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Strophanthus kombe Oliv.

Protologue
Hook.f., Icon. pl. 11: 79, t. 1098 (1871).
Family
Apocynaceae
Synonyms
Strophanthus hispidus DC. var. kombe (Oliv.) Holmes (1890).
Vernacular names
Kombi (Po). Mchoki (Sw).
Origin and geographic distribution
Strophanthus kombe occurs naturally in eastern and southern Africa, from south-eastern Kenya and eastern Tanzania to eastern Namibia (Caprivi Strip), Botswana, Zimbabwe, Mozambique and northern South Africa. It is not planted on a large scale.
Uses
The seeds and roots of Strophanthus kombe have been used in the preparation of arrow poison since prehistoric times throughout the species’ range. Game wounded by a poisoned arrow dies quickly, while the flesh can be eaten without ill effect. However, flesh immediately surrounding the wound is usually discarded.
Nowadays, the glycoside mixture from the seeds (‘Semen strophanthi’) is used medicinally as a heart stimulant. It is used in a number of medicines in several European countries for its influence on blood circulation, especially in cases of chronic heart weakness. The Giriama people of coastal Kenya use the leaves to make a charm used in a cleansing ritual.
Production and international trade
Although seeds of Strophanthus kombe are exported from Africa, mainly to Europe, but also to the United States and Japan, there are no data on amounts and value.
Properties
More than a dozen cardiac glycosides (cardenolides) have been isolated from Strophanthus kombe. Compared to Digitalis cardenolides, those of Strophanthus kombe are characterized by highly oxygenated aglycones. The glycosides are most abundant in the seed and are responsible for the activity as arrow poison and as cardiac and vascular stimulant. The seeds contain about 4 g/100 g of a mixture of glycosides called strophanthin-K. It is a whitish, crystalline powder which is freely soluble in water, and is readily hydrolyzed into genins and sugars when warmed in acidic conditions. The composition of the mixture varies, but has as major component k-strophanthoside (k-strophanthin-γ). Other glycosides in the mixture, based on the aglycone strophanthidin, are cymarin ( k-strophanthin-α), k-strophanthin-β, erysimoside and helveticoside (erysimotoxin). Minor components with periplogenin as aglycone are periplocymarin, periplocin and emicymarin; minor components with strophanthidol as aglycone are cymarol, k- strophanthol-β, k-strophanthol-γ, helveticosol and erysimosol. All compounds are highly toxic. The seeds of Strophanthus kombe provide the precursor for the semi-synthetic compound acetylstrophanthidin, which is of clinical interest because of its rapid onset of vascular stimulant action when administered intravenously. The roots and fruits also contain considerable amounts of cardiac glycosides, while the leaves contain mainly resin.
k-Strophanthin-β has a similar effect as ouabain (from Strophanthus gratus (Wall. & Hook.) Baill.) or Digitalis glycosides and causes a positive inotropic effect and electrophysiological changes in the heart by inhibiting the membrane-bound Na+-K+-ATPase pump responsible for Na+-K+ exchange. It should be used with great care and under strict medical direction because of its strength and narrow pharmaceutical range. It may cause intense local irritation when administered by hypodermic injection. In urgent cases, the effects upon circulation can be obtained almost immediately by means of intravenous injection. It has stronger diuretic properties than other cardiac glycosides, which is of value in cases complicated by oedema, but is also more likely to cause digestive disturbances
Adulterations and substitutes
It is likely that the seeds of several Strophanthus species are sometimes mixed before they are exported. Strophanthus courmontii Sacleux ex Franch., Strophanthus eminii Asch. & Pax and Strophanthus nicholsonii Holmes, all from more or less the same region as Strophanthus kombe, have seeds which resemble those of the latter and are probably mixed with them in trade.
