Watercress is a member of the mustard family. Watercress grows in stream beds, forming masses of pungent, dark green sprigs. Its pungent flavor is slightly bitter and has a peppery taste. Selection: Choose crisp leaves with deep, vibrant color. Avoid watercress with yellow or slimy leaves. Storage: Refrigerate in a plastic bag (or stems-down in a glass of water covered with a plastic bag) for up to 5 days.