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Euphorbia unispina N.E.Br.

Protologue
Dyer, Fl. trop. Afr. 6(1): 561 (1911).
Family
Euphorbiaceae
Vernacular names
Candle plant (En).
Origin and geographic distribution
Euphorbia unispina occurs from Guinea and Mali east to southern Sudan.
Uses
The latex of Euphorbia unispina is very caustic and toxic, and very irritating to the skin and mucous membranes. It can cause blindness when in contact with eyes. Despite its toxicity, it is medicinally used. In Guinea, Mali and Côte d’Ivoire the latex is applied to the neck to cure sleeping sickness, because it is believed that the disease is caused by ganglia in the neck. In Côte d’Ivoire and Nigeria the latex is applied to leprosy sores. Two drops of latex on an egg are eaten as an anthelmintic. In Benin stem ash is inhaled to treat asthma; palm oil with latex is taken to treat constipation and colic; a macerate of the cut stems in water is applied to skin diseases and haemorrhoids. In northern Nigeria the latex is rubbed onto the body to treat mental illness. In Cameroon the latex is placed in a carious tooth to relieve toothache or to help to loosen the tooth and render extraction easier. Dried leaves are smoked in a pipe to treat bronchitis.
In addition to medicinal uses, the latex is widely used in the preparation of arrow poison, though always mixed with other ingredients, such as seeds of Strophanthus species. It is also used in fish poison and animal traps. In northern Nigeria the latex is reported to be used as a poison to commit murder and suicide. The latex is applied to scarifications to thicken them. In West Africa Euphorbia unispina is sometimes planted in gardens as an ornamental plant or as a hedge around fields and graveyards. In Europe and the United States it is a rare pot plant in succulent collections.
Euphorbia unispina closely resembles Euphorbia poissonii Pax, and they have similar uses.
Production and international trade
Some compounds isolated from Euphorbia unispina are sold on the internet. Resiniferatoxin was sold in 2007 for US$ 35 (1 mg) to US$ 525 (25 mg); tinyatoxin was sold for US$ 60 (1 mg) to US$ 240 (5 mg). Euphorbia unispina is also traded on the internet as an ornamental plant.
Properties
The latex of Euphorbia unispina contains esters of diterpene alcohols of the tigliane type, 12-deoxyphorbol and 12-deoxy-16-hydroxyphorbol, and the daphnane type, resiniferonol, as well as several macrocyclic esters of the diterpene alcohol 18-hydroxyingol. Daphnane esters are generally known for their potent skin irritant properties whereas tigliane esters are toxic and tumour promoters; some tigliane esters, however, possess anticancer activities.
Euphorbia unispina contains a smaller variety of chemical compounds than Euphorbia poissonii and also in lower concentrations. This is reflected by the irritant activity of the latex, which is more than 30 times less than in Euphorbia poissonii latex, although after 24 hours both activities have almost the same value. The isolated aromatic esters of the daphnane type are more potent irritants in mouse ear tests than the aromatic tigliane esters, especially resiniferatoxin (ID50 = 0.00021 nMol / 5 μg) and tinyatoxin (ID50 = 0.0012 nMol / 5 μg), whereas proresiniferatoxin is almost inactive. The isolated aromatic tigliane esters, candletoxin A (ID50 = 0.48 nMol / 5 μg) and candletoxin B (ID50 = 0.19 nMol / 5 μg), as well as DPP (12-deoxyphorbol 13-phenylacetate; ID50 = 0.064 nMol / 5 μg) were also strongly irritant. The major compound isolated from Euphorbia poissonii, the highly irritant 12-deoxyphorbol-13-O-phenylacetate-20-O-acetate, was not isolated from Euphorbia unispina. The irritant activity of resiniferatoxin and tinyatoxin is rapid and reaches a maximum within 4 hours and then fades to inactivity after 24 hours. Resiniferatoxin is highly toxic, as it binds to pain receptors in the same way as capsaicin but much more powerfully. It stimulates the neurons to fire repeatedly until the neuron dies, causing searing pain and sending the victim into severe anaphylactic shock. It is used in the treatment of incontinence associated with an overactive bladder. It also has antifeedant and analgesic properties. Efforts are being made to synthesize this compound, as it will be of use in the elucidation of the binding characteristics of resiniferatoxin to its receptor sites.
