Template:Ballard, Sytsma & Kowal, 1998
- Ballard, H.E., Jr., Sytsma, K.J., & Kowal, R.R. 1998. Shrinking the violets: Phylogenetic relationships of infrageneric groups in Viola (Violaceae) based on internal transcribed spacer DNA sequences. Systematic Botany 23(4): 439–458. jstor