EUPHORBIALES

order of dicotyledonous flowering plants, a division of the subclass Rosidae. In the strict sense, the order includes only one family, the Euphorbiaceae (spurge). Traditionally, however, a number of other families, especially Buxaceae (boxwood), have been included by various authors, and these are discussed here. diverse order of flowering plants, belonging to the class known as Magnoliopsida (dicotyledons; characterized by two seed leaves). The order contains the very large family Euphorbiaceae, the closely related small family Pandaceae, and two additional small families of more doubtful relationship, Buxaceae (boxwood) and Simmondsiaceae (jojoba). Members of this order yield rubber, edible roots and fruits, medicinal and poisonous compounds, and ornamental plants. They are most abundant in the tropics but are widely distributed throughout the world except in arctic and alpine zones. The unifying features of Euphorbiales are simple leaves (except in a few species), reduced size of flowers, an ovary that rises above the other flower parts (superior position), and few ovules in each ovary chamber. In both habit and habitat, the order is extremely diverse. The spurge family (Euphorbiaceae), one of the larger families of dicotyledons, consists of about 275 genera and about 7,500 species. Its members are distributed worldwide and contribute significantly to the economies of many nations. Cassava, also called yuca, or manioc, is a shrub of South American origin (Manihot esculenta) now cultivated in many tropical lowlands of West Africa and other areas for its edible roots. Tapioca is one of its starchy products. Other members of Euphorbiaceae yield products including commercial waxes (Sapium sebiferum), rubber (Hevea), lumber (Bischofia), tung oil (Aleurites fordii), and castor oil (Ricinus communis). Ornamental plants of the Euphorbiaceae, prized for their colour at flowering time, include the poinsettia (Euphorbia pulcherrima), originally from tropical Mexico and Central America. It is widely sold during the Christmas season in North America. Its showy bracts are foliage leaves that surround clusters of flowers; only the leaves nearest the flowers turn colour. Species of Codiaeum, often known as crotons, are prized for their variegated foliage. Acalypha wilkesiana, or Jacob's-coat, produces bronze-green leaves spotted in colours of copper, red, or purple. The second largest family of the Euphorbiales, the Buxaceae, is largely evergreen and ornamental; its best-known members are the cultivated boxwoods. The family Pandaceae has 4 genera and 18 species of trees, found in tropical areas. One species, Panda oleosa, produces oilseeds. The family Simmondiaceae is entirely composed of Simmondsia chinenses, the fruit of which yields jojoba oil, a substitute for the sperm oil obtained from whales. The diversity of stem habit and structure in the Euphorbiales is extreme. Heights range from cushion plants a few centimetres tall to those measuring 30 m (100 feet). Some are globose, spiny succulents, difficult to distinguish from cacti until flowers appear. Leaf size and shape varies greatly. In most species, a small stipule (bladelike unit) is present basally, on each side of the petiole. Most leaves of the Euphorbiales are evergreen, with some notable exceptions in the spurge family, species of which lack leaves altogether. Weedy perennials, such as the leafy spurge, propagate by rhizomes (underground, horizontal stems) that bear many buds. Although many other special cases of fragmentation occur in some species of Euphorbiales, seeds are overwhelmingly the most important method of reproduction in all families. Flowers in the Euphorbiales may arise singly in the axil of a leaf (upper angle between petiole and stem). In most members, however, several flowers are clustered into various types of inflorescences, from elongate spikes and branched racemes to compact heads. With few exceptions, flowers are either male or female (unisexual); both may be borne on the same plant, depending on the species. In Euphorbia, a cluster of flowers simulates a complete flower. Cross-pollination is the usual method of pollination, though coloured bracts, appendages, and glands of many species also attract a wide variety of pollinating insects. Only a few species are wind-pollinated. After pollination and fertilization, the ovule becomes the seed and the ovary the fruit. Additional reading G.L. Webster, The Genera of Euphorbiaceae in the Southeastern United States, Journal of the Arnold Arboretum, 48(4):303430 (1967), and The Saga of the Spurges: A Review of Classification and Relationships in the Euphorbiales, The Botanical Journal of the Linnean Society, 94:346 (1987); and S.L. Jury et al. (eds.), The Euphorbiales: Chemistry, Taxonomy, and Economic Botany (1987), both general treatments; Alain White, R. Allen Dyer, and Boyd L. Sloane, The Succulent Euphorbisae (Southern Africa), 2 vol. (1941); articles in The Euphorbia Journal (annual).