"Viola adunca". Jepson Flora Project: Jepson Interchange. Jepson Herbarium; University of California, Berkeley. 1993. Retrieved 2015-04-23.
ct.gov
"Connecticut's Endangered, Threatened and Special Concern Species 2015". State of Connecticut Department of Energy and Environmental Protection Bureau of Natural Resources. Retrieved 2 January 2017. (Note: This list is newer than the one used by plants.usda.gov and is more up-to-date.)
Klinkenberg, Brian, ed. (2014). "Viola adunca". E-Flora BC: Electronic Atlas of the Plants of British Columbia [eflora.bc.ca]. Lab for Advanced Spatial Analysis, Department of Geography, University of British Columbia, Vancouver. Retrieved 2015-04-23.
usda.gov
plants.sc.egov.usda.gov
USDA, NRCS (n.d.). "Viola adunca". The PLANTS Database (plants.usda.gov). Greensboro, North Carolina: National Plant Data Team. Retrieved 9 December 2017.