Physostigma

Physostigma is a genus of flowering plants in the legume family Fabaceae, native to tropical western Africa. The best known member is Physostigma venenosum Benth., commonly called the Calabar bean or esere. The plant is a woody climber or shrub with pinnate leaves and pea-like flowers; the fruit is a pod containing several seeds.

Phytochemistry and uses: The seeds contain the alkaloid physostigmine (eserine), a reversible inhibitor of acetylcholinesterase. Isolation of physostigmine in the 19th century led to medical applications, particularly in ophthalmology where the compound is used to lower intraocular pressure in glaucoma, and as a pharmacological tool in anesthesia settings. Extracts from Physostigma venenosum have also played a notable role in toxicology and pharmacology due to their potent activity.

Distribution and cultivation: Physostigma is native to tropical West Africa. It is not a major agricultural crop but is sometimes cultivated in botanical gardens and specialized plantations for alkaloid production. Cultivation requires careful handling because of the plant’s toxic seeds and other plant parts.

Toxicity and safety: All parts of the plant, especially the seeds, are toxic if ingested. Ingestion can cause vomiting, abdominal pain, dizziness, seizures, and potentially fatal outcomes. Handling seeds and plant material should be done with caution, using appropriate safety practices to prevent accidental exposure or ingestion.

See also: Calabar bean; physostigmine.