Watercress

Also called  Cress  (Nasturtium officinale), perennial plant, of the mustard family (Brassicaceae), native to Eurasia and naturalized throughout North America in cool, flowing streams where it grows submerged, floating on the water, or spread over mud surfaces. Watercress often is cultivated in tanks for its young shoots, which are used in salads. The plant bears four-petalled, white flowers