Dandelion

Dandelions are tap-rooted biennial or perennial herbaceous plants, native to temperate areas of the Northern Hemisphere of the Old World . They are commonly known as weeds or ruderals . The genus is taxonomically very complex, with numerous macrospecies, and polyploidy is also common; over 250 apomictic microspecies have been recorded in the British Isles alone (Richards 1972). Some botanists take a much narrower viewpoint, and only accept a total of about 60 species.

The leaves are 5-25 cm long, simple and basal, entire or lobed, forming a rosette above the central taproot. As the leaves grow outward they push down the surrounding vegetation, such as grass in a lawn, which kills other plants by cutting off their access to sunlight. A bright yellow flower head (which is open in the daytime but closes at night) is borne singly on a hollow stem (scape) which rises 4-30 cm above the leaves and exudes a milky sap ( latex ) when broken. A rosette may produce several flowering stems at a time. The flower head is 2-5 cm in diameter and consists entirely of ray florets . The flower head matures into a spherical "clock" (also known as "wishies") containing many single-seeded fruits ( achenes ). Each achene is attached to a pappus of fine hairs, which enable wind-dispersal over long distances.

Dandelions are used as food plants by the larvae of some species of Lepidoptera ( butterflies and moths ). See List of Lepidoptera that feed on dandelions . Away from their native regions, dandelions have become established in the Americas , Australia and New Zealand and are now common throughout all temperate regions.