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Encyclopedia Britannica - Main :: EUD-FAT |
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EUPHORBIACEAE , in botany, a large natural order of flowering plants, containing more than 220 genera with about ' See Dr Schafhf.utl's article on Musical Instruments
4000 species, chiefly tropical, but spreading over the whole earth with the exception of the arctic and cold alpine zones. They are represented in Britain by the spurges (Euphorbia, q.v.) (fig.') and dog's mercury (Mercurialis) (fig. 2), which are herba- ceous plants, but the greater number are woody plants and often trees. The large genus Euphorbia shows great
like the English spurges, are annual herbs, others form bushes, while in the desert regions of tropical Africa and the Canary
893 unisexual, the male often containing numerous flowers
flowers
crescent
The form of the flower shows great
4. 5. I. Shoot of Euphorbia hypericifolia, about z nat. size. 2. A partial inflorescence, cyathium, bearing the petaloid glands. 3. A similar one at a later stage, cut open to show the singlestamened (monandrous)male flowers and the central long-stalked female flower. A cyathium without petaloid glandular appendages. A similar one at a later stage with nearly ripe fruit. 6. An anther dehiscing. 7. Fruit dehiscing and exposing one of the three seeds, I. 8. Seed. 9. Seed cut lengthwise exposing the embryo. Io. Diagram of the inflorescence of Euphorbia, illustrating the dichasial' cymose arrangement of the ultimate branches. b, Bract subtending the central terminal cyathium I. a' b', Bracteoles of the first order subtending the secondary cyathia II. a" b", Bracteoles of the second order subtending the tertiary cyathia III. In the central cyathium I. are shown, the details of, the arrangement of the male flowers in monochasial cymes, m, and the central female flower, f. sembling cacti, having thick fleshy stems and leaves reduced to spines. Another large genus, Phyllanthus, contains small annual herbs as well as trees, while in some species the leaves are reduced to scales, and the branches are flattened, forming phylloclades. The leaves also show great variety in form and arrangement, being simple and entire as in the English spurges, or deeply cut as in Ricinus (castor-oil) (fig.. 3), and Manihot or sometimes palmately compound (Hevea). The majority contain a milky juice or latex in their tissues which exudes on cutting or bruising. In Hevea, Manihot and others the latex yields caoutchouc. The flowers are unisexual; male and female flowers are borne on the same, as in the spurges (fig. I), or on different plants, as in dog's mercury (fig. 2). Their arrangement shows considerable variation, but the flowers are generally grouped in crowded definite partial inflorescences, which are themselves arranged in spikes or stand in the axils of the upper leaves. These partial inflorescences are generallyI. Male plant. 5. Fruit beginning to split open. 2. Female plant ; t nat. size. 6. Seed cut lengthwise showing 3. Female flower. the embryo. . Male flower, described in EUPBORI3IA, where the male consists of one stamen separated from its pedicel by a joint , and the female of a naked tricarpellary pistil. The stamens are sometimes more or less united. (monadelphous), and in castor-oil (Ricinus) (fig. 3) are much branched. The ovary generally contains threg chambers, and bears three simple or more often bipartite styles; each chamber contains one or two pendulous ovules, which generallybear a cap-like outgrowth or caruncle, which persists in the seed (well shown in castor oil, fig. 3).As the stamens and pistil are borne by different flowers, cross-fertilization is necessary. In Mercurialis and others with inconspicuous flowers pollination is effected by the wind, but in many cases insects are attracted to the flower by the highly-coloured bracts, as in many Euphorbias and Dalechampia, or by the coloured calyx as in Manihot; the presence of honey is also frequently an attraction, as in the honey-glands on the bracts of the cyathium of Euphorbia. The fruit is generally a capsule which splits into three divisions (cocci), separating from the central column, and splitting lengthwise into two valves. In the mancinil (Ilippomane mancinella) of Central America the fruit is a drupe like a plum, and in some genera berries occur. In the sandbox tree (Hura crepitans) of tropical America the ovary consists of numerous carpels, and forms when mature a capsule which splits with great violence and a loud report into a number of woody cocci. The seeds contain abundant endosperm and a large straight or bent embryo. Several members of the order are of economic importance. From Bentley and Trimen's Medicinal Plants, by permission of J. & A. Churchill. 1. Section of male flower, about 4. Seed. nat. size. 5 and 6. Vertical and transverse 2. Group of stamens sections of seed showing 3. Fruit. embryo in position. Manihot utilissima, manioc or cassava (q.v.), is one of the most important tropical food-plants, its thick tuberous root being rich in starch
arrowroot
The box (Buxus) and a few allied genera which were formerly included in Euphorbiaceae are now generally regarded as forming a distinct orderBuxaceae, differing from Euphorbiaceae in the position of the ovule in the ovary-chamber and in the manner of splitting of the fruit. End of Article: EUPHORBIACEAE If you wish, you can link directly to this article.
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