Common Name: water lettuce
Type: Herbaceous perennial
Family: Araceae
Native Range: Lake Victoria
Zone: 8 to 10
Height: 0.25 to 0.50 feet
Spread: 0.50 to 1.50 feet
Bloom Time: June to September
Bloom Description: Greenish-yellow to creamy white
Sun: Full sun to part shade
Water: Wet
Maintenance: High
Suggested Use: Annual, Water Plant, Naturalize, Rain Garden
Flower: Insignificant
Leaf: Evergreen
Culture
Easily grown on still water in full sun to part shade. Scatter small bunches of plants on the water surface after last frost date. Plants spread quickly in optimum conditions. Best growth occurs in the cool temperatures of spring and autumn. Remove excess plants as needed. Winter hardy to USDA Zones 8-10. Can be quite invasive in frost-free tropical climates where it is evergreen. In St. Louis, several plants should be lifted each year in fall before first frost for overwintering on moist sandy loams in containers placed in bright frost-free indoor areas of at least 50 degrees F.
Noteworthy Characteristics
Pistia stratiotes, commonly called 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. It is included on the Federal Noxious Weed List. It is also sometimes commonly called shell flower.
Genus name comes from the Greek word pistos meaning water in reference to the floating habit.
Specific epithet comes from Greek meaning soldier in account of the plant's sword-shaped leaves.
Problems
No serious insect or disease problems. Watch for aphids. Can be invasive.
Uses
Free floating aquatic perennial for water gardens or ponds.