''Physostigma venenosum'', the Calabar bean or ordeal bean, is a

leguminous A legume () is a plant in the family Fabaceae (or Leguminosae), or the fruit or seed of such a plant. When used as a dry grain, the seed is also called a pulse. Legumes are grown agriculturally, primarily for human consumption, for livestock for ...

plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclud ...

Endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

to tropical

Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...

, with a seed poisonous to humans. It derives the first part of its scientific name from a curious beak-like appendage at the end of the stigma, in the centre of the flower; this appendage, though solid, was supposed to be hollow (hence the name from , a bladder, and stigma).

Growth

The plant is a large,

herbaceous Herbaceous plants are vascular plants that have no persistent woody stems above ground. This broad category of plants includes many perennials, and nearly all annuals and biennials. Definitions of "herb" and "herbaceous" The fourth edition of t ...

, climbing

perennial A perennial plant or simply perennial is a plant that lives more than two years. The term ('' per-'' + '' -ennial'', "through the years") is often used to differentiate a plant from shorter-lived annuals and biennials. The term is also wide ...

, with the stem woody at the base, up to in diameter; it has a habit like the

scarlet runner ''Phaseolus coccineus'', known as runner bean, scarlet runner bean, or multiflora bean, is a plant in the legume family, Fabaceae. Another common name is butter bean, which, however, can also refer to the lima bean, a different species. It is ...

, and attains a height of about . The flowers, appearing in axillary peduncles, are large, about long, grouped in pendulous, fascicled

raceme A raceme ( or ) or racemoid is an unbranched, indeterminate type of inflorescence bearing flowers having short floral stalks along the shoots that bear the flowers. The oldest flowers grow close to the base and new flowers are produced as the s ...

s pale-pink or purplish, and heavily veined. The seed pods, which contain two or three seeds or beans, are in length; and the beans are about the size of an ordinary

horse bean ''Vicia faba'', commonly known as the broad bean, fava bean, or faba bean, is a species of vetch, a flowering plant in the pea and bean family Fabaceae. It is widely cultivated as a crop for human consumption, and also as a cover crop. Variet ...

but less flattened, with a deep chocolate-brown color.

Toxicology

Calabar bean contains

physostigmine Physostigmine (also known as eserine from ''éséré'', the West African name for the Calabar bean) is a highly toxic parasympathomimetic alkaloid, specifically, a reversible cholinesterase inhibitor. It occurs naturally in the Calabar bean and ...

, a reversible

cholinesterase inhibitor Cholinesterase inhibitors (ChEIs), also known as anti-cholinesterase, are chemicals that prevent the breakdown of the neurotransmitter acetylcholine or butyrylcholine. This increases the amount of the acetylcholine or butyrylcholine in the syn ...

alkaloid Alkaloids are a class of basic, naturally occurring organic compounds that contain at least one nitrogen atom. This group also includes some related compounds with neutral and even weakly acidic properties. Some synthetic compounds of similar ...

. The alkaloid physostigmine acts in effect like

nerve gas Nerve agents, sometimes also called nerve gases, are a class of organic chemicals that disrupt the mechanisms by which nerves transfer messages to organs. The disruption is caused by the blocking of acetylcholinesterase (AChE), an enzyme that ...

, influencing communication between the nerves and muscles, and resulting in copious salivation, seizures, loss of control over the bladder and bowels, and eventually loss of control over the respiratory system, causing death by asphyxiation. The main antidote to Calabar bean poisoning is the slightly less toxic

tropane alkaloid Tropane alkaloids are a class of bicyclic .2.1alkaloids and secondary metabolites that contain a tropane ring in their chemical structure. Tropane alkaloids occur naturally in many members of the plant family Solanaceae. Certain tropane alkal ...

atropine Atropine is a tropane alkaloid and anticholinergic medication used to treat certain types of nerve agent and pesticide poisonings as well as some types of slow heart rate, and to decrease saliva production during surgery. It is typically given i ...

