Kingdom: Plantae
Clade: Angiosperms
Clade: Eudicots
Clade: Rosids
Order: Brassicales
Family: Brassicaceae
Genus: Lepidium
Species: L. didymum
Binomial name: Lepidium didymium
Synonym: Coronopus didymus
Common names: Twin cress, Lesser swine-cress, Swine Watercress
Lepidium didymumis a species of flowering plant in the cabbage and mustard family Brassicaceae. Lepidium didymum is of uncertain origin but is often cited as native to South America. It has naturalised across the globe inhabiting mainly human-influenced habitats such as cultivated and waste ground, gardens and lawns, by paths and roadsides.
Lepidium didymum is an annual or short-lived perennial plant that forms a disk-like mat of prostrate shoots radiating from the top of the taproot. It can germinate at any time of the year, though typically it establishes mainly in spring and autumn.
The glabrous, green stems are strongly branched, decumbent or ascending and, up to 40 centimetres long.
The soft, finely divided leaves are hairless, 1-3 cm long and are alternate on the stems. Each leaf is composed of a number of leaflets, and each leaflet has a number of lobes. A distinctive characteristic of Lepidium didymum is that there tend to be more lobes on one side of a leaflet than the other, ie the leaflets are not symmetrical, unlike most other weeds.
Lepidium didymum blooms over summer. The flowers are inconspicuous, the four white petals very short or absent, with 2 (rarely 4), stamens. The fruits that of consist of two rounded, wrinkled valves. They contain orange or reddish brown seeds, that are 1-5 mm long. All parts of the plan have an offensive smell when crushed.
Lepidium didymum can cause major problems on dairy farms if it is eaten by lactating cows, as the milk from these cows will then develop a distinctive taint, It has been suggested that this taint is caused by the inhibitory actions of benzyl isothiocyanate present in the plant on the microbial and/or enzymatic activities in the rumen of the cows.
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