Leeuwenberg, A.J.M. & Van Dilst F.J.H. 2001. Series of revisions of Apocynaceae XLIX Carissa L. Backhuys Publishers, Leiden.
http://pza.sanbi.org/references/leeuwenberg-ajm-van-dilst-fjh-2001-series-revisions-apocynaceae-xlix-carissa-l-backhuys