognized taxa within Quadrula, three closely allied species, and 16 outgroup taxa reveals a non-monophyletic Quadrula due to the placement of Tritogonia verrucosa, 'Fusconaia' succissa, and 'Quincuncina' infucata. We suggest that the taxonomic description of the genus Quadrula be expanded to include these species. Within the genus, we continue to recognize three monophyletic species groups (the quadrula, metanvera, and pustulosa species groups), as historically described; however, the pustulosa species group must include 'F.' succissa and 'Quincuncina' infucata. Finally, while our findings place the monotypic genus Tritogonia within Quadrula, its relationship to members within the genus Quadrula remains unresolved.