Description
Deciduous shrub up to 3.5 m tall or liana up to 20 m long, with clear, white or yellow exudate, roots thick and fleshy, necklace-shaped; stem up to 10 cm in diameter; bark reddish brown or grey-brown; branches with few to many lenticels, dark brown, dark grey or black. Leaves decussately opposite, simple and entire; stipules absent; petiole 1.5–5 mm long; blade ovate or elliptical, less often obovate or nearly orbicular, 8–23.5 cm × 5–16.5 cm, base cuneate, rounded or slightly cordate, apex obtuse, acute or acuminate, papery, in young leaves densely hairy on both sides, in older leaves glabrescent above. Inflorescence a rather congested terminal dichasial cyme, on short branches or in the forks, 1–12-flowered; peduncle 2–14(–25) mm long; bracts linear or narrowly obovate, 5–23 mm long. Flowers bisexual, regular, 5-merous, fragrant; pedicel 3–14(–20) mm long; sepals free, slightly unequal, narrowly ovate or linear, 9–20(–27) mm long, acute; corolla tube 13–24 mm long, widening at 45–66% of its length into a cup-shaped upper part, at the mouth (6–)8–14 mm wide, densely hairy outside except for the base, sparsely hairy inside except for the base, white turning yellow on both sides, red-spotted and -streaked inside, corona lobes tongue-shaped, 1–3 mm long, rounded, fleshy, minutely hairy, yellow and pink-spotted, the pink turning purple, corolla lobes ovate, gradually or rather abruptly narrowing into the 1 mm wide pendulous tails, lobes including the tail 10–16(–20) cm long, hairy except for the inner side of the tails, white and turning yellow, tails yellow; stamens inserted at 7–12 mm from the base of the corolla tube, included; ovary half-inferior, 2-celled, style 6.5–13.5 mm long, ending in a ringlike pistil head surrounding the minute stigma. Fruit consisting of 2 ellipsoid follicles 15–47 cm × 1.5–2.5 cm, tapering towards the apex and ending in a small or large knob, 2-valved, divergent at 180°, wall thick and hard, densely hairy in young fruits but glabrescent when maturing, many-seeded. Seeds spindle-shaped, 11–21 mm × 2.5–4.5 mm × 1.5 mm, densely hairy, at apex with a long beak up to 10 cm long, glabrous in lower half, upper half with long hairs, top including the hairs up to 8 cm long. Seedling with epigeal germination; cotyledons elliptical or ovate, obtuse at apex, glabrous; first leaves resembling leaves of mature plants but usually narrower.
Other botanical information
Strophanthus comprises 38 species, of which 30 occur in continental Africa, 1 in Madagascar and 7 in Asia, from India to South-East Asia. Many of these species are used medicinally. Strophanthus kombe is closely related to Strophanthus hispidus DC. from West and Central Africa, which differs in more widely divergent follicles and wider outer sepals.
Growth and development
Flowering of Strophanthus kombe occurs towards the end of the dry season and the beginning of the rainy season. Nothing is known about pollinators, although flower structure and colouring suggest butterflies. Fruits mature in the dry season. Seeds are dispersed by wind.
Ecology
Strophanthus kombe occurs in coastal forest, gallery forest, riparian thickets and woodland, often on inselbergs, from sea-level up to 1100 m altitude.
Propagation and planting
At the Royal Botanic Gardens, Kew, United Kingdom, semi-ripe cuttings are taken in April. Cuttings are dipped into a rooting hormone and then placed in a mist unit in pots containing a coir and perlite mix, at a temperature of 25°C and relative humidity of 80%. When they have rooted, after about 4 weeks, they are potted up.
Management
Seeds intended for trade are usually collected from wild plants. As far as is known, Strophanthus kombe is not cultivated on a large scale.
Handling after harvest
In preparing the arrow poison, the seeds are pounded to a pulp after removal of the tuft of hairs. An adhesive is added (e.g. Euphorbia latex or saliva), the mixture is sometimes exposed to strong sunlight for some hours, and subsequently smeared along the point of the arrow.
