We used a combination of amplified fragment length polymorphisms (AFLP) and morphological data from 272 individuals from 59 populations to investigate the species-level taxonomy of Carex roanensis and allied species. There were two taxonomic problems in this group: identifying the appropriate taxonomic status for Carex roanensis, and clarifying the distinctions (if any) between C. virescens and C. swanii. Principal coordinate analysis of the morphological data suggested four entities corresponding to C. aestivalis, C. roanensis, C. swanii, and C. virescens, but clear discrimination was not possible. In contrast, the AFLP data showed marked discontinuities among these four species, placing even morphological intermediates into one of four groups. Analysis of molecular variance revealed significant population differentiation within each species, but only C. virescens had any detectable differentiation between geographic regions. This study confirms the species-level distinction between the common and widespread taxa C. swanii and C. virescens, as well as that of the globally rare Appalachian endemic C. roanensis.