Affiliation: USDA APHIS Archives Source: Bugwood.org Copyright: CC BY 3.0 US
Water lettuce is very easy to identify: it resembles a floating open head of lettuce and may be found singly or in abundance; its light green leaves are thick, hairy and ridged; its flowers are not seen except by close examination.
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.
Reproduces rapidly by vegetative offshoots formed on short, brittle stolons. Varies seasonally in density of rosettes, from less than 100 to over 1,000 per m2 in south Florida. Seed production, once thought not to occur in North America, now considered important to reproduction and dispersal. Not cold tolerant, but can survive for extended periods of time on moist muck, sandbars, and banks.
Water lettuce has an uncertain origin. There is a large amount of confusion surrounding the origin of water lettuce due to its heavy worldwide distribution. However, it is commonly believed that it is a native of South America or Africa. There is particularly strong evidence linking water lettuce to South America. South America is the location of many regionally native insects associated with water lettuce.
South America to Africa
U.S. Habitat: Water lettuce invades lakes, ponds and slow moving streams in tropical, subtropical and warmer temperate regions.
U.S. Present: AZ, CA, DE, FL, GA, HI, LA, MD, MS, NC, NJ, NY, PR, SC, TX, VI
Resembles/ Alternatives
Native Alternatives: Potamogeton nodosus (longleaf pondweed), Lemna minor (common duckweed)
Contact herbicides such as Endothall and Diquat will act quickly, while systemic herbicides such as Rodeo act slowly. Take care to minimize impacts of herbicide application on native species. Decaying plant material may cause dissolved oxygen depletion.
USE PESTICIDES WISELY: Always read the entire pesticide label carefully, follow all mixing and application instructions and wear all recommended personal protective gear and clothing.
Contributions from Texas Invasives for this species page are greatly appreciated.
Dewald, L. B., & Lounibos, L. P. 1990. Seasonal growth of Pistia stratiotes L. in south Florida. Aquatic botany, 36(3), 263-275.
Dray, F. A., & Center, T. D. 1989. Seed production by Pistia stratiotes L.(water lettuce) in the United States. Aquatic Botany, 33(1), 155-160.
Ferriter, A., Serbesoff-King, K., Bodle, M., Goodyear, C., Doren, B., & Langeland, K. 2004. E: Exotic Species in the Everglades Protection Area. 2004 Everglades Consolidated Report, 11-15.
Holm, L. 1977. Weeds and water in world food production. Weed Science, 338-342.
Internet Sources
http://plants.usda.gov/core/profile?symbol=PIST2
http://plants.ifas.ufl.edu/node/328
http://www.invasive.org/browse/subthumb.cfm?sub=3064
Germplasm Resources Information Network
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