Compositae

Compositae The largest family of flowering plants, which represents almost every life-form. The flowers are individually small, but are clustered into heads (capitula, see CAPITULUM) resembling flowers; the florets are seated on receptacles of varied form, and the heads are surrounded by an involucre, or bracts resembling a calyx. The 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 in the fruit. Some have all the florets similar, either all tubular or all strap-shaped; in some the outer florets are strap-like (e.g. Bellis, the daisy) and female or neuter, while the inner florets are tubular and usually hermaphrodite. The family 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, instead of basal, in the ovary). The family includes the largest angiosperm genus, Senecio (ragworts and groundsels), of more than 2000 species; and many valuable cultivated plants, e.g. Lactuca sativa (lettuce), Helianthus tuberosus (Jerusalem artichoke), Tragopogon porrifolius (salsify), as well as oil-producing plants, e.g. Helianthus annuus (sunflower), and many garden plants and serious weeds. The family consists of 1317 genera, with about 21000 species, with a cosmopolitan distribution.