Watercress is a small leafy green plant that grows in shallow running water — streams, springs, and beds specially flooded for it. The leaves are round and dark green, the stems are hollow and crisp, and the taste is peppery and slightly bitter, a bit like a mild radish or rocket. It bites back a little, which is exactly why people like it.

In British cooking it is very traditional: watercress soup, watercress sandwiches, watercress under a piece of roast meat or beside smoked salmon. It has a slightly old-fashioned, countryside feeling in Britain. In Taiwan and southern China the same plant is thoroughly familiar but treated quite differently — it goes into soup, often long-simmered with pork bones, or is stir-fried with garlic, and nobody thinks of it as an English salad at all. So this is one of those words where the English name and the Chinese name point to the same plant but bring completely different meals to mind.

It is an uncountable noun: you buy 'some watercress' or 'a bunch of watercress', never 'a watercress' or 'two watercresses'. Because it grows in water that may come from farmland, wild watercress needs washing carefully — this is a plant people are told to buy rather than pick.