Nasturtium officinale

watercress

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Nasturtium officinale R. Br. [= Rorippa nasturtium-aquaticum (L.) Hayek] (Brassicaceae); bronkors (Afrikaans); xi yang cai, dou ban cai (Chinese); cresson de fontaine (French); Brunnenkresse (German); crescione acquatico (Italian); mizu garashi (Japanese); selada air (Malay); agrião (Portuguese); berro (Spanish)

DESCRIPTION Fresh leafy stems are succulent, dark green in colour and have a pungent, peppery taste and distinctive grassy aroma.

THE PLANT An aquatic perennial herb with spreading stems bearing irregularly compound leaves and white flowers. Seeds are borne in oblong capsules and are variously arranged in one or two rows, depending on the species. The generic name for the plant and its close relatives has recently reverted back from Rorippa to Nasturtium.1 Brown watercress, also called winter watercress, is believed to be a hybrid (backcross) between cultivated N. officinale (seeds in two rows) and N. microphyllum (seeds in one row).2 The leaves typically turn purplish brown in winter. The name “cress” is also used for several related culinary herbs, including garden cress (Lepidium sativum) and land cress (Barbarea verna).1

ORIGIN Watercress is indigenous to Europe and has become a cosmopolitan weed of freshwater habitats.1 It has probably been foraged since ancient times but the recorded history as a health food goes back to classical Persia, Greece and Rome. Commercial cultivation only started in the 19th century. Watercress is grown in the United Kingdom in Hertfordshire, Hampshire, Wiltshire and Dorset. Alresford near Winchester, the centre of an annual Wintercress Festival, is considered to be the watercress capital. In the United States, the title of “watercress capital of the world” first went to Huntsville, Alabama but is nowadays associated with Oviedo, Florida.

CULTIVATION On a commercial scale, plants are grown in fresh water (ideally slightly alkaline) in large inundated beds.

HARVESTING The leafy stems are cut by hand, washed (but never left to soak in water) and packed. The picked stems have a limited shelf life of about two days when kept under refrigeration.

CULINARY USES Watercress has become very fashionable in recent years. The leaves are pulled of the stems when eaten raw in salads and sandwiches or used as a garnish. It makes a very tasty soup, often combined with leeks and potatoes. Cooked watercress is prepared in the same way as spinach.3 Watercress purée or watercress dip is made from pounded leaves added to mashed potato or split peas, with variable quantities of the stems included for extra flavour.3 À la cressonnière is the term used in France for dishes that contain watercress.3 In Southeast Asia, it is cooked in soup and not eaten raw.

FLAVOUR COMPOUNDS The pungent, peppery taste is due to the presence of gluconasturtiin, a mustard oil glycoside. By crushing or chewing the leaves, the glycoside is mixed with the enzyme myrosinase, resulting in the formation of two hydrolysis products. These are hydrocinnamonitrile and phenethyl isothiocyanate, the two main flavour compounds.

NOTES Wild-harvested watercress is best avoided as it can transmit parasites.

1. Mabberley, D.J. 2008. Mabberley’s plant-book (3rd ed.). Cambridge University Press, Cambridge.

2. Kiple, K.F., Ornelas, K.C. (Eds). 2000. The Cambridge world history of food. Cambridge University Press, Cambridge.

3. Larousse. 1999. The concise Larousse gastronomique. Hamlyn, London.