Nasturtium officinale / watercress

Adjectives: aquatic, culinary, edible, emergent aquatic, invasive, non-native

Synonym: Rorippa nasturtium-aquaticum
Also known as: yellow cress

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Watercress is a rapidly growing, aquatic or semi-aquatic perennial plant, commonly found in cold, alkaline waters of springs, spring runs, and similar streams. It prefers shallow, slow flowing streams and clean water. Its flowers are white with four petals. Its flowering is triggered by increasing day length, i.e it is a “long-day plant“. The flowers actually show up a bit after that, in mid to late summer. In the US, it has an interesting distribution, being found in all states except North Dakota (at least by one US Forest Service reckoning).

The stems of watercress are hollow and the plant floats. Nevertheless, it is rooted in the muck of the stream bottom. The leaves have a waxy surface that aids in floatation by being hard too wet.

In some regions, watercress is a weed; in others, an aquatic vegetable crop. In South Africa, it is both. In many areas it can be purchased in food markets… it ships well, but as a food, it has very little to offer other than its “piquant” taste: it is 95% water, has only 11 calories per 100 g, and no fat, carbs or protein to speak of. It is, however, a good source of a number of vitamins and minerals so it’s a fine addition to salads.

As for that sharp taste, watercress is one of many members of the brassicaceae noted for this characteristic, other examples being mustard, wasabi, and radish. In all cases, the chemicals responsible for this are part of a mustard oil “bomb” presumed active in defense against herbivores and pathogens.

One caveat, however, if you decide to go watercress collecting… wash it well. Especially in streams in the Valley where animal waste might be present, watercress is a possible source of microparasites, including Giardia.