Euphorbia (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Euphorbia L.

Protologue: Sp. pl. 1: 450 (1753); Gen. pl. ed. 5: 208 (1754).

Family: Euphorbiaceae

Chromosome number: x= 9, 10, 11; E. antiquorum: 2n= 60, E. barnhartii: 2n= 40, E. heterophylla: 2n= 54, 56, E. hirta: n= 8, 9, 10, E. neriifolia: 2n= 60, 80, 90, 180, E. prostrata: n= 9, 2n= 20, E. thymifolia: n= 9, E. tirucalli: 2n= 20

Major species

• Euphorbia antiquorum L.,
• E. hirta L.,
• E. thymifolia L.

Vernacular names

• Spurge (En).
• Euphorbe (Fr).

Origin and geographic distribution

Euphorbia comprises over 2000 species and occurs worldwide, though most species are found in tropical, subtropical and warm temperate regions. There are 35 species native to South-East Asia: Vietnam has 24 species, Thailand 25, Sumatra 6, Java 5, Borneo 5, the Philippines 6, Sulawesi 5, the Lesser Sunda Islands 11, the Moluccas 7 and New Guinea 15. Australia has 45 species.

Uses

The latex of many Euphorbia species is used medicinally as a purgative, has antidiarrhoeal and antibacterial properties, and is used to treat boils, warts, wounds and other skin disorders. It is also often used as a fish poison and has insecticidal and fungicidal properties. The woody central part of the stem of some succulent species is applied as a remedy for dysentery. The leaves of several Euphorbia species are used to treat asthma. Traditional pharmacies often include material from several Euphorbia species.

Some species are cultivated as ornamentals or living fences. The latex of some species can be converted into fuel and has been investigated as a possible energy source.

Properties

Phytochemical investigations of the lipophilic constituents of E. tirucalli has revealed the presence of steroids (sitosterol, stigmasterol, campesterol) and fatty acids (palmitic acid, linoleic acid).

A lectin isolated from the latex of E. neriifolia agglutinated trypsinized human and rabbit erythrocytes. Untreated sheep erythrocytes did not agglutinate, but sialidase-treated sheep erythrocytes did. Galactose and sugars containing galactose inhibited the haemagglutination with increased β-anomeric specificity. The lectin possesses mitogenic activity with murine spleen lymphocytes but it does not inhibit protein synthesis in the rabbit reticulocyte lysate assay. The lyophilized aqueous extract of E. hirta has central analgesic properties. A dose of 20 mg/kg produced action against chemical stimuli, whereas one of 25 mg/kg produced action against thermic stimuli; the effects were inhibited by a pretreatment with naxolene, a specific morphinic antagonist compound. At the sedative doses of 100 and 400 mg/kg an antipyretic activity was obtained on the yeast-induced hyperthermia model. Significant and dose-dependent anti-inflammatory effects were also observed on an acute inflammatory process in a carrageenin-induced oedema test in rats from a dose of 100 mg/kg.

The ethyl acetate fraction of the ethanol extract of E. prostrata administered orally to rats at 200 mg/kg inhibited 76% of acute carrageenin-induced paw oedema. The ethyl acetate extract and a fraction (KSE-23) isolated chromatographically from it, showed significant anti-inflammatory activity when applied topically in a murine model of carrageenin-induced footpad oedema in mice. KSE-23 was found to be more potent than indomethacin given by the same route.

The extracts of E. tirucalli have markedly enhancing effects on the activation of latent Epstein-Barr virus (EBV) genomes in the EBV carrying lymphoblastoid cells and also on EBV-induced transformation of human lymphocytes. Soil and drinking water taken around the plants have the same enhancing effects and are a serious risk to humans in Africa. Various doses of powdered E. prostrata administered orally to male albino rabbits produced significant hypoglycaemic effects in normal rabbits, but had no effect in alloxan-diabetic rabbits. The methanol extract also decreased the blood glucose of normal rabbits. The methanol extract of E. hirta was effective against dysentery-causing Shigella spp. using the vero cell line, and it had no cytotoxic effects. This is attributable to quercitrin, a flavonoid, isolated from a lyophilized decoction of E. hirta. At doses of 50 mg/kg quercitrin is known to show preventive activity against diarrhoea induced by castor oil and prostaglandin E2 in mice, but not when magnesium sulphate is used as a cathartic agent. The aqueous extract of E. hirta has been found to strongly reduce the release of prostaglandins. Additionally, the extracts exerted an inhibitory effect on platelet aggregation. In organ bath tests with ileum preparations shikimic acid and choline extracted from the aerial parts of E. hirta had relaxing and contracting properties, respectively. The methanol extract of leaves and stems of E. hirta inhibited the activity of angiotensin-converting enzyme by 90% at 500 μg and 50% at 160 μg. The effect of the extract on thirst was examined in Wistar rats. The extract (10 mg/100 g, intraperitoneally) significantly decreased the amount of water the rats consumed. Extracts of whole plant material are also reported to have oestrogenic activity. Extracts of E. hirta showed anti-microbial activity against Candida albicans, Escherichia coli, and Staphylococcus aureus. Leaf extracts of E. hirta severely inhibited sporulation in the hyphomycete Helminthosporium sp. Finally, drying E. hirta prior to extraction considerably reduces the cytotoxic activity of certain of its extracts.

