The number of naturally occurring taxa of Vitis reported for North Carolina has ranged from five to nine, with seven being recognized in this treatment. Widespread natural hybridization was believed earlier to be responsible for this discrepancy; however, clinal variation was determined to be a complicating factor in the systematics of Vitis, and accounts for substantial morphological differences within species. Clines exist in two of North Carolina’s grapes, V. aestivalis and V. cinerea. Pubescent V. aestivalis var. aestivalis of the Coastal Plain and Piedmont gradually becomes more glabrous and more glaucous on the abaxial leaf surfaces with increasing elevation. Mountain forms are treated as V. aestivalis var. argentifolia. Vitis cinerea has a similar clinal variation with leaves becoming more glabrous with elevational increase. Relatively glabrous plants of the Piedmont and mountains are V. cinerea var. baileyana and pubescent plants of the Coastal Plain are V. cinerea var. floridana. The morphology of V. vulpina, V. labrusca, and V. rotundifolia remains constant throughout the state. Differences in phenology and ecological preference are believed to promote reproductive isolation within subgenus Vitis. Barriers are not completely effective, however, since five putative hybrids were located in natural populations.