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(also Asteraceae), a family of dicotyledonous plants comprising approximately 25,000 species (according to other data, 13,000–20,000), belonging to 900–1,000 genera. The plants are found throughout the world, in every climatic zone. Most are herbaceous plants. Subshrubs and undershrubs are often present in temperate latitudes, and shrubs and trees are found in the tropics. Lianas, aquatic species, and swamp species are rare.
Composite plants usually have alternate leaves, although species having opposite or whorled leaves are sometimes encountered. The leaves are most often exstipulate. The flowers are gathered in a capitate inflorescence, which is known as a head. The broad, common flower receptacle is most commonly cup-shaped, saucer-shaped, or spherical; conical receptacles and receptacles of other shapes are less common. The receptacle usually hold numerous small flowers. The head is surrounded by an involucre of scalelike or grassy leaf bracts, which usually have appendages. Sometimes the involucre is formed only of slightly modified apical leaves. The common flower receptacle often bears the flowers in the axils of altered and reduced bracts. Often the heads are gathered into a larger inflorescence, which may be racemose, cymose, or some other form. The corolla is gamopetalous and composed of five parts. In regular flowers it is usually funnel-shaped or in the form of a narrow tube; in irregular flowers it is generally ligulate or, less frequently, bilabiate. All the flowers in a head may be the same type—all tubular, all ligulate, or all bilabiate. Frequently the flowers in the center of the head are different from those at the edge.
There is no calyx, and in its place many composite species have a pappus in the form of a pellicular border or a pappus of bristles or pellicles. The pappus, which plays a role in fruit dispersal, is usually considered to be a calyx that has been altered in the process of evolution. There are five stamens, which are attached to the tube of the corolla. The filaments are most often free, whereas the anthers are usually attached to each other, forming the tube. The gynoecium is formed by two carpels, and the inferior ovary is one-celled. The style extends through the tube of the anthers and ends in two stigmal rami, below which there is often a crown of little hairs that serve to clear away the pollen. The fruit is an achene.
In the flora of the USSR, as in the flora of many countries of the northern hemisphere, the Compositae have more representatives than any other family. The USSR has more than 3,500 species, belonging to approximately 225 genera. Composite plants are the most highly organized dicotylendonous plants; they are the best adapted plants for pollination, fertilization, and fruit dispersal. Contemporary classifications consider the most primitive tribe to be the Heliantheae and the most perfect tribe to be the Lactuceae (Cichorieae). The Compositae are represented by two subfamilies: Asteroideae (Carduoideae, or Tubuliflorae) and Lactucoideae (Cichoroideae, or Liguiflorae). The former subfamily contains 11 tribes, and the latter has only one tribe.
The family Compositae includes many economically important plants. Oil plants include sunflower, tarweed, and safflower. Important vegetable plants are lettuce, artichoke, chicory, and endive. The Jerusalem artichoke is a valuable feed crop. Medicinal plants include lavender cotton, wild chamomile, arnica, and inula. Guayule is among the important rubber plants. There are numerous ornamental plants, for example, dahlias, asters, chrysanthemums, pot marigolds, and marigolds. A number of composite plants are pernicious weeds, including ragweed, sow thistle, centaury, thistle, and cocklebur.
REFERENCESTakhtadzhian, A. L. Sistema ifilogeniia tsvelkovykh rastenii. Moscow-Leningrad, 1966.
Flora SSSR, vols. 25–30. Moscow-Leningrad, 1959–64.
Poliakov, P. P. Sistematika i proiskhozhdenie slozhnotsvetnykh. Alma-Ata, 1967.
Cronquist, A. “Phylogeny and Taxonomy of the Compositae.” American Midland Naturalist, 1955, vol. 53, no. 2.
Solbrig, O. T. “Subfamilial Nomenclature of Compositae.” Taxon, 1963, vol. 12, no. 6.
M. E. KIRPICHNIKOV