For Rhinotropis
Abbott, J.R. 2011. Notes on the disintegration of Polygala (Polygalaceae), with four new genera for the flora of North America. J. Bot. Res. Inst. Texas 5: 125-137.
Abbott, J.R. 2021. Polygalaceae. In Flora of North America Editorial Committee. 2021. Flora of North America north of Mexico. Volume 10, Magnoliophyta: Proteaceae to Elaeagnaceae. Oxford Univ. Press, New York, NY. 456 pp.
Wendt, T. 1979. Notes on the genus Polygala in the United States and Mexico. J. Arnold Arb. 60: 504-514.