Cross section of a sunflower, a member of the aster family

aster [Gr.,=star], common name for the Asteraceae (Compositae), the aster family, in North America, name for plants of the genus Aster, sometimes called wild asters, and for a related plant more correctly called China aster (Callistephus chinensis), all members of the family Asteraceae (aster or composite family). Asterceae is one of the largest families of vascular plants, totaling an estimated 1,150 genera and perhaps 25,000 species. They are distributed over most of the earth and in almost all habitats and climates. North American genera number about 230, of which 20 are believed to be naturalized from Europe. The greatest number of composites are herbaceous. In the typical composite flower (e.g., the sunflower), what appears to be a single flower is actually a head of many small flowers. Petallike flowers of the outer ring are called ray flowers, and are often only pistillate. The central portion of the head is composed of disk flowers, minute tubular florets nearly always containing both stamens and pistils. The entire composite head is supported by a series of bracts (modified leaves), which arise from the base of the flower stalk and are collectively termed the involucre. The fruits of asters are known as achenes. The family includes many common weeds and wildflowers. A few species are used for food, usually as salad plants—e.g., lettuce, endive and chicory; the artichoke and lettuce are the only commercial table vegetables and safflower is a source of oil. Many composites have been used in medicinal preparations. The family is most valuable for its well-known and numerous cultivated ornamentals such as asters, daisies, chrysanthemums, marigolds, and zinnias. In North America, where most species are native, plants of the genus Aster are regarded as wildflowers, but in Europe they are cultivated as garden flowers and often called Michaelmas daisy (they usually bloom at Michaelmas). Most species of Aster are perennial and fall-blooming. They have small, daisylike or starlike flower heads on leafy, often tall, stems. Their colors vary from white to pink, blue, and purple. Among the more showy native species cultivated in North American gardens are the purple New England aster (A. novae-angliae) and the violet or blue New York aster (A. novi-belgii). The China aster is the common aster of florists and flower gardens. It is an Asian plant that in cultivation has a very full head of ray flowers, varying from white and pink to deep purple. Other related genera with similar flowers are sometimes called asters, e.g., the golden asters (Chrysopsis). Asters are classified in the division Magnoliophyta, class Magnoliopsida, order Asterales.

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