Euphorbia tirucalli

L.

Family : Euphorbiaceae
Common names : pencil plant, rubber-hedge euphorbia (Eng.); kraalmelkbos (Afr.)

Euphorbia tirucalli

Euphorbia tirucalli has unmistakable, brush-like branch masses that are a noticeable feature of the plant. It also occurs over the widest distribution of all local euphorbias and is also a very variable plant ranging from many-branched shrubs to large trees, depending on the particular habitat.

Description
The rubber-hedge euphorbia is a many-branched, succulent plant, usually 3-5 m but may reach 10 m on occasion. The bark of very old specimens is grey and rough with longitudinal dents and ridges that break up into very small fragments. There are sometimes conspicuous, small protuberances, such as a bulge, knob, or swelling, on the bark, and occasionally black, rough, crosswise bands. The branches are cylindrical, smooth and glabrous-green, 5-8 mm in diameter, forming brush-like masses that are the best known feature of this species. Plants are without spines.

Bark

The leaves are small and slender, up to 12 x 1.5 mm, rarely seen, as they fall very early. Leaf scars on young twigs form conspicuous dents which contract until they are no more than grey dots on older branchlets and can even be seen on fairly thick green stems. The thin twigs are pendant (hanging down), pale green and occur opposite each other, alternate or in groups on the branchlets which gives a rather untidy and rounded appearance to the crowns.

The flowers are yellow, inconspicuous, and carried in clusters at the apex of the short branches or in the angles of branches. They appear in September to December.

Flowers

Fruits are tripartite capsules (divided into three parts), about 12 mm in diameter, longitudinally very slightly lobed, short-stalked (8 mm), pale green, with a pink tinge and conspicuously pubescent (clothed with soft hairs). As with other members, the capsules dehisce while still on the tree. The fruits appear from November to December. Generally the stalks are bent at an angle.

Fruits

The seeds are oval, about 4 x 3 mm, glabrous, smooth and dark brown with a white line around the small white caruncle (fleshy wart near the hilum of the seed). This spineless species contains large quantities of latex which is freely exuded by the twigs and branchlets at the slightest injury.

Conservation status
Euphorbia tirucalli is abundant in southern Africa and seeds itself freely across its distribution range. It is well represented in various habitats and is not an endangered species.

Distribution and habitat
There are more than 2000 species of Euphorbia found in the warmer parts of the world. From approximately 200 species found in South Africa, 14 can be seen as trees. These succulent trees resemble cactus plants and at first glance are often mistaken for cacti.

The rubber-hedge euphorbia has its southernmost distribution in the Eastern Cape and at its northernmost in Ethiopia. It is therefore present in all the warmer parts of South Africa and is particularly abundant in KwaZulu-Natal, where sometimes pure stands can be observed. Outside Africa it also occurs in India, Indonesia, China and the Philippine Islands.

Euphorbia tirucalli occurs in various habitats ranging from grassy hills, rocky outcrops and ridges, along river courses, bushveld and open savanna. The associated geology varies from granite, sandstone and rhyolite. Dense thickets are associated with this species and the plant itself may form hedge-like barriers in the veld.

Derivation of name and historical aspects
The family name Euphorbiaceae and genus name Euphorbia were named in honour of a Linnaean hero namely Euphorbus, first century physician to King Juba of Mauritania. He is believed to have used plants of this genus as medicine. The species name tirucalli was given by Linnaeus in 1753 as this was the name used by the natives of Malabar, a region of southern India. The rubber-hedge has been so widely cultivated that it is now difficult to say where it occurs naturally and where it has been introduced. Early traders and sailors carried plants from South Africa to India and the Far East, and the fact that these have all flourished, gives us some idea of the incredible resilience of the plant.

Ecology
Euphorbia tirucalli produces yellowish flowers that attract butterflies, bees and other insects. These are primarily responsible for pollination as the flowers also produces minute quantities of nectar. The seeds are also eaten by various birds. The plant itself has very bushy branches which are used for nesting and roosting and the spineless branches are an added advantage to the birds.

Bird perching on branch

The plants are drought resistant and very resilient, which is why it has become popular in cultivation. It uses its green stems to photosynthesize and is therefore able to minimize surface exposure and water loss. As far as can be established, there have been no recordings of animals that eat the branches of E. tirucalli. It is possible that the poisonous latex that the plant produces may act as a deterrent to browsers.

Uses and cultural aspects
The common name rubber-hedge refers to its widespread use as planted hedges around smallholdings, habitations and livestock pens. In this way mosquitoes and other intruders can be kept out. The latex, as in other euphorbias, is very toxic and may cause blindness, blisters on the skin, and even prove fatal if enough of it is swallowed. There is at least one recorded case of it causing death from gastro-intestinal haemorrhage. In traditional medicine it is regarded as a cure for sexual impotence and an antidote for snakebite. The use of various euphorbias including E. tirucalli as a fish poison is also well documented.

It was once thought to be a species that could yield true rubber but numerous experiments have shown that the latex contains a too high percentage of resin. The plant as a whole contains 0.4 % rubber and 5.1 % latex. Products manufactured from the rubber were of a low quality. Efforts to use the resin in the manufacture of varnish were also doomed to failure as the product was not durable. The timber of E. tirucallis is white and harder than most related species but it is not put to use in South Africa. As it is not attacked by borers, it is used elsewhere as struts for roofs.

Tree at Kirstenbosch

Growing Euphorbia tirucalli

Euphorbia tirucalli grows moderately fast and thrives in moderate to warm climates. It does not seem to cope with extreme cold. Plants can easily be cultivated by means of seeds, cuttings or truncheons. A coarse sandy medium is ideal for sowing the seeds.

Fresh seeds must be sown in late summer from February to March and kept in a warm, moist area. Plants prefer to have their 'feet' dry especially in winter. Young plants grow relatively fast and will benefit from liquid fertilizers and well-composted, well-drained soils. These beautiful trees are best positioned in open, full sun positions on rocky situations such as a rock garden, embankment or gravelly slopes. They make very good specimens in dry karoo gardens provided that the winters aren't too cold. Other euphorbias that best compliment E. tirucallis include E. ingens, E. cooperi, E. triangularis, E. grandicornis, E. tetragona and E. grandidens. For the best garden display, it is advisable to cultivate a combination of large, medium and small succulent plants such as Aloe, Crassula, Cotyledon, Tylecodon and Cyphostemma, while using colourful annuals and perennials in amongst the permanent specimens.

References and further reading

  • Coates Palgrave, K. 2002. Trees of southern Africa. Struik, Cape Town.
  • Germishuizen, G. & Meyer, N.L. (eds). 2003. Plants of southern Africa : an annotated checklist. Strelitzia 14. National Botanical Institute, Pretoria.
  • Jackson, W.P.U. 1990. Origins and meanings of South African plant genera. University of Cape Town Ecolab.
  • Leistner, O.A. 2005. Seed plants of southern tropical Africa : families and genera. Southern African Botanical Diversity Network Report No. 26. SABONET, Pretoria.
  • Smith, C.A. 1966. Common names of South African plants. Memoirs of the Botanical Survey of South Africa No. 35.
  • Stearn, W.T. 2003. Stearn's dictionary of plant names for the gardener. Cassel, UK.
  • Van Wyk, B-E. & Gericke, N. 2000. People's plants. A guide to useful plants of southern Africa. Briza Publications, Pretoria.
  • Van Wyk, P. 1974. Trees of the Kruger National Park, vol. 2. Purnell, Johannesburg.

 

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