The latex of Euphorbia is often highly irritant to the eyes and must be washed away immediately. It can cause irritation and vesication from contact and emesis and purgation from ingestion. These effects are caused by a large number of different esters of the tetracyclic diterpenoid phorbol, many of which have also been shown to act as tumour promoters (cocarcinogens). The latex of E. tirucalli contains the irritant and/or cocarcinogenic constituents ingenane and tigliane-type diterpene esters derived from the parent alcohols ingenol, phorbol and resiniferonol. Furthermore, the latex is an emulsion of about 30% terpenes in water.

The latex hydrocarbon is largely a C₃₀ triterpenoid which can be cracked to make high octane gasoline. The gross energy value of E. tirucalli biomass is 17 600 kJ/kg. Biomass can be converted into gas, liquid fuels and solid fuels such as pellets, briquettes and charcoal.

Rubber production from the latex of E. tirucalli was investigated early in the 20th Century, but continuous latex production proved difficult and its high resin content limited the profitability of the rubber production.

Description

• Monoecious or rarely dioecious, annual, biennial or perennial herbs, shrubs or trees, sometimes succulent, armed or unarmed, with latex.
• Leaves alternate, opposite or verticillate, sometimes much reduced, simple, uniform or heterophyllous, margin entire, toothed or lobed; stipules present or absent, sometimes modified into spines.
• Flowers unisexual, one female flower together with several male flowers enclosed within a small, cupuliform, glanduliferous involucre, the whole structure termed a "cyathium", functioning as a single, bisexual flower; cyathia solitary or combined into corymbs or cymes, occasionally unisexual; bracteoles usually ligulate and fringed.
• Male flowers reduced to single stamens; anthers with 2 cells.
• Female flowers pedicellate, reduced to single pistils or with a minute perianth; ovary superior, during maturation on an accrescent pedicel and often nodding outside the cyathial cup, 3-locular with 1 ovule per locule, styles 3, partly fused, entire to 2-fid.
• Fruit a smooth to tuberculate, sometimes fleshy capsule, splitting open elastically, first dehiscing septicidally and then loculicidally.
• Seeds with endosperm, with or without caruncle.
• Seedling with epigeal germination; cotyledons leafy, usually elliptical to ovate, glabrous; hypocotyl elongated, glabrous, epicotyl absent or very short; first two leaves opposite.

Growth and development

In Java, E. atoto, E. hirta, E. prostrata and E. thymifolia flower throughout the year, E. barnhartii usually in September-November, whereas E. tirucalli rarely flowers in October but never sets fruit. In most Euphorbia the capsules dehisce with force and ejaculate their seeds which are thus dispersed over some distance. Ants may act as a dispersal agent of some Euphorbia, for example in E. hirta and E. heterophylla. E. hirta produces up to 3000 seeds per plant which show a high germination rate. E. tirucalli is one of the very few known plants combining a Crassulacean acid metabolism (CAM) pathway of its branches and twigs with the C₃ metabolism pathway of its leaves. Consequently it is very drought-resistant and very efficient in photosynthesis.

Other botanical information

Some authors have separated Euphorbia into a number of distinct genera, usually based upon peculiarities of the cyathial structure. Others recognize these entities at infrageneric level. In South-East Asian and Australian literature one may, for example encounter the genus Chamaesyce next to Euphorbia; here, however, Chamaesyce is regarded as a subgenus.

Some of the American Euphorbia species that have been introduced into South-East Asia are sometimes referred to as members of the genus Poinsettia, or of the subgenus Poinsettia. All tree-like, succulent, spinose species belong to the subgenus Euphorbia. E. cyathophora and E. heterophylla are now regarded as two distinct species, but have not been treated as such in older literature. Therefore much of the older information cannot be referred to either of these species. Both species are strikingly variable in leaf shape. E. buxoides Radcl.-Sm., which closely resembles E. plumerioides, is widely planted as a hedge and boundary marker in the highlands throughout New Guinea. Its bark is chewed to induce vomiting and acts as a poison antidote. Leaves of E. vachellii Hook. & Arn. (syn. E. serrulata Reinw. ex Blume non Thuill.) are used internally to treat catarrh in Papua New Guinea.

Ecology

The succulent, spinose Euphorbia species generally occur in dry places, on rocky or sandy soils, occasionally in dry forest. Most herbaceous Euphorbia species are commonly found in waste places and as a weed in fields and gardens.

Propagation and planting

The weedy medicinal Euphorbia species produce seed in abundance and reproduce spontaneously. E. tirucalli can easily be propagated by stem cuttings, which greatly facilitates its planting as a hedge. Cuttings can best be taken from older branches; they are left to dry for 1 day before planting. A density of 10 000-20 000 plants/ha is normal when grown as fuel crop.

