Dandelion (Taraxacum officinale)
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The common name Dandelion is given to species of the genus Taraxacum, a large genus of flowering plants in the family Asteraceae. In the Asteraceae (formerly Compositae) the ‘flowers’ are morphologically a composite flower head consisting of many tiny flowers called florets. The dandelion is native to Europe and Asia, and has been introduced to many other places. In northern areas and places where the dandelion is not native, it has become a weedy species, exploiting disturbed ground in human environments. Taraxacum species reproduce asexually by means of apomixis and seed production commonly occurs without pollination.
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 species 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.
Dandelions are used as food plants by the larvae of some species of Lepidoptera. See List of Lepidoptera that feed on dandelions.
Away from their native regions, they have become established in the Americas, Australia and New Zealand as weeds. They are now common plants throughout all temperate regions.