Pistia stratiotes L.
Synonym(s): tropical duckweed

Water lettuce is a free floating herbaceous plant that invades aquatic environments in the warmer regions of the United States. The leaves occur in a rosette and are gray-green, spongy, 0.8-6 in. (2-15 cm) long with deep, parallel veins. Flowering occurs in late summer to early winter, but plants have been observed flowering nearly all year. The inconspicuous flowers are clustered near the stalk. The fruit is a many-seeded, green berry. Water lettuce invades lakes, ponds and slow moving streams in tropical, subtropical and warmer temperate regions. High vegetative reproduction allows water lettuce to form dense floating mats of vegetation. Severe infestations block light to the water ecosystem, reduce oxygen levels, increase siltation, reduce suitable fish spawning habitat and restrict water flow and boating traffic. Water lettuce is believed to be native to Africa or South America, but it is widely distributed throughout the world’s tropical areas. The plant was identified in North America as early as the late 1700s.

Identification, Biology, Control and Management Resources