­Previous analyses have revealed deep divergences among populations of the relictual and enigmatic rove beetle, Dasycerus carolinensis Horn. New data from additional populations, molecular markers, and morphology unambiguously reveal this 'species' to represent a complex of closely related species, distinguishable by characters of the male genitalia, and corresponding closely to geographically coherent clades discovered by molecular analyses. Calibrated dating analyses show Appalachian Dasycerus to have been diverging in the region for more than 10 million years, yet largely respecting important biogeographic barriers in the region, such as the French Broad and Little Tennessee River drainages. In addition to discussing finer scale biogeographic patterns in the group, we formally recognize 9 new species from within what was formerly known as D. carolinensis: D. virginiensis sp. nov., D. tuckasegee sp. nov., D. pacolet sp. nov., D. chattooga sp. nov., D. itseyi sp. nov., D. unicoi sp. nov., D. nikwasi sp. nov., D. egwanulti sp. nov., and D. gadalutsi sp. nov.. It was not, however, possible to assign all samples to one of these species, and specimens from some sparsely sampled outlying areas, northern Alabama and central Tennessee in particular, may represent additional species. 

The data set comprises sequences from two regions of the mitochondrial COI gene and one of the Carbamoylphosphate synthase domain protein (CAD) gene, generated through PCR-based Sanger and Next-generation sequencing.