The acaulescent blue violets have been the most problematic group within the genus Viola. Most taxa occur within the eastern half of the United States although several reach their limits of distribution in Canada and one reaches the western coast. Ten species, two subspecies and four varieties are recognized by McKinney on the basis of extensive morphological comparisons in both field and herbaria and a better understanding of historic literature pertinent to the genus. McKinney spent fifteen years conducting field and herbaria studies during which over 25,000 specimens were examined and annotated.

New taxonomic names include: Viola pedatifida ssp. brittoniana ssp. nov.—Viola septemloba ssp. egglestonii ssp. nov.—Viola sororia var. affinis var. nov.—Viola sororia var. missouriensis var. nov.—Viola sororia var. novae-angliae.