Botany
Monoecious, candelabriform, sparsely branching shrub up to 3.5 m tall; branches cylindrical, up to 2.5 cm in diameter, silvery grey, covered with shallow tubercles and horny spine shields up to 1 cm in diameter, grey, with 1 spine, with white latex. Leaves arranged spirally at stem apex in 4–5 ranks, simple, soon falling; stipules modified into 2 stout spines 6–10 mm long; petiole short, thick; blade oblong to spoon-shaped, 5–12 cm × 1.5–5 cm, base long-cuneate, apex notched and fringed, acute or rounded, almost entire, fleshy, glabrous, pinnately veined. Inflorescence an axillary cyme at the ends of branches, consisting of clusters of flowers, each cluster called a ‘cyathium’; peduncle short; cyme branches c. 2, short; bracts 2, ovate, c. 2 mm long, membranaceous; cyathia c. 4 mm in diameter, with a shortly funnel-shaped involucre, green, 5-lobed with broadly ovate, fringed lobes, glands 5, elliptical, touching, red, each cyathium containing 1 female flower surrounded by many male flowers. Flowers unisexual; male flowers sessile, perianth absent, stamen shortly exserted, red; female flowers with curved pedicel 4–8 mm long in fruit, perianth 5-lobed, ovary superior, 3-celled, glabrous, styles 3, up to 2 mm long, slender, fused at base, bifid at apex. Fruit an obtusely 3-lobed capsule c. 6 mm in diameter, glabrous, 3-seeded. Seeds ovoid.
Euphorbia comprises about 2000 species and has a worldwide distribution, with at least 750 species occurring in continental Africa and about 150 species in Madagascar and the Indian Ocean islands. Euphorbia unispina belongs to subgenus Euphorbia, section Euphorbia, a large group which is characterized by succulent, angular stems, stipules modified into small spines, a spine shield with a pair of spines (sometimes fused into a single spine), axillary inflorescences and seeds without caruncle. Plants of Euphorbia poissonii Pax having small spines resemble Euphorbia unispina closely. The former may be distinguished from Euphorbia unispina by the stouter flowering branches, with leaves in 8–10 ranks instead of 4–5, by the usually rudimentary spines, and by the numerous inflorescences densely clustered at the end of the shoots.
Euphorbia unispina flowers at the end of the dry season, before new leaves are formed.
Several other Euphorbia species closely related to Euphorbia unispina have medicinal uses.
Euphorbia meridionalis P.R.O.Bally & S.Carter occurs in Kenya and Tanzania; in Kenya the Maasai people drink water or soup in which slices of stem are boiled, to induce diarrhoea to treat malaria and venereal diseases. Euphorbia schizacantha Pax occurs in Ethiopia, Somalia and northern Kenya, and in Somalia the crushed plant is applied to the anus to treat haemorrhoids. In Ethiopia a root infusion is drunk to treat cough. Euphorbia schizacantha is sought after by plant collectors because of its drooping branches and because the fusion of the 2 main spines is not complete, thus having a forked tip. Euphorbia venenifica Tremaux ex Kotschy occurs in Chad, Sudan, Ethiopia and Uganda. The latex is very caustic and toxic, and in southern Sudan it is part of an arrow poison. In southern Chad and southern Sudan the latex is also used as fish poison.
Ecology
Euphorbia unispina occurs on rocky hills and slopes in savanna. It is locally common.
Management
Euphorbia unispina is easily propagated by stem cuttings; these should be at least 20 cm long, preferably cut at the base of a branch where the cut surface will be woody. After cutting they should be allowed to lie in a shaded place for at least 2 weeks for a callus to form on the cut end. Euphorbia unispina can also be grown from seed. Euphorbia unispina latex is usually harvested from wild plants or from those planted near villages. Harvesting of the leaves is seasonal because the plants are leafless in the dry season.
Genetic resources and breeding
Euphorbia unispina is locally common and probably not threatened by genetic erosion. As a (semi-)succulent Euphorbia species, its trade is controlled under CITES appendix 2.
Prospects
Although Euphorbia unispina has useful biological activities, its use for medicinal purposes is limited by the toxicity of the latex. However, the prospects of some of its compounds are good; for example, resiniferatoxin is going through phase 2 clinical trials and DPP can be used in the therapy of persistent HIV-1 infection. The taxonomy and distribution areas of Euphorbia unispina, Euphorbia poissonii and Euphorbia venenifica need to be reviewed as these species resemble each other closely.
