The Calabar bean (Physostigma venenosum Balf., 1861) is a herbaceous species belonging to the Fabaceae family.
From a systematic point of view it belongs to:
Species P. venenosum.
The term Physostigma comes from the union of the two words physo, from the Greek φῡσα phýsa bladder, swelling, and from stigma, that is: puncture, stigma, stigmata, mark, sign, stain, from the Greek στίγμα stígma (from στίζω stízo to prick, brand) , it then passed into botany to indicate the apical part of the pistil where there is a pore capable of receiving pollen.
The specific epithet venenosum comes from venénum poison: poisonous, poisoned.
Geographic Distribution and Habitat –
Physostigma venenosum is a plant that grows spontaneously in western Africa, especially in Guinea, along the Calabar river.
Its range is that of western tropical Africa, from Sierra Leone to Gabon and the Democratic Republic of the Congo.
Its natural habitat is that of closed rainforests, primary and secondary, dry and humid; seasonally flooded riparian forest; swamps.
The Calabar bean is a climbing herbaceous perennial plant that can grow up to 15 – 20 meters relatively similar to a large bean.
The stem is woody at the base, up to 5 centimeters in diameter.
The flowers, which appear in axillary peduncles, are large, about 25 mm long, grouped in pendulous racemes, pale pink or purplish fasciculate and strongly veined. The pods, which contain two or three seeds or beans, are 15–18 cm long.
The legume, which ripens in summer, is 15-18 cm long and contains 2-3 large reniform seeds, 2-3 cm long, covered by a bright brown integument. They are odorless, tasteless and very hard.
Physostigma venenosum is a plant that grows both spontaneously in its natural habitat and cultivated.
For its cultivation it requires a minimum temperature of 15 – 18 °C.
For best and fastest growth it requires a sunny position in rich, well-drained soil.
The plant propagates mainly by seed. Sowing should be done when the seeds are perfectly ripe.
Customs and Traditions –
Physostigma venenosum is a leguminous plant, endemic to tropical Africa, whose seeds are poisonous to humans. As mentioned, the first part of its scientific name derives from a curious beak-shaped appendage at the end of the stigma, in the center of the flower; this appendage, although solid, must have been hollow (hence the name from φῦσα, bladder and stigma).
It also has a number of medicinal applications, but is most commonly grown for the alkaloids contained in the seeds which are extracted and used in modern medicine.
The seeds are normally harvested from the wild, although some cultivation is practiced in some areas, particularly in India.
It was once used in Nigeria in a “poison ordeal” in which a suspected criminal had to drink a bean solution: if it killed them they were guilty but if they survived they were innocent. This probably worked to some extent as innocent people were more likely to consume the drink in one gulp and then vomit before too much of the toxin had been absorbed, while guilty people were more likely to sip it slowly and cautiously, thus ensuring that more of the toxins were absorbed.
A form of seed dueling was also practised, in which the two opponents split a bean by each eating half; that amount is known to kill both opponents. Though so highly poisonous, the bean has nothing in external appearance, taste, or smell which distinguishes it from any harmless leguminous seed, and disastrous effects have resulted from its being incautiously left in the way of children. Beans were first introduced to Great Britain in the year 1840; but the plant was not accurately described until 1861, and its physiological effects were studied in 1863 by Sir Thomas Richard Fraser. The bean usually contains just over 1% alkaloids. Two have been identified, one called calabarin, with effects similar to atropine, and the other, physostigmine (with opposite effect), which has been shown to affect the parasympathetic nervous system, used in the treatment of glaucoma, anticholinergic syndrome, of myasthenia gravis and other effects on the body.
In fact, in the medicinal field, even if highly poisonous, the seed has a number of applications.
It is a narcotic herb that depresses the central nervous system, parasympathetic nervous system, contracts the pupil of the eye, increases blood pressure and stimulates peristalsis.
Physostigmine is isolated from the seed and used in eye drops to reduce pressure on the eyeball and, as mentioned, in the treatment of conditions such as glaucoma
It is also prescribed for internal use in the treatment of neuromuscular diseases, especially myasthenia gravis, and for the treatment of postoperative constipation.
It should be noted that physostigmine, a reversible cholinesterase inhibitor alkaloid, actually acts like a nerve gas, affecting the communication between nerves and muscles and causing profuse salivation, seizures, loss of bladder and bowel control, and eventually loss of control over the respiratory system, causing death by asphyxiation.
The primary antidote to Calabar bean poisoning is atropine, a slightly less toxic tropane alkaloid, which can often be successful; the other measures are those usually employed to stimulate circulation and respiration. Unfortunately, the antagonism between physostigmine and atropine is not perfect, and Sir Thomas Richard Fraser has shown that sometimes the action of the two drugs is combined and death results sooner than from either alone: namely, atropine. it will save life if three and a half times the fatal dose of physostigmine has been taken, but hasten the end if four or more times the fatal dose has been ingested.
As far as contraindications in pharmacological use are concerned, its use must be avoided in case of proven hypersensitivity to one or more components of the calabar bean.
Method of Preparation –
The drug of Physostigma venenosum consists of the black seeds.
The whole seed is used in herbal medicine but should only be prescribed by trained practitioners.
It has been used in the treatment of conditions such as tetanus, epilepsy and rheumatism.
Used in excess, it causes muscle weakness, respiratory failure and cardiac arrest.
– Acta Plantarum – Flora of the Italian Regions.
– Wikipedia, the free encyclopedia.
– GBIF, the Global Biodiversity Information Facility.
– Useful Tropical Plants Database.
– Conti F., Abbate G., Alessandrini A., Blasi C. (ed.), 2005. An annotated checklist of the Italian vascular flora, Palombi Editore.
– Pignatti S., 1982. Flora of Italy, Edagricole, Bologna.
– Treben M., 2000. Health from the Lord’s Pharmacy, Advice and experiences with medicinal herbs, Ennsthaler Editore.
Attention: The pharmaceutical applications and alimurgical uses are indicated for informational purposes only, they do not in any way represent a medical prescription; we therefore decline all responsibility for their use for curative, aesthetic or food purposes.