Adenium obesum (Forssk.) Roem.

Family

Apocynaceae

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Chromosome number

2n = 22

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Synonyms

Adenium somalense Balf.f. (1888), Adenium socotranum Vierh. (1904).

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Vernacular names

Desert rose, impala lily (En). Rose du désert, baobab chacal, faux baobab, lis des impalas, pied d’éléphant (Fr). Rosa do deserto, baobá exótica, djindje pété (Po). Mdagu, mdaguwande, mwanja (Sw).

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Origin and geographic distribution

Adenium obesum occurs from Senegal to Ethiopia and from Somalia to Tanzania. It also occurs in Egypt, Saudi Arabia, Oman and Yemen, including Socotra; it is uncertain whether it occurs naturally in West Africa or has been introduced and become naturalized. Adenium obesum is naturalized in Sri Lanka and parts of south-eastern Asia, e.g. Thailand. As an ornamental it is cultivated worldwide.

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Uses

In a wide area of Africa the root sap or sometimes the wood or stem latex of Adenium obesum is used to prepare arrow poison. The poison is popular for hunting large game as it kills quickly and the hunted animal dies within 2 km from the place where it was shot. The Hadza people of Tanzania use the sap by itself or sometimes in combination with poison from Strophanthus eminii Asch. & Pax, while the Duruma people of Kenya use the stem latex, sometimes in combination with the roots and wood of Acokanthera schimperi (A.DC.) Schweinf. or the latex of Synadenium pereskiifolium (Baill.) Guillaumin. The use of Adenium obesum arrow poison is also reported from Senegal, Nigeria and Cameroon. A decoction of the bark and leaves is widely used as fish poison. This use is reported from Nigeria, Cameroon and East Africa. In Mauritania and Senegal preparations from Adenium obesum are used as ordeal poison and for criminal purposes.
Adenium obesum is important in traditional medicine. In the Sahel a decoction from the roots, alone or in combination with other plants, is used to treat venereal diseases; a root or bark extract is used as a bath or lotion to treat skin diseases and to kill lice, while latex is applied to decaying teeth and septic wounds. In Somalia a root decoction as nose drops is prescribed for rhinitis. In northern Kenya latex is rubbed on the head against lice and powdered stems are applied to kill skin parasites of camels and cattle. The bark is chewed as an abortifacient.
Adenium obesum is planted fairly frequently for its curious form and attractive flowers. Sometimes it is planted as a live fence. In Tanzania it is planted to mark the position of graves. The wood is sometimes used as fuel.

Production and international trade

Seed and plants of Adenium obesum are traded internationally for ornamental purposes.

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Properties

In Adenium obesum the presence of some 30 cardiotoxic glycosides has been demonstrated, which act in a similar way as digitalis from Digitalis. Digitalis acts upon the Na⁺K⁺-ATPase enzyme that regulates the concentrations of Na⁺ and K⁺ ions in body cells and so also modifies the Ca⁺⁺ concentration. In low doses it is used to treat congestive heart failure (CHF) and heart rhythm problems (atrial arrhythmias), but in high doses it leads to systolic heart failure and death.
Several of the cardiac glycosides from Adenium obesum have oleandrigenin as aglycone moiety, e.g. hongheloside A (with D-cymarose), hongheloside C (with D-cymarose and D-glucose) and 16-acetylstrospeside (with D-digitalose). Other glycosides include: hongheline (composed of digitoxigenin with D-thevetose), somaline (composed of digitoxigenin with D-cymarose) and digitalinum verum (composed of gitoxigenin with D-digitalose and D-glucose). The roots and stems contain the same glycosides and in similar amounts. Oleandrigenin and some of the glycosides derived from it have cytotoxic effects and are being studied as potential components of anticancer drugs.
The ethanol extract of the roots slows down the growth of Bacillus subtilis, but has not shown activity against Pseudomonas aeruginosa, Staphylococcus aureus or Candida albida. Extracts from the root have shown a cytotoxic effect against several carcinoma cell lines. The aqueous stem bark extract is a potential acaricide as it shows high toxicity on all stadia of development of the ticks Amblyomma spp. and Boophilus spp.

