E.  Robbrecht, ?Geography of African Rubiaceae with reference to glacial rain forest refuges?, in The biodiversity of African plants: Proceedings XIVth AETFAT congress, L. J. G.  van der Maesen, van der Burgt, X. M., and de Rooy, J. Mvan Medenb, Eds. Netherlands: Kluwer Academic Publishers, 1996, pp. 564-581.