Strophanthus seeds should be preserved in tightly closed containers, and a few drops of chloroform or carbon tetrachloride should be added from time to time to prevent insect attack. The drug is extracted with absolute alcohol, the oil is removed from the percolate with petroleum ether, and the glycosides are subsequently converted into strophanthidin by boiling with hydrochloric acid.
Genetic resources
There are no indications that Strophanthus kombe is at risk of genetic erosion. Large germplasm collections of Strophanthus kombe do not exist. As the glycoside concentration differs per population, variability studies are needed to evaluate this.
Prospects
Strophanthus kombe is a source of compounds that are useful in treating heart failure and blood circulation disorders. The use of strophanthin-K, k-strophanthin-β and acetylstrophanthidin is likely to continue, but the use of strophanthins as cardiac medicine had its peak from 1950 to 1970 and has declined since. The biotransformation abilities of Strophanthus plant cell and tissue cultures may provide new, more effective and safer cardiac glycosides.
Major references
• Beentje, H.J., 1982. A monograph on Strophanthus DC. (Apocynaceae). Mededelingen Landbouwhogeschool Wageningen 82–4. Wageningen, Netherlands. 191 pp.
• Grosa, G., Allegrone, G. & Del Grosso, E., 2005. LC-ESI-MS/MS characterization of strophanthin-K. Journal of Pharmaceutical and Biomedical Analysis 38(1): 79–86.
• Kawaguchi, K., Hirotani, M. & Furuya, T., 1993. Strophanthus species (members of the dogbane family): in vitro culture and the production of cardenolides. In: Bajaj, Y.P.S. (Editor). Biotechnology in agriculture and forestry. Volume 21. Medicinal and Aromatic Plants IV. Springer-Verlag, Berlin, Heidelberg, Germany. pp. 371–386.
• Neuwinger, H.D., 1996. African ethnobotany: poisons and drugs. Chapman & Hall, London, United Kingdom. 941 pp.
Other references
• Beentje, H.J. & Cooke, D., 2000. Strophanthus sarmentosus: Apocynaceae. Curtis’s Botanical Magazine 17(4): 202–207.
• Gelfand, M., Mavi, S., Drummond, R.B. & Ndemera, B., 1985. The traditional medical practitioner in Zimbabwe: his principles of practice and pharmacopoeia. Mambo Press, Gweru, Zimbabwe. 411 pp.
• Pakia, M. & Cooke, J.A., 2003. The ethnobotany of the Midzichenda tribes of the coastal forest areas in Kenya: 2. Medicinal plant uses. South African Journal of Botany 69(3): 382–395.
• van Wyk, B.E. & Gericke, N., 2000. People’s plants: a guide to useful plants of southern Africa. Briza Publications, Pretoria, South Africa. 351 pp.
• Williamson, J., 1955. Useful plants of Nyasaland. The Government Printer, Zomba, Nyasaland. 168 pp.
Sources of illustration
• Beentje, H.J., 1982. A monograph on Strophanthus DC. (Apocynaceae). Mededelingen Landbouwhogeschool Wageningen 82–4. Wageningen, Netherlands. 191 pp.
Author(s)
H.J. Beentje
Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3AB, United Kingdom


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
C.H. Bosch
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
M.S.J. Simmonds
Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3AB, United Kingdom
R. Arroo
Leicester School of Pharmacy, Natural Products Research, De Montfort University, The Gateway, Leicester LE1 9BH, United Kingdom
A. de Ruijter
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
General editors
R.H.M.J. Lemmens
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
L.P.A. Oyen
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
Photo editor
A. de Ruijter
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands

Correct citation of this article:
Beentje, H.J., 2006. Strophanthus kombe Oliv. In: Schmelzer, G.H. & Gurib-Fakim, A. (Editors). Prota 11(1): Medicinal plants/Plantes médicinales 1. [CD-Rom]. PROTA, Wageningen, Netherlands.
Distribution Map wild


1, mature leaf; 2, flowering branch; 3, flower; 4, fruit, one follicle removed; 5, seed.
Redrawn and adapted by M.M. Spitteler



inflorescence
obtained from
B. Wursten