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Description

Succulent shrub or small tree, up to 4(–6) m tall, sometimes with a fleshy taproot; stem swollen at base up to 1(–2) m in diameter; bark pale greyish-green, grey or brown, smooth, with sticky, clear or white latex; branchlets glabrescent, pubescent at apex. Leaves arranged spirally, clustered at the end of branchlets, simple; stipules minute or absent; petiole up to 4 mm long; blade linear to obovate, 3–12(–17) cm × 0.2–6 cm, base cuneate, apex acute to rounded or emarginate, entire, slightly glaucous, dull green or pale green, leathery, pinnately veined with distinct or indistinct lateral veins. Inflorescence a more or less dense terminal cyme; bracts linear to narrowly oblong, 3–8 mm long, acuminate, pubescent. Flowers bisexual, regular, 5-merous, showy, usually appearing before the leaves; pedicel 5–9 mm long; sepals narrowly oblong to narrowly ovate, 6–12 mm long, hairy; corolla with funnel-shaped tube 2–4.5 cm × 0. 9–1.7 cm, reddish-pink to white suffused with pink, sometimes red-striped inside the throat, hairy to glabrous outside, glandular hairy on main veins inside, lobes 1–3 cm × 0.5–2.5 cm, spreading, pale pink to red with darker margins; stamens inserted near base of corolla tube, included or exserted, anthers forming a cone covering the pistil, base sagittate, 5–7 mm long, with long apical appendices; ovary superior, composed of 2 free carpels, glabrous, styles fused, slender, with well-developed clavuncula. Fruit consisting of 2 linear-oblong follicles, coherent at the base, 11–22 cm long, tapering at both ends, recurved, grey to pale grey-brown, opening by a longitudinal slit, many-seeded. Seeds linear-oblong, 10–14 mm long, pale brown, slightly rough, with tufts of long dirty white hairs at both ends.

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Other botanical information

Adenium comprises 5 species, which are sometimes merged into a single one, Adenium obesum with 6 subspecies. Adenium obesum is the most widespread species in the wild and in cultivation. It crosses readily with Adenium multiflorum Klotzsch in cultivation, but the areas of natural distribution do not overlap. Adenium is closely related to Pachypodium and Nerium.

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Growth and development

The stem base of Adenium obesum becomes strongly thickened with age and sometimes spreads over rocks. In the wild the plant flowers during the first part of the dry season while leafless. Pollination is by insects with a long slender proboscis. The proboscis is inserted through one of the slits in the cone formed by the anthers and the pollen is placed on the stigma. When the proboscis is withdrawn, it is gummed by contact with the knob of the style and picks up fresh pollen from the anthers. Fruits mature 2–3 months after pollination. In cultivation in warm climates the plant can be semi-evergreen if kept warm and well-watered. Under such conditions plants undergo a short period of leaf-drop and dormancy in spring or early summer. They can also endure a drought or cold-induced dormancy of several months as occurs in the natural habitat. Under favourable conditions some clones flower for 2–4 months or even nearly year-round. Flowering stops when temperatures exceed 38°C. Plants grown from seed may flower within 1 year. Plants grown from cuttings also develop a thickened stem base and become indistinguishable from seed-grown plants.

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Ecology

Adenium obesum occurs in savanna, dry bushland or woodland, and wooded grassland up to 2100 m altitude, on rocky or sandy soil. In cultivation it requires full sunlight and warm temperatures with maximum temperatures preferably above 30°C. Although it originates from dry areas, it tolerates high air humidity well, which explains its popularity e.g. in Thailand and the Philippines. Branch tips are damaged at temperatures below 5°C and Adenium obesum cannot be grown in the open when temperatures are regularly close to 0°C. Waterlogging is not tolerated.

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Propagation and planting

As an ornamental Adenium obesum is propagated by seed, grafting or cuttings. Viability of seed from cultivated plants is sometimes poor because of pollination problems. Viable seed should be planted in a sandy free-draining medium after removal of the hairy tufts and treatment with a fungicide. It germinates within a week at temperatures of about 30°C. Seedlings are ready for transplanting within 1 month when they have developed 6 leaves. Tip-cuttings dipped in a rooting hormone, planted in a coarse rooting medium and well watered are most successful. Selected plants and valuable hybrids are often propagated by cleft grafting as this process is more reliable than propagation by cuttings, although it requires more skill. Grafting onto oleander (Nerium oleander L.) is possible and leads to rich flowering.

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Management

Adenium obesum thrives under conditions of ample rainfall or irrigation with temperatures above 27°C and in a perfectly draining soil. During cool weather it is prone to root rot and then requires drier soil. For fast growth fertilizer should be applied regularly.

Diseases and pests

Bacterial and fungal root and stem rot are the most common diseases in cultivation. Avoiding wet cool conditions is the best control strategy. Spider mites, scale insects and mealy bugs occasionally cause damage. Caution is needed when using pesticides as Adenium obesum is sensitive to many formulations containing oil. Diseases and pests seem rare in the wild.

Genetic resources and breeding

Adenium obesum occurs in a large area and does not seem to be in danger of genetic erosion.

Breeding

Many ornamental cultivars of Adenium obesum have been developed as well as hybrids with other species. Well known selections are ‘Singapore’ which is deep pink and probably originally from Yemen, ‘Red Everbloomer’, ‘Mombasa’ which is a much-branched dwarf, ‘Fritz Dederer’ forming thick corky white bark, and ‘Tom Grumbleys’ with purely white flowers. Hybrids between Adenium obesum and Adenium swazicum Stapf include ‘Asha’, ‘Endless Sunset’, ‘Perpetual Pink’ and ‘Volcanic Sunset’.

Prospects

The chemical and pharmacological properties of Adenium obesum deserve more research attention although there are no immediate prospects for the development of heart or cancer medicines. Interest in Adenium obesum as an ornamental is likely to remain strong because of the striking habit and flowers.

