Watercress (Nasturtium nasturtium-aquaticum, N. microphyllum) are fast-growing, aquatic or semi-aquatic, perennials 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 and mustard — all noteworthy for a peppery, tangy flavor.

The stems of watercress are floating and the leaves are pinnately compound. Watercresses produce small, white and green flowers in clusters. Nasturtium officinale Ait. f. and Sisymbrium nasturtium-aquaticum L. are synonyms of N. nasturtium-aquaticum. 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 that the aquatic species with hollow stems are more closely related to Cardamine than Rorippa (Al-Shehbaz & Price, 1998). Watercresses are not related to the flowers in the genus, Tropaeolum (Family Tropaeolaceae), popularly known as "nasturtiums".

Watercress cultivation

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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 exceed supplies. This is due in part to the fact that cress leaves are unsuitable for distribution in dried form and can only be stored for a short period.

However (in the UK at least), the packaging used by supermarkets using sealed plastic bags under some internal pressure (a plastic envelope containing moisture and pressurised (inflated) to prevent crushing of contents) has allowed the distribution of watercress (and sometimes a mixture of it with other salad leaves). This has allowed national availability with a once purchased storage life of 1 - 2 days in chilled / refrigerated storage.

If unharvested, watercress can grow to a height of 50-120 cm. Also sold as sprouts, the edible shoots are harvested days after germination.

Like many plants in this family, the foliage of watercress becomes bitter when the plants begin producing flowers.

Food value

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Watercress contains significant amounts of iron, calcium and folic acid, in addition to vitamins A and C. In some regions watercress is regarded as a weed, in other regions as an aquatic vegetable or herb. Where watercress is grown in the presence of animal waste, it 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 mild stimulant, a source of phytochemicals and antioxidants, a diuretic, an expectorant, and a digestive aid.

References

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• Al-Shehbaz, I. and R. A. Price. 1998. Delimitation of the genus Nasturtium (Brassicaceae). Novon, 8: 124-126.
• ITIS (home page) (visited October 2004)

Herbs | Aquatic plants | Brassicaceae | Leaf vegetables

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