The family Asteraceae, alternatively Compositae, consists of over 32,000 known species of flowering plants in over 1,900 genera within the order Asterales. Commonly referred to as the aster, daisy, composite, or sunflower family, Compositae were first described in the year 1740. 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. Most species of Asteraceae are annual, biennial, or perennial herbaceous plants, 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. The primary common characteristic is the existence of sometimes hundreds of tiny individual florets which are held together by protective involucres in flower heads, or more technically, capitula. The oldest known fossils are pollen grains from the Late Cretaceous (Campanian to Maastrichtian) of Antarctica, dated to 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 be considered weedy or invasive. Description 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. However, determining genera and species of some groups such as Hieracium is notoriously difficult (see "damned yellow composite" for example). Roots 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. Stems Stems are herbaceous, aerial, branched, and cylindrical with glandular hairs, generally 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 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