Lepidium didymum is an annual or biennial herb with decumbent or ascending and glabrous green stems, up to 40 centimetres (16 in) long, radiating from a central position. The leaves are pinnate and alternate, and can reach a length of 5 cm (2 in). It blooms between July and September. The flowers are inconspicuous, the four white petals very short or absent, with 2 (rarely 4),:54 stamens and the fruits consist of two rounded valves, notched at the apex, with a very short style between.:405 They are also wrinkled and contain orange or reddish brown seeds, that are 1–5 mm long.
Lepidium didymum is of uncertain origin, but is often cited as native to South America, mainly Argentina, Bolivia, Brazil, Chile, Paraguay, Peru, Uruguay and Venezuela. It has been introduced elsewhere as a weed of cultivation. It has naturalised across the globe, from Africa, Europe, Asia, Australasia, North America and South America. In Britain it had been recorded from the wild by 1778, chiefly in England and the south of Ireland, growing on cultivated and waste ground, in gardens and lawns, by paths and roadsides.
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