, which may often succeed; and the other measures are those usually employed to stimulate the circulation and respiration. Unfortunately, the antagonism between

and

is not perfect, and Sir

Thomas Richard Fraser Sir Thomas Richard Fraser (5 February 1841 – 4 January 1920) was a British physician and pharmacologist. Together with Alexander Crum Brown he discovered the relationship between physiological activity and chemical constitution of the body. ...

demonstrated that sometimes the action of the two drugs is summated and death results sooner than from either alone: namely, atropine will save life if three and a half times the fatal dose of physostigmine has been taken, but will hasten the end if four or more times the fatal dose has been ingested.

Historical uses

The people of Old

Calabar Calabar (also referred to as Callabar, Calabari, Calbari and Kalabar) is the capital city of Cross River State, Nigeria. It was originally named Akwa Akpa, in the Efik language. The city is adjacent to the Calabar and Great Kwa rivers and cre ...

used Calabar beans or 'E-ser-e' as an

ordeal poison Trial by ordeal was an ancient judicial practice by which the guilt or innocence of the accused was determined by subjecting them to a painful, or at least an unpleasant, usually dangerous experience. In medieval Europe, like trial by combat, tri ...

, and administered them to persons accused of

witchcraft Witchcraft traditionally means the use of magic or supernatural powers to harm others. A practitioner is a witch. In medieval and early modern Europe, where the term originated, accused witches were usually women who were believed to have us ...

or other crimes. It was considered to affect only the guilty; if a person accused of a crime ingested the beans without dying, they were considered innocent. A form of dueling with the seeds was also practiced, in which the two opponents divide a bean, each eating one half; that quantity has been known to kill both adversaries. Although thus highly poisonous, the bean has nothing in external aspect, taste or smell to distinguish it from any harmless leguminous seed, and disastrous effects have resulted from its being incautiously left in the way of children. The beans were first introduced into

Britain Britain most often refers to: * The United Kingdom, a sovereign state in Europe comprising the island of Great Britain, the north-eastern part of the island of Ireland and many smaller islands * Great Britain, the largest island in the United King ...

in the year 1840; but the plant was not accurately described until 1861, and its physiological effects were investigated in 1863 by Sir

. The bean usually contains a little more than 1% of

s. Two of these have been identified, one called

calabarine ''Physostigma venenosum'', the Calabar bean or ordeal bean, is a leguminous plant, Endemic to tropical Africa, with a seed poisonous to humans. It derives the first part of its scientific name from a curious beak-like appendage at the end of the ...

with

-like effects, and the other, the drug

(with the opposite effect), used in the treatment of

glaucoma Glaucoma is a group of eye diseases that result in damage to the optic nerve (or retina) and cause vision loss. The most common type is open-angle (wide angle, chronic simple) glaucoma, in which the drainage angle for fluid within the eye rem ...

anticholinergic syndrome Anticholinergics (anticholinergic agents) are substances that block the action of the neurotransmitter called acetylcholine (ACh) at synapses in the central and peripheral nervous system. These agents inhibit the parasympathetic nervous system ...

myasthenia gravis Myasthenia gravis (MG) is a long-term neuromuscular junction disease that leads to varying degrees of skeletal muscle weakness. The most commonly affected muscles are those of the eyes, face, and swallowing. It can result in double vision, dro ...

and

delayed gastric emptying Gastroparesis (gastro- from Ancient Greek γαστήρ – gaster, "stomach"; and -paresis, πάρεσις – "partial paralysis"), also called delayed gastric emptying, is a medical disorder consisting of weak muscular contractions (peristalsis) ...

References

* This source includes pharmacological instructions, which are now presumably archaic. * "The killer bean of Calabar",

Laura Spinney Laura Spinney (born August 1971) is a British science journalist, novelist, and non-fiction writer whose 2017 book ''Pale Rider'' is an account of the 1918 influenza pandemic. Education Spinney graduated with a Bachelor of Science degree in N ...

, Histories,
New Scientist
', 28 June 2003. * "A Modern Herbal", Maude Grieve (1931)

{{Taxonbar, from=Q1721924 Medicinal plants of Africa Phaseoleae Taxa named by John Hutton Balfour

Growth

Toxicology

Historical uses

See also

References