A daisy is not one flower but hundreds packed into a disguise
Pluck a daisy or sunflower and you are holding a crowd. Each head is a capitulum of tiny florets pretending to be a single bloom, with the petals themselves being separate flowers. The trick works so well that the family rivals orchids as the largest group of flowering plants on Earth.
Asteraceae, also known as the daisy, aster, composite or sunflower family, contains over 32,000 known species in more than 1,900 genera. Only the orchids compete for the title of largest plant family, and since nobody knows how many species either holds, the winner is unclear. The family was first described in 1740 under the name Compositae. Most members are herbs, annual, biennial or perennial, though shrubs, vines and trees exist too. They live on every continent except Antarctica, especially in deserts and semi-deserts.
The design is ingenious. A green ring of scale-like bracts, the involucre, protects the developing head, and the florets sit on a dome called the receptacle. The showy rays around the edge are ray florets, strap-shaped flowers of their own, while the central disc is packed with small, radially symmetrical disc florets. Instead of sepals, each floret carries a pappus of bristles or hairs that later helps seeds ride on animal fur or the wind. The name comes from the Greek aster, star, for the rayed look of the heads. Some species even swivel their heads through the day to follow the sun.
The family's roots go deep. The oldest fossils are pollen grains from Antarctica dated to around 76 to 66 million years ago, and the group's crown lineage is estimated to have arisen at least 85.9 million years ago in the Late Cretaceous.
Asteraceae matter economically, supplying food staples, garden ornamentals and herbal remedies, though some become invasive weeds outside their home ranges. They are easy to recognise as a family thanks to their compound heads and joined anthers, yet notoriously hard to sort within some groups. The genus Hieracium is difficult enough to have inspired the phrase damned yellow composite.
Source: Asteraceae
