For Obolaria
Gillett, J.M. 1959. A revision of Bartonia and Obolaria (Gentianaceae). Rhodora 61: 43-63.
Pringle, J.S. 2023. Gentianaceae. Pp. 3-92 In Flora of North America Editorial Committee. 2023c. Flora of North America north of Mexico. Volume 14, Magnoliophyta: Gentianaceae to Hydroleaceae. Oxford Univ. Press, New York, NY. 505 pp.
Struwe, L., and J.S. Pringle. 2018. Gentianaceae. In Kadereit, J., & V. Bittrich. 2018. The families and genera of flowering plants. XV. Flowering plants. Eudicots. Apiales, Gentianales (except Rubiaceae). Springer, Cham.
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