The Wit-Sharpening Green of the Stream

Watercress, Nasturtium officinale, is a peppery aquatic plant of clean running water, gathered wild and cultivated in flooded beds since antiquity as one of the oldest of leaf vegetables. The Greeks and Romans esteemed it, and a proverb of the classical world, eat cress, was addressed to the dull-witted in the belief that the sharp green quickened the mind, the pungency of the leaf read as a spur to wit. The Persians were said to feed it to children to make them grow. Its dependence on pure water made it, in plain fact, both a valued food and a rough sign of a clean stream.

In 2014 a nutrient-density study prepared for the United States Centers for Disease Control and Prevention, ranking forty-one fruits and vegetables against seventeen essential nutrients relative to their calories, placed watercress first of all with a perfect score, ahead of better-known greens such as spinach and chard, a modern scientific echo of the ancient regard the Greeks and Persians already paid the plant on nothing more than taste and observation. That old regard was never medical guidance in the way a modern nutrient chart is, but the coincidence between an ancient reputation for vigour and a twenty-first-century laboratory ranking is a rare case of folk instinct and measured nutrition landing on the same plant.