Asteraceae

Asteraceae (/ˌæstəˈreɪsi.iː, -ˌaɪ/ ^ⓘ) is a large family of flowering plants that consists of over 32,000 known species in over 1,900 genera within the order Asterales. The number of species in Asteraceae is rivaled only by the Orchidaceae, and which is the larger family is unclear as the quantity of extant species in each family is unknown. The Asteraceae were first described in the year 1740 and given the original name Compositae. The family is commonly known as the aster, daisy, composite, or sunflower family.

Most species of Asteraceae are herbaceous plants, and may be annual, biennial, or perennial, but there are also shrubs, vines, and trees. The family has a widespread distribution, from subpolar to tropical regions, in a wide variety of habitats. Most occur in hot desert and cold or hot semi-desert climates, and they are found on every continent but Antarctica. Their common primary characteristic is compound flower heads, technically known as capitula, consisting of sometimes hundreds of tiny individual florets enclosed by a whorl of protective involucral bracts.

The oldest known fossils are pollen grains from the Late Cretaceous (Campanian to Maastrichtian) of Antarctica, dated to c. 76–66 million years ago (mya). It is estimated that the crown group of Asteraceae evolved at least 85.9 mya (Late Cretaceous, Santonian) with a stem node age of 88–89 mya (Late Cretaceous, Coniacian).

Asteraceae is an economically important family, providing food staples, garden plants, and herbal medicines. Species outside of their native ranges can become weedy or invasive.

Members of the Asteraceae are mostly herbaceous plants, but some shrubs, vines, and trees (such as Lachanodes arborea) do exist. Asteraceae species are generally easy to distinguish from other plants because of their unique inflorescence and other shared characteristics, such as the joined anthers of the stamens. Nonetheless, determining genera and species of some groups, such as Hieracium, is notoriously difficult (see "damned yellow composite" for example).

Members of the family Asteraceae generally produce taproots, but sometimes they possess fibrous root systems. Some species have underground stems in the form of caudices or rhizomes. These can be fleshy or woody, depending on the species.

The stems are herbaceous, aerial, branched, and cylindrical with glandular hairs, usually erect, but can be prostrate to ascending. The stems can contain secretory canals with resin, or latex, which is particularly common among the Cichorioideae.

Leaves can be alternate, opposite, or whorled. They may be simple, but are often deeply lobed or otherwise incised, often conduplicate or revolute. The margins also can be entire or toothed. Resin or latex can also be present in the leaves.