The largest family of flowering plants, formerly known as Compositae, and represented in every part of the world except for Antarctica. The flowers are individually small, but are clustered into a head (capitulum) resembling a single flower, with florets seated on receptacles of varied form, and the head surrounded by an involucre, or bracts resembling a calyx. Florets often have no calyx, but sometimes a hairy or scaly pappus develops in the fruit. The corolla is tubular or strap-like and 5-lobed. The 5 stamens are joined into a tube. The ovary is inferior and one-celled, forming an achene. Some have all the florets similar, either all tubular or all strap-shaped; in some (e.g. Bellis, daisy) the outer florets are strap-like and female or neuter, while the inner florets are tubular and usually hermaphrodite. The Asteraceae is closely related to the Dipsacaceae (which, however, has long, usually free stamens, conspicuous calyx teeth, a cup-like epicalyx to each flower, and the ovule pendulous in the ovary, rather than basal). The Asteraceae includes the largest angiosperm genus, Senecio (ragworts and groundsels) with more than 2000 species; and many valuable cultivated plants, e.g. Lactuca sativa (lettuce), Chrysanthemum, Dahlia, and Helianthus annuus (sunflower), as well as many common wild plants. The family comprises 1314 genera with about 21 000 species.
Subjects: Plant Sciences and Forestry.