The family Asteraceae (Compositae) is one of the most successful and largest group of flowering plants on the planet. Their members are most commonly known as weeds of agriculture and gardens, such as daisy (Bellis perennis), creeping thistle (Cirsium arvense) and dandelion (Taraxacum officinale). They are distinguished as having tiny flowers (referred to as florets) that are bunched together into a composite head surrounded by sepal-like bracts. The petals form two types of florets: ray florets which have a tube ending in a petal like strap and disc florets with the tube ending in five short teeth. The flowerheads may have all ray florets (dandelion), all disc florets (thistle) or a combination of both (daisy). the fruit is tiny and often carried on the wind by a pappus, a tiny parachute (Phillips, 1977 Wild Flowers of Britain p. 177).
Dandelion, Taraxacum officinale
Due to lack of fossil evidence, the origin of the Asteraceae is not well understood (Stuessy, 2010 Science 329 pp. 1605-1606). However Barreda et al. (2010, Science 329 p. 1621) describe capitula and pollen grains of Asteraceae from the Eocene of Patagonia in southern Argentina. These fossils are similar in structure to modern day Asteraceae, such as the thistle family, the Carduoideae. Barreda concludes that the ancestral Asteraceae arose in South America.