Pistia stratiotes

Water lettuce is a free-floating, frost-tender aquatic perennial that is commonly used as an ornamental plant in water gardens. It produces rosettes (4-6? across) of wedge-shaped, overlapping, fluted, velvety, soft green leaves covered with water-repellant hairs. Plants resemble small open heads of lettuce. New plants are formed at the ends of stolons radiating outward from the mother plant. Plants can spread rapidly to form dense mats of foliage (to 4? tall), and are considered to be noxious weeds in many tropical and sub-tropical areas where they can quickly cover a pond or lake from shore to shore. Tubular, axillary, arum-like, yellowish-green to creamy white flowers are generally inconspicuous. Flowers give way to similarly inconspicuous green berry-like fruits. Feathery roots dangle downward from the plants, providing a shelter for many small fish. As an ornamental plant, water lettuce provides attractive foliage that inhibits growth of algae and helps keep water clear. Although generally believed not to be native to the U.S., water lettuce is now found from New York south to Florida and west to California.