Name: Calabar Bean (Physostigma Venenosum)
Otherwise known as: Ordeal Nut, Chopnut
Habitat: The plant is a climbing perennial member of the Leguminoseae family growing up to 15m in rich, moist soil in tropical coastal regions and native to West Africa. It has pinnately trifoliate leaves and produces flowers very similar to the popular European Runner Bean in pendulos racemes of flowers that transform into the large pod which contains three chocolate-coloured beans that are fatal to mammals.
What does it do: Calabar contains a number of toxic alkaloids such as phytostigmine, calabarine, eseridine and eseramine. The plant came to prominence when the British colonised that part of Africa called the Calabar Coast, now modern Nigeria. The district officers discovered the bean was used as the African equivalent of the medieval ‘Ducking Stool’. Those accused of witchcraft or accused of crime were forced to consume the bean and if they vomited it up within the allotted time they were deemed innocent, if they succumbed, they were guilty – few survived.
The British strongly disapproved and viewed the practice as barbaric and outlawed it, particularly as the tribes forced captured white settlers to pursue the same custom, with similar results. However, we are informed the practice continues in rural areas.
Galenus, father of surgery, and physician to Marcus Aurelius, knew of the bean and some Greek herbalists used it to treat chronic constipation, epilepsy and cholera, with varied results.
Physostigmine is known to prolong neurotransmitters, dilate blood vessels and slow the heartbeat. It has become popular in the treatment of cases of Myasthenia Gravis, a rare auto-immune disease, and spastic colon. There has been some experimentation with the alkaloid to depress the effect of spinal chord tetanus. It is used by eye surgeons to treat glaucoma and corneal ulcers.
It was rumoured that a chemical weapon was manufactured from the bean and featured in the Middle-East wars.
Alexander McCowan is author of The World’s most Dangerous Plants