Calabar bean

Physostigma venenosum This exotic poisonous plant, called Calabar bean or doomsday plant by natives, grows in West Africa.

It is a creeping plant up to 6 m long and has 15-cm long fruits. Its seeds are dark brown, kidney-shaped and very similar to ordinary beans, which is why they cause accidents very often. They are extremely poisonous–one seed is enough to kill a person. 
Local people are familiar with the toxic effect of this plant. They used it in the public trials to challenge the innocence of the accused by administering a poison prepared from Calabar bean. Surviving this poisoning was considered a proof of innocence but it was an extremely rare occasion. 

Its medical significance was discovered in 1855, who received some seeds from an African missioner to facilitate his research. Nowadays, the seeds of Physostigma venenosum are used as a source of the valuable alkaloid physostigmin. Its application is limited to ophthalmology and toxicology. It is also effective in cases of diseases of the peripheral nervous system, muscle and bowel diseases but its usage is now limited because of its toxicity.