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Orbea decaisneana (Lem.) Bruyns

Protologue
Aloe 37(4): 74 (2001).
Family
Asclepiadaceae (APG: Apocynaceae)
Chromosome number
2n = 22
Synonyms
Caralluma decaisneana (Lem.) N.E.Br. (1892), Stapelia decaisneana (Lem.) A.Chev. (1934), Pachycymbium decaisneanum (Lem.) M.G.Gilbert (1990), Angolluma decaisneana (Lem.) L.E.Newton (1993).
Origin and geographic distribution
Orbea decaisneana occurs in Mauritania, Senegal, Mali, Burkina Faso, Niger, Sudan, Algeria and Morocco.
Uses
In Senegal an extract of the aerial parts enters in a treatment for mental problems and epilepsy. Plant sap is applied to teeth with caries. Plant sap is considered very toxic and milk is taken as an antidote to poisoning. In Mali dried powdered stems are thrown in the water as fish poison; it is considered slow-acting. In Niger the stems are macerated in water and the extract used as bait for guinea fowl. In Algeria nomads put the plant sap or pulped plants on bait to poison jackal. It is sometimes used as criminal poison.
Orbea decaisneana is sold on the internet to succulent collectors.
Properties
The toxins of Orbea decaisneana have not been chemically characterized. Preliminary toxicological investigations showed that the administration of a hot alcohol extract of the dried plants, intraperitoneally (i.p) in mouse, gave an LD50 = 2 g/kg, a water extract gave an LD50 = 12 g/kg mouse i.p., while the fresh plant sap gave an LD50 = 2.2 g/kg mouse i.p. The mice became restless with signs of nerve impairment, followed by paralysis of the hind legs, dilated eyes, and finally death in 3–48 hours.
Botany
Small perennial herb up to 20 cm tall, forming diffuse mats to c. 50 cm in diameter; stems succulent, 1–4 cm × 1.2–1.5 cm, excluding teeth, spreading, grey-green, mottled with brown to purple; tubercles (the ‘teeth’) 10–15 mm long, in 4 rows along the stem with a slight groove among them, tapering to slender apex. Leaves rudimentary at tubercle apex; stipular denticles absent. Inflorescence 1–3 per stem near apex, each with 1–5(–10) flowers developing in gradual succession; peduncle absent; bracts lanceolate, c. 1 mm long. Flowers bisexual, regular, 5-merous, with fetid smell; pedicel 1–5 mm long, up to 2(–3) mm in diameter, spreading; sepals lanceolate, 3–5 mm long, acute; corolla 8–15 mm long, 1.5–2.5 cm in diameter, campanulate, outside cream mottled with brown, inside dark purple sometimes yellow towards base of tube, with small papillae, each tipped with fine white bristle, tube 4–6 mm long, 6–8 mm in diameter, cup-shaped, lobes ovate-lanceolate, 7–12 mm × 5.5–7 mm, ascending then spreading, margins reflexed; corona c. 4 mm × c. 5 mm, purple, outer lobes c. 2 mm long, pouch-like, inner lobes c. 1 mm long, slightly longer than style head; style head pentagonal. Fruit a pair of follicles.
Orbea belongs to the subtribe Stapeliinae (tribe Ceropegieae), comprising 36 genera and c. 700 species in the Old World. The Orbea complex comprises about 55 species and includes the formerly recognized genera Orbeopsis, Pachycymbium and Angolluma, whereas the separation or inclusion of Orbeanthus and Ballyanthus is still in discussion. Orbea is widely distributed in Africa, and also includes 6 species in southwestern Arabia. Within Africa there are 2 centres of diversity, a northeastern centre from Tanzania to Arabia and a southern centre in southern Africa. Only Orbea decaisneana has spread to West and northern Africa.
