Cool running water is the growing ground for this member of the mustard family, which can often be found in the wild in and around streams and brooks. Watercress has small, crisp, dark green leaves. Its pungent flavor is slightly bitter and has a peppery snap. Watercress is available year-round and is customarily sold in small bouquets. Choose crisp leaves with deep, vibrant color. There should be no sign of yellowing or wilting. Refrigerate in a plastic bag (or stems-down in a glass of water covered with a plastic bag) for up to five days. Wash and shake dry just before using. Watercress may be used in salads, sandwiches, soups and a variety of cooked dishes. It's also a popular garnish, fast replacing the ubiquitous parsley.