Seasonal food: watercress

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This could put your nose out of joint - it's our guide to buying, storing, cooking and eating watercress

UK watercress season. Photograph: guardian.co.uk

The health claims made on behalf of watercress are some of the most spectacular of any so-called 'superfood', and as it's been eaten for several millennia there are now plenty of bizarre notions attached to its consumption. Amongst other things it's been suggested as an anti-baldness measure (by the Romans and Anglo-Saxons, the latter are believed to have also applied it externally), in Ireland as a 'pure' food for ascetic hermits, as a mental stimulant aiding decision-making (both the ancient Greek general Xenophon and the Persian king Xerxes made their troops eat it), as a rejuvenator for the more mature lady (Francis Bacon - the Elizabethan one, not the painter) and in common with just about everything edible and by almost everyone, as an aphrodisiac.

Cocking a snook aside, the reliance of today's commercial watercress cultivation on pure, running spring water means a variety of minerals are imparted to the foliage and added to the compounds the plant synthesises itself resulting in an outrageously nutritious vegetable. The plant's preference for slightly alkaline conditions makes the chalk streams of southern England ideal for its cultivation; Arlesford in Hampshire is recognised as the nation's capital of watercress and plays host to an annual festival and one terminus of the Watercress Line, now a heritage steam railway which takes its popular name from its erstwhile function of transporting the local produce to London's markets in double-quick time.

The botanical name for watercress, nasturtium officinale, suggests it's a relative of garden nasturtiums, but despite the latter also having a peppery tang and similarly shaped leaves this is not the case. The word itself comes from the Latin 'nasus tortus', meaning twisted nose, a reference to the wonderful spicy pungency associated with watercress and the mustard with which its branch of the brassica family is most often associated.

Varieties

Watercress thrives rooted in gravel washed over by clear running water, but if you're not fortunate enough to have a spring in your garden it doesn't have to be grown in this manner - somewhere nice and damp will do. If you fancy growing some yourself, buy a nice big bunch from the grocer and plant some sprigs with the roots still attached rather than going out of your way to find it at a garden centre or trying to grow it from seed.

How to buy / what to look for

Freshness is key; crisp, green stems and leaves with no brown patches.

Nutrition

Famously rich in vitamins A and C, magnesium, iron, calcium and folic acid.

Harvested

It's at its best at the spring and autumn ends of a season lasting from April to October in the UK - the heat of midsummer leaves growers striving to prevent the plants from coming into flower and becoming bitter. Some cultivars can be cropped all year round if conditions allow.

Storage

Watercress is best eaten as soon after harvesting as possible. The availability of watercress in the supermarkets is down to the relatively new technique of enclosing it in large, inflated plastic bags which keep the humidity high and protect the stems and leaves from damage. At home, ape these conditions by placing the stems in a glass of water and securing a plastic bag over the top with a rubber band. In the fridge it should be good for a couple of days, but with all the hassle involved it might be easier to either eat it straight away or turn it into soup.

Basic cooking

Most commonly eaten raw. If you're lucky enough to find watercress growing in the wild, treat it with caution - in areas where cows and sheep live it plays host to liver flukes and should only be consumed after either cooking to kill the parasites or the most scrupulous and thorough washing.