Shimai, H., Kondo, K. (2007). Phylogenetic analysis of Mexican and Central American Pinguicula (Lentibulariaceae) based on internal transcribed spacer (ITS) sequence. Chromosome Botany (2007) 2: 67-77.
Casper, S.J. (1966). Once More: The Orchid-Flowered Butterworts. Brittonia 18(1), 19-28.