Physostigma

Physostigma venenosum - Köhler–s Medizinal-Pflanzen-237

Physostigma venenosum is a perennial climbing shrub of the family Fabaceae, native to tropical West Africa. It is known for producing the bean from which the drug physostigmine, also known as eserine, is extracted. Physostigma venenosum is commonly referred to as the Calabar bean, or ordeal bean, due to its use in traditional African medicine and rituals, particularly as a test for witchcraft.

Description

Physostigma venenosum grows as a vine with a thick, woody stem that can reach lengths of up to 50 feet. It has large, alternate, pinnate leaves that are up to 30 cm long, with each leaflet being lanceolate and finely pointed. The plant produces clusters of purple flowers, which are followed by oblong pods containing two to three seeds. The seeds, or beans, are reddish to brown in color, about 1-2 cm in length, and are the source of physostigmine.

Habitat and Distribution

This species is indigenous to the moist forest regions of West Africa, particularly in Nigeria and Cameroon. It thrives in the understorey of tropical rainforests, where it can climb on other vegetation to reach sunlight.

Pharmacological Uses

Physostigmine, extracted from the seeds of Physostigma venenosum, is a potent cholinesterase inhibitor that enhances the levels of acetylcholine, a neurotransmitter, in the nervous system. This action makes it useful in the treatment of various conditions, including glaucoma, Alzheimer's disease, and myasthenia gravis. It has also been used as an antidote for anticholinergic poisoning.

Toxicity

The seeds of Physostigma venenosum are highly toxic and can be lethal if ingested in sufficient quantities. The primary toxic component, physostigmine, acts by inhibiting acetylcholinesterase, leading to an accumulation of acetylcholine in the nervous system. Symptoms of poisoning include salivation, sweating, nausea, vomiting, diarrhea, abdominal pain, visual disturbances, bradycardia, convulsions, and, in severe cases, death due to respiratory failure.

Cultural Significance

In traditional societies in West Africa, the Calabar bean was used as an ordeal poison to determine guilt in accused individuals. It was believed that if a person survived after ingesting the bean, they were innocent, while death indicated guilt. This practice highlighted the bean's significance in judicial and ritual contexts.

Conservation Status

The conservation status of Physostigma venenosum has not been extensively studied, but it is not currently listed as endangered. However, habitat destruction and overharvesting for medicinal purposes could pose threats to its wild populations.

See Also

• Fabaceae
• Cholinesterase inhibitor
• Acetylcholine
• Medicinal plants