Acokanthera venenata is a shrub used as the source of an arrow poison and to coat caltrops. All three plants of the genus Acokanthera contain toxic cardiac glycosides strong enough to cause death. This plant and other species of the genus are found in South Africa and Abyssinia. It was previously also known as Toxicophlaea Thunbergii.
Acokanthera schimperi is employed for the same purpose.
References
http://www.factopia.com/gardening-vol4/toxicophlaea.htm Factopia, Toxicophlaea