Prota 11(1): Medicinal plants/Plantes médicinales 1
Bol. Soc. Afr. Italia 10(11–12): 12 (1891).
Carissa schimperi A.DC. (1844), Acokanthera ouabaio Poisson (1888).
Common poison bush, arrow-poison tree (En). Msunguti, msungu (Sw).
Origin and geographic distribution
Acokanthera schimperi occurs from Eritrea south to Tanzania and west to Uganda, Rwanda and eastern DR Congo. It is also found in southern Yemen.
Acokanthera species are among the most commonly used plant species for the preparation of poison in East Africa. It is either used on its own or mixed with other plant or animal parts. The bark, wood and roots are the usual ingredients for arrow poison, and they are also used for suicide and homicide. The only treatment against the poison is immediate excision of the flesh around the wound, or sucking the blood from the wound. The poison is also used in killing wild animals and stray dogs from fields and homes.
In Ethiopia the leaves and bark are applied to the skin to treat skin disorders, and an infusion of the leaves is gargled to treat tonsillitis. Dried pulverized leaves with honey are taken as an antifertility medicine. In Kenya Samburu women drink a bark decoction when their menstruation does not stop. In Kenya and Tanzania a hot infusion of the pounded root is drunk in small quantities to treat sexually transmitted diseases, and also as an aphrodisiac. In Uganda a leaf decoction is given to cattle that have a cold. A mixture made from the leaves, bark and butter is used for gall-bladder problems. The smoke of dried roots and twigs is insect repellent; too much smoke is harmful for humans as well.
The fruits are edible and an important famine food. They are sweet and slightly bitter when fully ripe. They are also used to make jams. The unripe fruits and seeds are highly poisonous, and several cases of accidental poisoning of children have been recorded. The latex in the fruits is used as chewing gum by children. The wood is very hard and compact and branches are used in making spear shafts. In Uganda, it is used as firewood and to make charcoal. Acokanthera schimperi serves as an ornamental, shade or live fence tree in parks or around houses.
Production and international trade
The stem bark and roots of Acokanthera schimperi are locally traded for poison production. The ready-made poison is also sold in East Africa. There are no data on traded volumes and value.
All plant parts of Acokanthera schimperi, except the pulp of the ripe fruit, contain large amounts of cardiac glycosides (cardenolides), of which nearly 20 have been identified. The glycosides are responsible for the activity as arrow poison, but also act as cardiac stimulant. The main compounds are acovenoside A (0.3–1.8%), with acovenosigenin as aglycone, followed by ouabain (0.1–5%) with ouabagenin as aglycone, and traces of acolongifloroside K. Acokanthera schimperi plants from the Nairobi region in Kenya contain the highest amounts of acovenoside A, and lowest amounts of ouabain. Plants from the coastal region of Kenya contain mainly ouabain, while plants from Eritrea contain only half as much acovenoside A as those from Nairobi, but much more ouabain. Minor components also vary with origin and may include acoschimperosides N, P, Q and V. The main differences with Acokanthera oppositifolia (Lam.) Codd are the higher amounts of ouabain and the lower amounts of acolongifloroside K, but both species are equally poisonous. Ouabain and acolongifloroside K are the most cardioactive compounds; they are highly toxic and can cause death even in minute doses. The other compounds are slightly less toxic. Cardiac glycosides are given in low doses to patients suffering from congestive heart failure. In higher doses, they have a direct inhibiting action on the atrioventricular conduction together with a decrease of the heart rate. Injection of the arrow poison into an animal causes death almost immediately, while humans inflicted with an arrow wound die in 30 minutes to 2 hours. In medicine, ouabain is used as a remedy for congestive heart failure, like glycosides from Digitalis.
A methanol extract from the leaves showed significant antiviral activity against influenza virus A, coxsackievirus B3 and HSV-1 by inhibiting their replication. The extract also exhibited significant antibacterial activity against Staphylococcus aureus and Pseudomonas aeruginosa, and significant antifungal activity against Trichophyton mentagrophytes.
Adulterations and substitutes
Poison from Acokanthera oppositifolia (Lam.) Codd may be used as a substitute for that of Acokanthera schimperi, although the latter species is more widely used for poison production. Dishonest dealers sometimes adulterate the poison with black earth.
