1997 IUCN red list of threatened plants (1997)

Checklist of CITES Species (1998)

Checklist of CITES Species: a reference to the appendices to the Convention on International Trade in Endangered Species of Wild Fauna and Flora (1996)

Succulent plants in trade from the wild: analysis of conservation status and international trade - Gillett, Harriet J. (UK Dept of the Environment, Transport and Regions, 1999)