Acokanthera oppositifolia (PROTA)

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Plant Resources of Tropical Africa
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Acokanthera oppositifolia (Lam.) Codd


Protologue: Bothalia 7: 448 (1961).
Family: Apocynaceae

Synonyms

  • Acokanthera longiflora Stapf (1922).

Vernacular names

  • Bushman poison, wintersweet, common poison bush (En).
  • Msunguti (Sw).

Origin and geographic distribution

Acokanthera oppositifolia occurs from Kenya south to South Africa, and to southern DR Congo in the west.

Uses

Bark, root, wood and leaves are used in the preparation of arrow poison, and also for hunting, suicide and homicide. The only treatment against the poison is immediate excision of the flesh around the wound. The poison is also used for killing wild animals (hyenas, elephants, buffaloes, leopards, lions) and stray dogs. Fatal accidents have been caused by eating meat grilled over a fire of sticks from this tree. To treat snakebites and spider bites, a small amount of the leaves is eaten, a leaf or root decoction is drunk and the leaf or root pulp is rubbed into the wound. Alternatively, root powder is sniffed and a dressing made of roots or leaves is put on the swollen part. A root infusion is taken to treat syphilis. In South Africa root powder or leaf powder is sniffed to cure headache, while a leaf infusion is used as a nasal spray for this purpose. Small pieces of the stem are chewed against toothache. A leaf infusion is taken to treat abdominal pain, colds, measles and blood poisoning. A root infusion is taken to expel tapeworm and to treat excessive and irregular menstruation. Poisoning of livestock is rare, but the risk increases during droughts.

The pulp of the ripe fruit is edible and has a sweetish bitter taste. It is relished by birds and animals and has also been used in making jams and preserves. The unripe fruits and seeds are highly poisonous, and accidental poisoning of children has been recorded. Children use the latex of the fruit as chewing gum. Acokanthera oppositifolia has beautiful flowers and is grown as an ornamental although it is poisonous. It is sometimes marketed as a container plant in South Africa and in subtropical and temperate regions.

Production and international trade

The poison made from the wood, leaves and roots of Acokanthera oppositifolia is traded in small amounts among tribes. Arrow tips are also smeared with the poison in exchange for money. There are no data on traded volumes or value.

Properties

All parts of Acokanthera oppositifolia, except for the pulp of the ripe fruit, contain large amounts of cardiac glycosides (cardenolides), of which about 15 have been identified. The glycosides are responsible for the activity as arrow poison, but also act as cardiac stimulant. The main compound is acovenoside A (1.2–2.4%), with acovenosigenin as aglycone, followed by acolongifloroside K (acolongifloriside K) (0.3–0.4%), with ouabagenin as aglycone. Acokanthera oppositifolia plants from South Africa contain twice as much acovenoside A as plants from Kenya, but less acolongifloroside K. Minor components include acovenoside C, opposide, acofrioside L, acolongifloroside H and and traces of ouabain. The constitution is location dependent.

Patent applications have been submitted for the use of acovenoside A for treating muscle pain. Acolongifloroside K, opposide and ouabain 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 treat patients suffering from congestive heart failure. In higher doses, cardiac glycosides have a direct inhibiting action on the atrioventricular conduction and cause 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. Animals that eat the leaves or immature fruit show dullness, followed by violent spasms, paralysis and finally death.

Adulterations and substitutes

Another arrow poison plant, Strophanthus gratus (Wall. & Hook.) Baill., contains mainly ouabain, and to a lesser extent acolongifloroside K.

