Robbrecht E (1983) The African Genus Tricalysia A. Rich. (Rubiaceae). 3. Probletostemon Revived as a Section of Subgenus Tricalysia. Bulletin Du Jardin Botanique National De Belgique 53: 299-320. doi: 10.2307/3667793.
There is no corrections for Tricalysia elliottii var. centrafricana yet.