1. Christison R (1855) On the properties of the ordeal-bean of Old Calabar, West Africa. Monthly J Med, 20 (3rd series, 11): 193–204 [for a somewhat abridged presentation of this article, see (Christison 1854–1855)]
2. Dalziel JM (1948) The useful plants of West Tropical Africa. The Crown Agents for the Colonies, 4.Millbank,Westminster, London, S.W.1 – under the authority of the Secretary of State for the Colonies, 256 [an appendix to the 1st edition of (Hutchinson and Dalziel 1958)]
3. Hesse O (1878) Ueber phytosterin und cholesterins. Liebig’s Ann Chem 192:175–179
4. Irvine FR (1961) Woody plants of Ghana with special reference to their uses. Oxford University Press, London, pp 402–404, 792
5. Julian PL (1936) Observations quoted in (anon 1999, Witkop B 1998)