Description

Evergreen shrub or small tree up to 6(–7) m tall; bark brown, deeply fissured; young branches reddish, glabrous, conspicuously angled and ribbed. Leaves decussately opposite, simple and entire; stipules absent; petiole 2–6 mm long; blade obovate to elliptical, 4–13.5 cm × 1.5–8 cm, base cuneate or rounded, apex acute, obtuse or rounded, with hard mucro, leathery, glossy, usually glabrous, pinnately veined, lateral veins prominent, without looping connections. Inflorescence a dense axillary cyme, many-flowered. Flowers bisexual, regular, 5-merous, fragrant; sepals free, ovate to lanceolate, (1.5–)2–3.5 mm long, apex acuminate to acute, shortly hairy or glabrous outside, ciliate; corolla tube cylindrical, 6.5–20 mm long, shortly hairy outside, inside sparsely hairy in the upper half and wrinkled below, pink or red, lobes broadly elliptical, 2–5 mm long, apex acute, shortly hairy on both sides, ciliate, white; stamens inserted at 12.5–15 mm from the base of the corolla tube, slightly exserted; ovary superior, ellipsoid, 2-celled, style slender, 11–16 mm long, stigma minutely bifid. Fruit an ellipsoid berry 1.5–3(–4) cm long, purple when ripe, pulp green to deep red, 1–2-seeded. Seeds ellipsoid, plano-convex, 6–10 mm long, smooth, glabrous.

Other botanical information

Acokanthera comprises 5 species and is restricted to Africa, with one species also found in Yemen. It is related to Carissa.

Growth and development

Acokanthera oppositifolia is a moderately fast growing tree, which is drought and shade tolerant, and frost resistant. It flowers from late January to March, and fruits from April to July in South Africa and Tanzania; in Kenya it fruits from February to March. Insects are the major pollinators and animals the major seed dispersers.

Ecology

Acokanthera oppositifolia occurs at 1000–2400 m altitude in areas with an annual rainfall of 600–1000 mm. It thrives in rocky, red clay and clay-loam soils, often on termite mounds. It is usually found on rocky hillsides, in riparian forest edges, coastal bush, or open woodland.

Propagation and planting

Acokanthera oppositifolia can be propagated by seed or semi-hardwood cuttings. Seeds require no pretreatment and should be sown fresh owing to their poor storage nature. They have a high water content and lose their viability easily on storage. Wildlings can also be used for propagation.

Management

Acokanthera oppositifolia is commonly left standing in pasture fields and farm land as a shade plant. Pruning and pollarding can be used in managing the tree.

Harvesting

The fruits are handpicked or harvested with the aid of a pole.

Yield

To prepare 100 g of Acokanthera oppositifolia poison, 1 kg of wood, together with 250 g roots and 100 g leaves are needed.

Handling after harvest

The wood or roots of Acokanthera oppositifolia are boiled in water for a long time until a tar-like substance is obtained. The latter is filtered and stored in an airtight container away from children. Addition of plant and animal parts to the arrow poison is common in southern Africa. Fresh latex of Euphorbia spp. and bulbs of Boophone disticha (L.f.) Herb. are commonly used additives for poison production. Numerous animal additives, e.g. poisonous spiders, insects, dried and powdered cobra and viper glands may also be added to increase poison toxicity.

Genetic resources

Acokanthera oppositifolia is a relatively common species, and there are no indications that it is at risk of genetic erosion. In southern Africa it is an invasive colonizer with weedy tendencies.

Prospects

The cardenolides isolated from Acokanthera oppositifolia are highly poisonous. Most of them have not been pharmacologically investigated, and more research is needed to evaluate the possible prospects of the various compounds. Acokanthera oppositifolia has attractive leathery, dark green leaves, beautiful, fragrant inflorescences and is drought and frost tolerant; these characteristics make it interesting as an ornamental, although its poisonous properties make it dangerous.

Major references

  • Coates Palgrave, K., 1983. Trees of southern Africa. 2nd Edition. Struik Publishers, Cape Town, South Africa. 959 pp.
  • Hauschild-Rogat, P., Weiss, E. & Reichstein, T., 1967. Glycosides and aglycons. CCCI. Cardenolides of Acokanthera oppositifolia. 3. Isolation of additional cardenolides and partial structural elucidation. Helvetica Chimica Acta 50(8): 2299–2321.
  • Kupicha, F.K., 1982. Studies on African Apocynaceae: the genus Acokanthera. Kew Bulletin 37(1): 41–67.
  • Maundu, P. & Tengnäs, B. (Editors), 2005. Useful trees and shrubs for Kenya. World Agroforestry Centre - East and Central Africa Regional Programme (ICRAF-ECA), Technical Handbook 35, Nairobi, Kenya. 484 pp.
  • Neuwinger, H.D., 1996. African ethnobotany: poisons and drugs. Chapman & Hall, London, United Kingdom. 941 pp.
  • Neuwinger, H.D., 2000. African traditional medicine: a dictionary of plant use and applications. Medpharm Scientific, Stuttgart, Germany. 589 pp.
  • Omino, E.A., 2002. Apocynaceae (part 1). In: Beentje, H.J. & Ghazanfar, S.A. (Editors). Flora of Tropical East Africa. A.A. Balkema, Rotterdam, Netherlands. 116 pp.