Major references
• Asres, K., Seyoum, A., Veeresham, C., Bucar, F. & Gibbons, S., 2005. Naturally derived anti-HIV agents - review article. Phytotherapy Research 19: 557–581.
• Burkill, H.M., 1994. The useful plants of West Tropical Africa. 2nd Edition. Volume 2, Families E–I. Royal Botanic Gardens, Kew, Richmond, United Kingdom. 636 pp.
• Eggli, U. (Editor), 2002. Illustrated handbook of succulent plants: Dicotyledons. Springer, Berlin, Germany. 554 pp.
• Keay, R.W.J., 1958. Euphorbiaceae. In: Keay, R.W.J. (Editor). Flora of West Tropical Africa. Volume 1, part 2. 2nd Edition. Crown Agents for Oversea Governments and Administrations, London, United Kingdom. pp. 364–423.
• Neuwinger, H.D., 1996. African ethnobotany: poisons and drugs. Chapman & Hall, London, United Kingdom. 941 pp.
Other references
• Adjanohoun, E.J., Adjakidjè, V., Ahyi, M.R.A., Aké Assi, L., Akoègninou, A., d’Almeida, J., Apovo, F., Boukef, K., Chadare, M., Cusset, G., Dramane, K., Eyme, J., Gassita, J.N., Gbaguidi, N., Goudote, E., Guinko, S., Houngnon, P., Lo, I., Keita, A., Kiniffo, H.V., Kone-Bamba, D., Musampa Nseyya, A., Saadou, M., Sodogandji, T., De Souza, S., Tchabi, A., Zinsou Dossa, C. & Zohoun, T., 1989. Contribution aux études ethnobotaniques et floristiques en République Populaire du Bénin. Agence de Coopération Culturelle et Technique, Paris, France. 895 pp.
• Evans, F.J. & Kinghorn, A.D., 1977. A comparative phytochemical study of the diterpenes of some species of the genera Euphorbia and Elaeophorbia. Botanical Journal of the Linnean Society 74: 23–35.
• Evans, F.J. & Schmidt, R.J., 1977. The succulent euphorbias of Nigeria. 2. Aliphatic diterpene esters of the lattices of Euphorbia poissonii Pax and E. unispina. Lloydia 40: 225–229.
• Gemedo-Dalle, T., Maass, B.L. & Isselstein, J., 2005. Plant biodiversity and ethnobotany of Borana pastoralists in southern Oromia, Ethiopia. Economic Botany 59(1): 43–65.
• Kiringe, J.W., 2006. A survey of traditional health remedies used by the Maasai of southern Kaijiado District, Kenya. Ethnobotany Research & Applications 4: 61–74.
• Neuwinger, H.D., 1996. African ethnobotany: poisons and drugs. Chapman & Hall, London, United Kingdom. 941 pp.
• Newton, L.E., 1992. An annotated and illustrated checklist of the succulent euphorbias of West tropical Africa. Euphorbia Journal 8: 112–122.
• Rauh, W., Loffler, E. & Uhlarz, H., 1969. Observations on some euphorbias from tropical West-Africa. Cactus & Succulent Journal 41: 210–220.
• Samuelsson, G., Farah, M.H., Claeson, P., Hagos, M., Thulin, M., Hedberg, O., Warfa, A.M., Hassan, A.O., Elmi, A.H., Abdurahman, A.D., Elmi, A.S., Abdi, Y.A. & Alin, M.H., 1992. Inventory of plants used in traditional medicine in Somalia. 2. Plants of the families Combretaceae to Labiatae. Journal of Ethnopharmacology 37: 47–70.
• Stäuble, N., 1986. Etude ethnobotanique des Euphorbiacées d’Afrique de l’Ouest. Journal of Ethnopharmacology 16: 23–103.
Author(s)
L.E. Newton
Department of Biological Sciences, Kenyatta University, P.O. Box 43844, Nairobi 00100, Kenya


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:
Newton, L.E., 2008. Euphorbia unispina N.E.Br. In: Schmelzer, G.H. & Gurib-Fakim, A. (Editors). Prota 11(1): Medicinal plants/Plantes médicinales 1. [CD-Rom]. PROTA, Wageningen, Netherlands.
leafy branch