Much-branched, evergreen tree, sometimes a shrub, up to 9(–10) m tall, with short trunk; bark brown, soft; crown dense, rounded; young branches glabrous or hairy, conspicuously angled and ribbed. Leaves decussately opposite, simple and entire; stipules absent; petiole 1–6(–9) mm long; blade elliptical to ovate or broadly ovate, 2–10 cm × 1.5–6.5 cm, base cuneate or rounded, apex acute, obtuse or rounded, with hard mucro, leathery, glossy, glabrous or shortly hairy, pinnately veined, lateral veins obscure, with looping connections. Inflorescence a dense axillary cyme, many-flowered. Flowers bisexual, regular, 5-merous, fragrant; sepals free, ovate to lanceolate, (1–)1.5–2.5 mm long, apex acuminate to acute, shortly hairy or glabrous outside, ciliate; corolla tube cylindrical, 8–12.5 mm long, glabrous or shortly hairy outside, inside sparsely hairy in the upper half and wrinkled below, pink or red, lobes ovate, 2.5–5 mm long, apex acute, glabrous above, glabrous to shortly hairy below, ciliate, white; stamens inserted at 7–10 mm from the base of the corolla tube, slightly exserted; ovary superior, ellipsoid, 2-celled, style slender, 7–10 mm long, stigma minutely bifid. Fruit an ellipsoid berry 1–2.5 cm long, purple when ripe, pulp green to deep red, 1–2-seeded. Seeds ellipsoid, plano-convex, 6–13 mm long, smooth, glabrous.
Other botanical information
Acokanthera comprises 5 species and is restricted to Africa, although Acokanthera schimperi is also found in Yemen. The genus is related to Carissa. There are two types of Acokanthera schimperi: a large-leaved (up to 11 cm) and a small-leaved one. A third type that is climbing and has shortly and sharply recurved leaf margins has been reported in Kenya. Acokanthera schimperi has been domesticated in coastal Kenya by the Giriama people. The domestication process has increased the genetic variability of the species; the large-leaved, possibly domesticated types have very high amounts of ouabain.
The stem bark of Acokanthera laevigata Kupicha from Tanzania and Malawi, also called ‘msunguti’ in Swahili, is widely used to make arrow poison. It contains similar alkaloids as the other Acokanthera species. The tough stems are suitable for building poles, tool handles and firewood.
Growth and development
Acokanthera schimperi has a moderate growth rate. In Kenya fruiting occurs from February to March and in Tanzania from April to July. The flowers are pollinated chiefly by bees and seeds dispersed by animals.
Acokanthera schimperi occurs at the margins of dry forest, in relict forest, thickets, grasslands and bushland, at 1100–2400 m altitude and with 600–1000 mm annual rainfall. It is drought resistant. It prefers well-drained, red or black rocky soils, but also grows on black cotton soil and poor soil of dry sites. Lowland distribution appears to be associated with human introduction.
Propagation and planting
Acokanthera schimperi regenerates naturally by seed. In Kenya and Ethiopia wildlings are transplanted to home gardens. The seeds have high moisture content and lose viability easily under ambient conditions and on storage. There are 400–450 seeds per kg. Seed germination is low.
Acokanthera schimperi can be pruned and pollarded in intercropping systems.
Acokanthera schimperi is not equally poisonous throughout the year. The toxic potential of trees is sometimes established by observation of dead insects or dead birds under the tree. The fruits are handpicked or harvested with aid of a pole.
One kg of wood of Acokanthera schimperi, together with 250 g of roots and 100 g of leaves yields 100 g of poison. The wood of twigs and roots yields 0.2% of ouabain.
Handling after harvest
Stem wood is chopped into 15 cm long pieces. Chopped stems, roots, leaves and less commonly seeds of Acokanthera schimperi, together with animal and other plant additives, are put in a large clay container filled with water, and boiled with occasional stirring for up to 10 hours over a fire in a secluded place. Additional water is added in case the water evaporates before the poison is ready. In some communities, the making of the poison is complex, and ritual aspects, such as chanting, are observed to improve the efficacy of the poison. Once all the water has evaporated, a thick sticky black substance is left in the container. Used plant parts are discarded and the substance is then cut into pieces, put into containers or wrapped. Before use, the sticky extract is made into balls and spread in small amounts on arrow tips. Plant and animal parts are frequently added to increase poison potency and for magical reasons. In Kenya many different plant additives are used together with poison from Acokanthera schimperi, whereas in Tanzania mainly Strophanthus spp. are used, and to a lesser amount Euphorbia candelabrum Kotschy and Urginea spp. In Rwanda mainly Strychnos usambarensis Gilg is mixed with the poison. The poison is traded the same way as 150 years ago, in the form of a characteristic ‘poison cigar’, where the poison is packed securely in maize leaves. It is sometimes sold wrapped in paper, leaves, cloths, or foil or in open cans. The poison needs to be stored in a cool, dark place, and will keep its potency for decades.
Acokanthera schimperi is not at risk but considered rare in southern Ethiopia.
Acokanthera schimperi plants from the coastal zone of Kenya contain a high percentage of ouabain, and could thus have medical and commercial potential in congestive heart failure treatment.
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Correct citation of this article:
Bethwell, O.O., 2007. Acokanthera schimperi (A.DC.) Schweinf. In: Schmelzer, G.H. & Gurib-Fakim, A. (Editors). Prota 11(1): Medicinal plants/Plantes médicinales 1. [CD-Rom]. PROTA, Wageningen, Netherlands.
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