A plant that is a member of the mustard family and is used as an herb and a salad green. It originated in eastern Europe and western Asia and now grows throughout the world. It grows mainly in clear ponds, springs, and slow running creeks. In the United States, it is cultivated in the mid-Atlantic and southern states using special growing beds. It has a very long root system and clusters of dark green leaves that grow above the water. The leaves have a savory, spicy flavor making them very suitable for salads, sandwiches, or for adding flavor to many dishes. It is only harvested from clean water and is washed thoroughly after harvesting to remove any insect larvae that may be present.