In vitro production of active compounds

Isolation and culturing of protoplasts of E. tirucalli has been successful. Callus tissue of E. tirucalli produces the 4,4'-dimethyl sterols euphol and tirucallol. Euphol is the principal terpene in the latex of the plant, whereas tirucallol is found in intact parental tissue. The highest yield of sterol has been obtained on a Murashige and Skoog medium supplemented by indole acetic acid (IAA) and kinetin; incorporation of squalene at 1.0 mg/l enhanced sterol production.

Husbandry

The herbaceous medicinal Euphorbia species are in general weeds. E. heterophylla is a shade-tolerant, pantropical weed and as such its control is more important than its husbandry. It may be troublesome in crops like maize, cotton, cowpea and soya bean. Crops need to be kept free from E. heterophylla, especially in the early phases of development. Well-established E. heterophylla can depress yields greatly, for instance by as much as 75% in cowpea. Fresh E. heterophylla seed germinates readily under tropical conditions, but remains dormant under temperate circumstances and then both light and temperature influence dormancy breaking. E. prostrata shows strong allelopathic effects on a number of crops. Its aqueous extract, decaying residues and root exudates have been found to be inhibitory to several species. Under semi-arid conditions the regrowth of coppice of E. tirucalli is excellent.

Harvesting

In general stems or whole plants of herbaceous Euphorbia are harvested to be used fresh. E. tirucalli can be coppiced at 20-30 cm height.

Yield

When planted at a spacing of 1 m × 1 m E. tirucalli in Thailand produced 120 t/ha fresh material and 14 t/ha dry matter after 1 year, yielding 40-88 kg of crude oil, 135-213 kg of sugar and 1.8 t of bagasse. After 1.5 years with 6 trimmings a year, 148 t/ha of biomass (i.e. 17.5 t dry weight) could be harvested. It was calculated in Japan that 1-2 t of crude oil could be obtained per ha per year from E. tirucalli. A daily production of biogas from E. tirucalli of about 31 m³/ha (226 l/kg dry matter) is considered possible based on an annual production of 500 t biomass/ha by means of a two-phase methane fermentation process; a one-phase process yields 175-323 l of biogas per kg dry matter.

Genetic resources and breeding

Given the common and widespread occurrence of most medicinal Euphorbia species and their weedy nature, the risk of genetic erosion appears very limited. The same holds for the succulent Euphorbia species planted as ornamentals. Neither germplasm collections nor breeding programmes are known of.

Prospects

Phorbols and phorbol-esters are extremely harmful to the skin and mucous membranes, and also reported to be tumour promoters. Therefore, the medicinal prospects of many Euphorbia species are very limited. Acetylated esters of phorbols, however, may play a role in the search for possible anti-tumour compounds.

E. tirucalli may hold promise for energy production through biomass utilization or use of the crude oil extracted from the plants.

Literature

• Calvin, M., 1987. Fuel oils from euphorbs and other plants. Botanical Journal of the Linnean Society 94: 97-110.
• Galvez, J., Crespo, M.E., Jimenez, J., Suarez, A. & Zaruelo, A., 1993. Antidiarrhoeic activity of quercitrin in mice and rats. Journal of Pharmacy and Pharmacology 45(2): 157-159.
• Hiermann, A. & Bucar, F., 1994. Influence of some traditional medicinal plants of Senegal on prostaglandin biosynthesis. Journal of Ethnopharmacology 42(2): 111-116.
• Jantarawaratit, S., Reutrakul, V. & Ratanabanangkoon, K., 1997. Estrogenic activity found in the herb Euphorbia hirta (nam nom rat chasee). Mahidol University Annual Abstracts 192.
• Lanhers, M.C., Fleurentin, J., Dorfman, P., Mortier, F. & Pelt, J.M., 1991. Analgesic, antipyretic and anti-inflammatory properties of Euphorbia hirta. Planta Medica 57(3): 225-231.
• Mizuno, F. et al., 1986. Epstein-Barr virus-enhancing plant promoters in East Africa. AIDS Research 2. Supplement 1: S151-S155.
• Nguyen Nghia Thin, 1989. Useful plants of Euphorbiaceae in the flora of Vietnam. Forestry Revue, Hanoi 1989: 29-30.
• Shingla, A.K. & Pathak, K., 1990. Topical antiinflammatory effects of Euphorbia prostrata on carrageenan-induced footpad oedema in mice. Journal of Ethnopharmacology 29(3): 291-294.
• Van Damme, P., 1989. Studie van Euphorbia tirucalli L., morfologie, fysiologie, teeltvoorwaarden [Study of Euphorbia tirucalli L., morphology, physiology, agronomy]. Thesis, Gent University, Belgium. 375 pp. + appendices.
• Wilson, A.K., 1981. Euphorbia heterophylla: a review of distribution, importance and control. Tropical Pest Management 27: 32-38.

Selection of species

• Euphorbia antiquorum
• Euphorbia atoto
• Euphorbia barnhartii
• Euphorbia cyathophora
• Euphorbia heterophylla
• Euphorbia hirta
• Euphorbia neriifolia
• Euphorbia plumerioides
• Euphorbia prostrata
• Euphorbia synadenium
• Euphorbia thymifolia
• Euphorbia tirucalli

Authors

• Nguyen Nghia Thin & M.S.M. Sosef