Hidden in the hills: phylogeny of the freshwater mussel genus Alasmidonta (Bivalvia: Unionidae) and description of a new species

Inaccurate taxonomy can lead to species in need of conservation being overlooked, which makes revisionary systematics crucially important for imperilled groups. The freshwater mussel genus Alasmidonta is one such group in need of study. Here, we take a multilocus phylogenetic approach to assess species-level taxonomy of Alasmidonta and test monophyly of this genus. Phylogenetic inference resulted in polyphyly of Alasmidonta. Lasmigona, which was included to test monophyly of Alasmidonta, was also polyphyletic. Species delimitation methods disagreed about whether Alasmidonta arcula, Alasmidonta triangulata and Alasmidonta undulata are distinct species, but all delimitation methods agreed that Alasmidonta harbours an undescribed species that would be considered Alasmidonta varicosa under current taxonomy. Given conflict among species delimitation methods and geographical separation, we maintain the current taxonomy for A. arcula and A. triangulata. The undescribed species is restricted to rivers of the Uwharrie Mountains region in North Carolina, USA that flow into the Pee Dee River from the east and can be distinguished morphologically from A. varciosa by higher and wider placed adductor mussels and a hooked pseudocardinal tooth. We offer insights into how supraspecific taxonomy of subtribe Alasmidontina might be resolved and formally describe the lineage from the Uwharrie Mountains region as Uwharrie elktoe, Alasmidonta uwharriensis sp. nov.