Several other Orbea species in tropical Africa are medicinally used. Orbea dummeri (N.E.Br.) Bruyns occurs in Burundi, Kenya, Tanzania and Uganda. The Turkana people in Kenya drink a decoction of the stems with milk or chew the stems to treat chest pains. Fresh plant sap is squeezed on wounds to heal them. In Uganda the dried and powdered whole plants are put in water and the filtrate is put in the ear to help evacuate ear wax and to treat headache. In Tanzania the latex is applied as ear drops to treat earache. Orbea semota (N.E.Br.) L.C.Leach occurs in Rwanda, Kenya and Tanzania. In Tanzania the sap from the pounded stems is applied to wounds and ulcers. The fetid smell is mainly caused by butanoic acid (26.6%). Orbea lutea (N.E.Br.) Bruyns occurs in southern Africa. The Owambo people in Namibia take an extract of the entire plant to treat rabies. The Khu Bushmen in Namibia slightly roast the stems before eating them, but the taste is somewhat disagreeable and the plant is only eaten as famine food. The stems are heavily grazed by cattle.
Ecology
Orbea decaisneana occurs on desert margins in dry grasslands, among stones on slopes on granite and on limestone outcrops, from sea-level up to 2000 m altitude.
Genetic resources and breeding
Orbea decaisneana has a relatively large area of distribution but is poorly recorded and it is not known whether it is threatened by genetic erosion.
Prospects
Orbea decaisneana will remain only of local importance as a medicinal plant as it is very toxic, unless chemical and pharmacological analyses show its potential.
Major references
• Albers, F. & Meve, U. (Editors), 2002. Illustrated handbook of succulent plants. Asclepiadaceae. Springer, Berlin, Heidelberg, Germany. 318 pp.
• Bruyns, P.V., 2002. Monograph of Orbea and Ballyanthus (Apocynaceae - Asclepiadoideae - Ceropegieae). Systematic Botany Monographs 63: 1–196.
• Neuwinger, H.D., 2000. African traditional medicine: a dictionary of plant use and applications. Medpharm Scientific, Stuttgart, Germany. 589 pp.
Other references
• Burkill, H.M., 1985. The useful plants of West Tropical Africa. 2nd Edition. Volume 1, Families A–D. Royal Botanic Gardens, Kew, Richmond, United Kingdom. 960 pp.
• Burkill, H.M., 2000. The useful plants of West Tropical Africa. 2nd Edition. Volume 5, Families S–Z, Addenda. Royal Botanic Gardens, Kew, Richmond, United Kingdom. 686 pp.
• Jürgens, A., Dötterl, S. & Meve, U., 2006. The chemical nature of fetid floral odours in stapeliads (Apocynaceae-Asclepiadoideae-Ceropegieae). New Phytologist 172(3): 452–468.
• Morgan, W.T.W., 1981. Ethnobotany of the Turkana: use of plants by a pastoral people and their livestock in Kenya. Economic Botany 35(1): 96–130.
• SEPASAL, 2009. Orbea lutea. [Internet] Survey of Economic Plants for Arid and Semi-Arid Lands (SEPASAL) database. Royal Botanic Gardens, Kew, Richmond, United Kingdom. http://www.kew.org/ ceb/sepasal/. Accessed July 2009.
Author(s)
G.H. Schmelzer
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands


Editors
G.H. Schmelzer
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
A. Gurib-Fakim
Faculty of Science, University of Mauritius, Réduit, Mauritius
Associate editors
R. Arroo
Leicester School of Pharmacy, Natural Products Research, De Montfort University, The Gateway, Leicester LE1 9BH, United Kingdom
Photo editor
G.H. Schmelzer
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands

Correct citation of this article:
Schmelzer, G.H., 2010. Orbea decaisneana (Lem.) Bruyns. In: Schmelzer, G.H. & Gurib-Fakim, A. (Editors). Prota 11(2): Medicinal plants/Plantes médicinales 2. [CD-Rom]. PROTA, Wageningen, Netherlands.

obtained from The Asclepiad Exhibition




obtained from The Asclepiad Exhibition




obtained from Asclepidarium