For Viola
Ballard, H.E., Jr. (in prep.). Violaceae of the Southeastern United States.
Ballard, H.E., Jr. 1992. Systematics of the Viola Section Viola in North America north of Mexico. M.S. thesis, Central Mich. Univ., Mount Pleasant.
Ballard, H.E., Jr. 1994. Violets of Michigan. The Michigan Botanist 33: 131-199.
Ballard, H.E., Jr., and D.E. Wujek. 1994. Evidence for the recognition of Viola appalachiensis Systematic Bot. 19: 523-538.
Ballard, H.E., Jr., J. de Paula-Souza, and G.A. Wahlert. 2014. Violaceae. In Kubitzki, K., ed. 2014. The families and genera of vascular plants, XI. Flowering plants – Eudicots – Malpighiales. Springer, Berlin. 331 pp.
Ballard, H.E., Jr., J.T. Kartesz, and M. Nishino. 2023. A taxonomic treatment of the violets (Violaceae) of the northeastern United States and adjacent Canada. J. Torrey Bot. Club 150(1): 3-266.
Ballard, H.E., Jr., K.J. Sytsma, and R.R. Kowal. 1999. Shrinking the violets: phylogenetic relationships of infrageneric groups in Viola (Violaceae) based on internal transcribed spacer DNA sequences. Systematic Botany 23: 439-458.
Gil-ad, N.L. 1997. Systematics of Viola subsection Boreali-Americanae. Boissiera 53: 1-130.
Gil-ad, N.L. 1998. The micromorphologies of seed coats and petal trichomes of the taxa of Viola subsect. Boreali-Americanae (Violaceae) and their utility in discerning orthospecies from hybrids. Brittonia 50: 91-121.
Haines, A.A. 2001. Eleocharis aestuum (Cyperaceae), a new tidal river shore spikesedge of the eastern United States. Novon 11:45–49.
Little, R.J., and L.E. McKinney. 2015b. Viola. In Flora of North America Editorial Committee. 2015. Flora of North America north of Mexico. Volume 6, Magnoliophyta: Cucurbitaceae to Droseraceae. Oxford Univ. Press, New York, NY. 468 pp.
Marcussen, T., H.E. Ballard, J. Danihelka, A.R. Flores, M.V. Nicola, and J.M. Watson. 2022. A revised phylogenetic classification for Viola (Violaceae). Plants 11: 2224. https://doi.org/10.3390/plants11172224
McKinney, L.E. 1992. A taxonomic revision of the acaulescent blue violets (Viola) of North America. Sida Bot. Misc. 7: 1-60.
McKinney, L.E., and N.H. Russell. 2002. Violaceae of the southeastern United States. Castanea 67: 369-379.
Russell, N.H. 1954. Three field studies of hybridization in the stemless white violets. Amer. J. Bot. 41: 679-686.
Russell, N.H. 1955. The taxonomy of the North American acaulescent white violets. Amer. Midl. Nat. 54: 481-494.
Russell, N.H. 1965. Violets (Viola) of central and eastern United States: an introductory survey. Sida 2: 1-113.
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