Major references

• Dimmitt, M.A. & Hanson, C., 1991. The genus Adenium in cultivation. Part 1: A. obesum and A. multiflorum. Cactus and Succulent Journal 63: 223–225.
• Leeuwenberg, A.J.M., 2003. Apocynaceae. In: Hedberg, I., Edwards, S. & Sileshi Nemomissa (Editors). Flora of Ethiopia and Eritrea. Volume 4, part 1. Apiaceae to Dipsacaceae. The National Herbarium, Addis Ababa University, Addis Ababa, Ethiopia and Department of Systematic Botany, Uppsala University, Uppsala, Sweden. pp. 87–98.
• Leeuwenberg, A.J.M., Kupicha, F.K., Barink, M.M., Beentje, H.J., de Kruif, A.P.M., Plaizier, A.C. & Zwetsloot, H.J.C., 1985. Apocynaceae. In: Launert, E. (Editor). Flora Zambesiaca. Volume 7, part 2. Flora Zambesiaca Managing Committee, London, United Kingdom. pp. 395–503.
• McLaughlin, J. & Garofalo, J., 2002. Desert Rose (Adenium obesum). Fact sheet 71. [Internet] Cooperative Extension Service, Miami-Dade County/University of Florida, Homestead, United States. 5 p. http://miami-dade.ifas.ufl.edu/pdfs/ ornamental/ornamental_publications/ desert-rose.PDF. Accessed July 2004.
• Neuwinger, H.D., 1996. African ethnobotany: poisons and drugs. Chapman & Hall, London, United Kingdom. 941 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.
• Plaizier, A.C., 1980. A revision of Adenium Roem. & Schult. and of Diplorhynchus Welw. ex Fic. and Hiern (Apocynaceae). Mededelingen Landbouwhogeschool Wageningen 80–12. Wageningen, Netherlands. 40 pp.
• Rowley, G.D., 1983. The Adenium and Pachypodium handbook. Smart & Co. Ltd., Brackley, United Kingdom. 95 pp.
• Yamauchi, T. & Abe, F., 1990. Cardiac glycosides and pregnanes from Adenium obesum (Studies on the constituents of Adenium 1). Chemical and Pharmaceutical Bulletin 38: 669–672.

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Other references

• Arbonnier, M., 2000. Arbres, arbustes et lianes des zones sèches d’Afrique de l’Ouest. CIRAD, MNHN, UICN. 541 pp.
• Cepleanu, F., Hamburger, M.O., Sordat, B., Msonthi, J.D., Gupta, M.P., Saadou, M. & Hostettmamm, K., 1994. Screening of tropical medicinal plants for molluscicidal, larvicidal, fungicidal and cytotoxic activities. International Journal of Pharmacognosy 32: 294–307.
• Eggli, U. (Editor), 2002. Illustrated handbook of succulent plants: Dicotyledons. Springer, Berlin, Germany. 554 pp.
• Forster, P.I., 1998. Correct names for some cultivated species of Adenium (Apocynaceae). Cactus and Succulent Journal 70(4): 199–200.
• Goyder, D., 2001. Is Adenium a valid genus? Asklepios 83: 3.
• Hargreaves, R., 2002. How many species of Adenium are there? Asklepios 85: 4–6.
• Melero, C.P., Medarde, M. & San Feliciano, A., 2000. A short review on cardiotonoc steroids and their aminoguanidine analogues. Molecules 5: 51–81.
• Mgbojikwe, L.O. & Okoye, Z.S.C., 2000. Acaricidal efficacy of the aqueous stem bark extract of Adenium obesum on the various life stages of cattle ticks. Nigerian Journal of Experimental and Applied Biology 2(1): 39–43.
• Neuwinger, H.D., 2000. African traditional medicine: a dictionary of plant use and applications. Medpharm Scientific, Stuttgart, Germany. 589 pp.
• Singh, C.U., 2004. Novel formulations of digitalis glycosides for treating cell-proliferative and other diseases. United States Patent Application 20040082521. U.S. Patent and Trademark Office, Alexandria VA, United States.
• Vethaviyasar, N. & John, D., 1982. 16-anhydro-3-acetyl-gitoxigenin in Adenum obesum. Planta Medica 44: 123–124.

Afriref references

Sources of illustration

• Plaizier, A.C., 1980. A revision of Adenium Roem. & Schult. and of Diplorhynchus Welw. ex Fic. and Hiern (Apocynaceae). Mededelingen Landbouwhogeschool Wageningen 80–12. Wageningen, Netherlands. 40 pp.

Author(s)

•	L.P.A. Oyen 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

•	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

Oyen, L.P.A., 2006. Adenium obesum (Forssk.) Roem. & Schult. [Internet] Record from PROTA4U. Schmelzer, G.H. & Gurib-Fakim, A. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands. <http://www.prota4u.org/search.asp>. Accessed .

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