Monday, June 14, 2010

Further of Euphorbia

The plants are annual or perennial herbs, woody shrubs or trees with a caustic, poisonous milky sap (latex). The roots are fine or thick and fleshy or tuberous. Many species are more or less succulent, thorny or unarmed. The main stem and mostly also the side arms of the succulent species are thick and fleshy, 15–91 cm (6–36 inches) tall. The deciduous leaves are opposite, alternate or in whorls. In succulent species the leaves are mostly small and short-lived. The stipules are mostly small, partly transformed into spines or glands, or missing.
Like all members of the family Euphorbiaceae, all spurges have unisexual flowers. In Euphorbia these are greatly reduced and grouped into pseudanthia called cyathia. The majority of species are monoecious (bearing male and female flowers on the same plant), although some are dioecious with male and female flowers occurring on different plants. It is not unusual for the central cyathia of a cyme to be purely male, and for lateral cyathia to carry both sexes. Sometimes young plants or those growing under unfavourable conditions are male only, and only produce female flowers in the cyathia with maturity or as growing conditions improve. The bracts are often leaf-like, sometimes brightly coloured and attractive, sometimes reduced to tiny scales. The fruits are three (rarely two) compartment capsules, sometimes fleshy but almost always ripening to a woody container that then splits open (explosively, see explosive dehiscence). The seeds are 4-angled, oval or spherical, and in some species have a caruncle.

Xerophytes and succulents
In the genus Euphorbia, succulence in the species has often evolved divergently and to differing degrees. Sometimes it is difficult to decide, and it is a question of interpretation, whether or not a species is really succulent or "only" xerophytic. In some cases, especially with geophytes, plants closely related to the succulents are normal herbs. About 850 species are succulent in the strictest sense. If one includes slightly succulent and xerophytic species, this figure rises to about 1000, representing about 45% of all Euphorbia species.

The latex (milky sap) of spurges acts as a deterrent for herbivores as well as a wound healer. Usually it is white, but in rare cases (e.g. E. abdelkuri) yellow. As it is under pressure, it runs out from the slightest wound and congeals within a few minutes of contact with the air. Among the component parts are many di- or tri-terpen esters, which can vary in composition according to species, and in some cases the variant may be typical of that species. The terpen ester composition determines how caustic and irritating to the skin it is. In contact with mucous membranes (eyes, nose, mouth) the latex can produce extremely painful inflammation. In experiments with animals it was found that the terpen ester resiniferatoxin had an irritating effect 10,000 to 100,000 times stronger than capsaicin, the "hot" substance found in chili peppers. Several terpen esters are also known to be carcinogenic.
Therefore spurges should be handled with caution. Latex coming in contact with the skin should be washed off immediately and thoroughly. Partially or completely congealed latex is often no longer soluble in water, but can be removed with an emulsion (milk, hand-cream). A physician should be consulted regarding any inflammation of a mucous membrane, especially the eyes, as severe eye damage including possible permanent blindness may result from acute exposure to the sap. It has been noticed, when cutting large succulent spurges in a greenhouse, that vapours from the latex spread and can cause severe irritation to the eyes and air passages several metres away. Precautions, including sufficient ventilation, are required. Small children and domestic pets should be kept from contact with spurges.

See Also: flora, online flowers, flower arrangement

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