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Invasive Freshwater Plants and Algae

Water Lettuce

  • Scientific Name

    Pistia stratiotes - Visit ITIS for full scientific classification. 

  • Description


    • Floating colonies with rosettes of ribbed, velvety, light green leaves.
    • Leaves up to 2" wide and 6" long with squared or slightly indented tips.
    • Inconspicuous flower spikes with separate male and female flowers. 
  • Habitat
    • Still or slow-moving, warm, freshwater habitats, often with high nutrient levels.
    • Does not tolerate freezing. 
  • Invasion Pathways and Distribution
    • Introduced from tropical South America.
    • Found worldwide in tropical areas.
    • Can remove heavy metals from water but roots are killed by high levels of pollution.
    • Sold as an ornamental pond or aquarium plant and used for medicine in Asia.
    • It is spread by discarding plants from ponds and aquariums into waterways.
    • In California it is found along the Colorado River and is expected to spread. 
  • Life History
    • Seeds ripen in 4-6 weeks, need light to sprout, and can survive dry or freezing conditions.
    • Also spreads by stolons (a type of stem) that produce new plants.
    • Colonies become large and dense when conditions are right. 
  • Impacts
    • Dense colonies reduce oxygen, light and pH levels in the water, outcompete other aquatic plants, interfere with water flow and recreational activities, increase siltation and provide mosquito habitat. 
  • References and Useful Links

    For references by category and links to other useful AIS sites see our LEARN MORE page.