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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 fruitsfruit,
matured ovary of the pistil of a flower, containing the seed. After the egg nucleus, or ovum, has been fertilized (see fertilization) and the embryo plantlet begins to form, the surrounding ovule (see pistil) develops into a seed and the ovary wall (pericarp) around the
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 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 MagnoliophytaMagnoliophyta
, division of the plant kingdom consisting of those organisms commonly called the flowering plants, or angiosperms. The angiosperms have leaves, stems, and roots, and vascular, or conducting, tissue (xylem and phloem).
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, class Magnoliopsida, order Asterales.

Aster

 

the name of two genera of plants, Aster and Callistephus, of the aster family (Compositae). The only species of the Callistephus genus is the so-called China or annual aster (C. chinensis), an annual with large individual anthodia of blossoms. It grows wild in China and Japan and is the ancestor of the decorative annual double and single asters.

About 4,000 varieties of cultivated asters are known, differing in the form of their blossom clusters, the hues of the ligulate and tubular florets of their flowers, and the height and branching of the whole plant. Annual asters are divided into more than 40 groups according to the form of their flowers and blossom clusters. The most common are the pompon, rose-flowered, peony-flowered, Comet, Ostrich Plume, Victoria, American Beauty, and California varieties. The plants vary in height from low (15–25 cm), used for borders, and medium (30–50 cm) to high (60–80 cm), useful for planting on lawns and for cutting. Cut plants last in water for ten to 20 days. In the temperate zone of the USSR annual asters are grown outdoors by transplanting seedlings or sowing seeds in open ground.

Plants of the genus Aster are perennial grasses with alternate leaves. The flowers occur in anthodia gathered into racemes or corymbs, or more rarely occurring singly. About 200 species are known, found mainly in North America but also in South America, Africa, Asia, and Europe. In the USSR there are about 30 species, found from the tundra to the steppe zone in meadows, steppes, and sunny, leafy forests, as well as in the mountains in Alpine meadows. Many writers divide the genus Aster into a number of independent genera. Cultivated plants include the Alpine aster (A. alpinus), grown in the Altai and the Caucasus, and the European aster (A. amellus), grown in the central southern zones of the European USSR, the Caucasus, and Western Siberia. The majority of garden varieties of perennial aster have branching, upright bushes from 20 to 150 cm high (depending on species and variety). The flower anthodia of most varieties are single, and their ligulate blossoms are lilac-colored, white, pink, red, or bluish; the tubular blossoms are usually yellow, and more rarely (in the double varieties) the same colors as the marginal ones. There are early-blooming asters (from late May to early June), midsummer asters (July to August), and late-blooming asters (late August to late October). Perennial asters are highly resistant to cold, tolerating temperatures of 4–7° C. Asters are planted in both homogeneous and mixed beds. The short varieties are used in borders, and the tall varieties are planted around decorative shrubbery or used for cutting. They are propagated by the dividing of bushes, as well as from sprouts, grafts, and seeds.

REFERENCE

Stroganova, T. P. Astry, 2nd ed. Moscow, 1960.

N. A. BAZILEVSKAIA

aster

[′as·tər]
(botany)
Any of the herbaceous ornamental plants of the genus Aster belonging to the family Compositae.
(cell and molecular biology)
The star-shaped structure that encloses the centrosome at the end of the spindle during mitosis.

aster

1. any plant of the genus Aster, having white, blue, purple, or pink daisy-like flowers: family Asteraceae (composites)
2. China aster a related Chinese plant, Callistephus chinensis, widely cultivated for its showy brightly coloured flowers
3. Cytology a group of radiating microtubules that surrounds the centrosome before and during mitosis