Other references

  • Dharani, N., 2002. Field guide to common trees and shrubs of East Africa. Struik Publishers, Cape Town, South Africa. 320 pp.
  • Hanna, A.G., Elgamal, M.H.A., Hassan, A.Z., Duddeck, H., Simon, A., Kovács, J. & Tóth, G., 1998. Complete 1H and 13C signal assignments of 5b-cardenolides isolated from Acokanthera spectabilis Hook.f. Magnetic Resonance in Chemistry 36(12): 936–942.
  • Karawya, M.S., Abdel Wahab, S.M. & Niazi, H.M., 1974. Assay of cardinolides in Acokanthera spectabilis. Planta Medica 25(1): 17–21.
  • Kokwaro, J.O., 1993. Medicinal plants of East Africa. 2nd Edition. Kenya Literature Bureau, Nairobi, Kenya. 401 pp.
  • Laudadio, C. & Davis, M., 2003. Cardiac glycosides for treating muscle pain and spasm. U.S. Patent Application US 2003229029. 6 pp.
  • Maundu, P., Berger, D., Saitabau, C., Nasieku, J., Kipelian, M., Mathenge, S., Morimoto, Y. & Höft, R., 2001. Ethnobotany of the Loita Maasai. Towards community management of the forest of the Lost Child. Experiences from the Loita Ethnobotany Project. UNESCO People and Plants Working Paper 8, Paris, France. 34 pp.
  • Maundu, P.M., Ngugi, G.W. & Kabuye, C.H.S., 1999. Traditional food plants of Kenya. Kenya Resource Centre for Indigenous Knowledge (KENRIK), Nairobi, Kenya. 270 pp.
  • Pieri, F., Arnould Guerin, M.L. & Sefraoui, E.H., 1992. Cardiotonic glycosides from Acokanthera spectabilis. Fitoterapia 63(4): 333–336.
  • Ruffo, C.K., Birnie, A. & Tengnäs, B., 2002. Edible wild plants of Tanzania. Technical Handbook No 27. Regional Land Management Unit/ SIDA, Nairobi, Kenya. 766 pp.
  • Tyiso, S. & Bhat, R.B., 1998. Medicinal plants used for child welfare in the Transkei region of the Eastern Cape (South Africa). Journal of Applied Botany 72(3–4): 92–98.
  • van Wyk, B.E., van Heerden, F. & van Oudtshoorn, B., 2002. Poisonous plants of South Africa. Briza Publications, Pretoria, South Africa. 288 pp.
  • van Wyk, B.E., van Oudtshoorn, B. & Gericke, N., 1997. Medicinal plants of South Africa. Briza Publications, Pretoria, South Africa. 304 pp.
  • Watt, J.M. & Breyer-Brandwijk, M.G., 1962. The medicinal and poisonous plants of southern and eastern Africa. 2nd Edition. E. and S. Livingstone, London, United Kingdom. 1457 pp.

Sources of illustration

  • Kupicha, F.K., 1982. Studies on African Apocynaceae: the genus Acokanthera. Kew Bulletin 37(1): 41–67.

Author(s)

  • O.O. Bethwell, Department of Natural Sciences, Catholic University of Eastern Africa, P.O. Box 62157, 00200 Nairobi, Kenya

Correct citation of this article

Bethwell, O.O., 2007. Acokanthera oppositifolia (Lam.) Codd. In: Schmelzer, G.H. & Gurib-Fakim, A. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands. Accessed 28 November 2017.