THEALES

tea order of dicotyledonous flowering plants, a division of the subclass Dilleniidae. The members are mostly tropical trees and shrubs. Prominent among them are the plants that produce tea and the ornamental camellia. the tea order of flowering plants, belonging to the class called Magnoliopsida (dicotyledon; characterized by two seed leaves). The order comprises 18 families, approximately 175 genera, and 3,400 species. Its members are mostly tropical trees and shrubs. Prominent among them are the plant that produces tea and the camellia. The Theales order is distributed worldwide, with the centre of its range in Southeast Asia. Some species extend into temperate regions, but most are native to rain forests or upland forests of the tropics. The order consists predominantly of evergreen trees or shrubs; some members are woody climbers, and a few are herbs. Tea cultivation is the most important economic activity associated with the group. The tea family, Theaceae, ranges through the tropical and temperate regions of the world. Its members usually have evergreen leaves and showy flowers. The Camellia genus includes the tea plant (C. sinensis), a native of Assam in northeastern India, first cultivated in China. Today tea is grown commercially in India, Sri Lanka, China, Japan, Indonesia, and elsewhere. To produce tea, the leaves of the plant are picked and dried and may be fermented (for black tea), partially fermented (oolong tea), or unfermented (green tea). The ornamental camellia shrub, C. japonica, belongs to the same family and genus as the tea plant and is widely cultivated in temperate areas for its roselike blossoms. The Gordonia and Stewartia genera of this family also include ornamental garden species. The Dipterocarpaceae family consists of resinous trees that grow mainly in the Asian tropics. They form the characteristic high upper canopy of Malaysian rain forests, and many species are economically important for their timber or resins. As the demand for these timbers has increased, the trees have become endangered. The Hypericaceae family includes Saint-John's-wort (Hypericum), cultivated in temperate regions for its handsome flowers. Other families also contain fine horticultural plants, and members of some families produce edible nuts and fruits. The Theales are generally woody plants with simple, often evergreen, leaves. Flowers are radially symmetrical, generally with five sepals and five petals; are usually not brightly coloured; and are bisexual (containing both male and female reproductive structures). Stamens (male) are numerous and may be united in a ring or in bundles, and the ovary (female) consists of several united carpels, or segments. Many members of the order contain resins. In the Dipterocarpaceae family the resins are distributed throughout the plant tissues; in the Hypericaceae and some smaller families, they occur in distinct glands. Remarkable vegetative modifications appear in two families of the order. The Marcgraviaceae, which consists of South American tropical climbers, includes plants (especially in the genus Marcgravia) that give rise to two different types of shoots. The lower ones bear small leaves and produce aerial roots, enabling the shoots to climb; the upper shoots develop larger leaves and flower clusters, and they lack roots. In the Dioncophyllaceae family of west African scrambling shrubs, two or three types of leaves arise on the same plant, one type with hooks that enable the plant to scramble over other vegetation. The Marcgraviaceae also displays a curious floral adaptation associated with pollination. The floral bracts (leaflike structures just below the flowers) are transformed into hollow, nectar-secreting organs. In Marcgravia the bracts enlarge to form erect nectar-filled pitchers that attract hummingbirds. Seeds are dispersed in a variety of ways in the different members of the order, but the Dioncophyllaceae has a method unique among the flowering plants. In this group the fruits open before ripening, and the seeds are pushed out on a stalk, where they mature and drop off, leaving the fruit and stalk on the shrub. Some families adopt another unusual dispersal method, wherein two or more sepals enlarge above the fruit, forming a two-winged structure that is borne away by the wind. Additional reading T. Eden, Tea (1976), an excellent overview of tea, both as plant and product; David L. Feathers and Milton H. Brown, The Camellia (1978), a standard text covering history, culture, and genetics; Bassett Maguire et al., The Botany of the Guyana Highland: Part IX, Tetrameristaceae, Memoirs of the New York Botanical Garden, 23:165192 (1972), a technical account of the discovery and description of a new genus in this small family, capturing the excitement of the dramatic botanical discoveries that result from exploration in the tropics.