watercress, hardy perennial European herb ( Nasturtium officinale ) of the family Cruciferae (mustard family), widely naturalized in North America, found in or around water. Often cultivated commercially for the small, pungent leaflets, it is used as a peppery salad green or garnish. Other plants of the genus are sometimes called watercress and are used similarly. Watercress was formerly used as a domestic remedy and against scurvy. The ornamental plant whose common name is nasturtium is unrelated. Watercress is classified in the division Magnoliophyta, class Magnoliopsida, order Capparales, family Cruciferae.