Watercresses (Nasturtium officinale, N. microphyllum; formerly Rorippa nasturtium-aquaticum, R. microphylla) are fast-growing, aquatic or semi-aquatic, perennial plants native from Europe to central Asia, and one of the oldest known leaf vegetables consumed by human beings. These plants are members of the Family Brassicaceae or cabbage family, botanically related to garden cress, mustard and radish — all noteworthy for a peppery, tangy flavour.
The hollow stems of watercress are floating, and the leaves are pinnately compound. Watercresses produce small, white and green flowers in clusters.
Nasturtium nasturtium-aquaticum (nomenclaturally invalid) and Sisymbrium nasturtium-aquaticum L. are synonyms of N. officinale. Nasturtium officinale var microphyllum (Boenn. ex Reich.) Thellung is a synonym of N. microphyllum (ITIS, 2004). These species are also listed in some sources as belonging to the genus Rorippa, although molecular evidence shows the aquatic species with hollow stems are more closely related to Cardamine than Rorippa. Watercresses are not closely related to the flowers in the genus Tropaeolum (Family Tropaeolaceae), popularly known as "nasturtiums".
Cultivation of watercress is practical on both a large scale and a garden scale. Being semi-aquatic, watercress is well-suited to hydroponic cultivation, thriving best in water that is slightly alkaline. It is frequently produced around the headwaters of chalk streams. In many local markets, the demand for hydroponically grown watercress exceeds supply, partly because cress leaves are unsuitable for distribution in dried form, and can only be stored fresh for a short period.
Watercress can be sold in supermarkets inside sealed plastic bags, containing a little moisture and lightly pressurised to prevent crushing of contents. This has allowed national availability with a once-purchased storage life of one to two days in chilled/refrigerated storage.
Also sold as sprouts, the edible shoots are harvested days after germination. If unharvested, watercress can grow to a height of 50 120 cm. Like many plants in this family, the foliage of watercress becomes bitter when the plants begin producing flowers.
In the United States in the 1940s, New Market, Alabama was known as the "Watercress Capital of the World".
Watercress is grown in a number of counties of the United Kingdom, most notably Hertfordshire, Hampshire, Wiltshire and Dorset, although the first commercial cultivation was along the River Ebbsfleet in Kent grown by William Bradbery (horticulturist) in 1808. Alresford, near Winchester, is often considered the watercress capital of Britain (to the extent that a steam railway line is named after the famous local crop). In recent years, watercress has become more widely available in the UK, at least in the South-East, being stocked pre-packed in some supermarkets, as well as fresh by the bunch at farmers' markets and greengrocers. Value-added products, such as the traditional watercress soup and pesto, are increasingly easy to source.
Watercress contains significant amounts of iron, calcium and folic acid, in addition to vitamins A and C. Because it is relatively rich in Vitamin C, watercress was suggested (among other plants) by English military surgeon John Woodall (1570 1643) as a remedy for scurvy. In some regions, watercress is regarded as a weed, in other regions as an aquatic vegetable or herb. Watercress crops grown in the presence of manure can be a haven for parasites such as the liver fluke Fasciola hepatica.
Many benefits from eating watercress are claimed, such as that it acts as a stimulant, a source of phytochemicals and antioxidants, a diuretic, an expectorant, and a digestive aid. It also appears to have antiangiogenic cancer-suppressing properties; it is widely believed to help defend against lung cancer. A 2010 study conducted by the University of Southampton found that consumption of watercress may also inhibit the growth of breast cancer. The content of phenethyl isothiocyanate (PEITC) in watercress inhibits HIF, which can inhibit angiogenesis.
Due to its high iodine content, watercress has a strengthening effect on the thyroid gland, thus it is beneficial for sufferers of hypothyroidism.
Watercress is mentioned in the Talmud as being able to stop bleeding, when mixed with vinegar.
Watercress is a known inhibitor of the cytochrome P450 CYP2E1, which may result in altered drug metabolism for individuals on certain medications such as chlorzoxazone.
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