References
For Hexasepalum
Bacigalupo, N.M., and E.L. Cabral. 1999. Revisión de las especies americanas del género Diodia (Rubiaceae, Spermacoceae). Darwiniana 37: 153-165. Google Scholar
Cabaña Fader, A.A., E. Bezerra de Souza, E.K. de Sousa Brandão, and E.L. Cabral. 2019. Hexasepalum nordestinum (Rubiaceae): A new species from two disjoint and fragmented areas in northeast Brazil, with a key to the American species of the genus. Syst. Bot. 44: 203-209. Google Scholar
Kirkbride, J.H., Jr., and P.G. Delprete. 2015. New combinations in Hexasepalum (Rubiaceae: Spermacoceae). J. Bot Res. Inst. Texas 9: 103-106. Google Scholar
Rogers, G.K. 2005. The genera of Rubiaceae in the southeastern United States, part II. Subfamily Rubioideae, and subfamily Cinchonoideae revisited (Chiococca, Erithalis, and Guettarda). Harvard Papers in Botany 10: 1-45. Google Scholar