For Polypremum
Rabeler, R.K. 2019. Polypremum. In Flora of North America Editorial Committee. 2019. Flora of North America north of Mexico. Volume 17, Magnoliophyta: Tetrachondraceae to Orobanchaceae. Oxford Univ. Press, New York, NY. 737 pp.
Rogers, G.K. 1986. The genera of Loganiaceae in the southeastern United States. J. Arnold Arb. 67: 143-185.
Wagstaff In Kadereit, J.W. 2004. The families and genera of vascular plants. VII. Flowering plants – Dicotyledons – Lamiales (except Acanthaceae including Avicenniaceae). Springer, Berlin. 478 pp.