Invasive Freshwater Plants and Algae

Water Lettuce

• Scientific Name

  Pistia stratiotes - Visit ITIS for full scientific classification. 

• Description

  

  Water Lettuce (The small plants between the Water Lettuce are Giant Salvinia). Joseph DiTomaso. © 2005 Regents, University of California

   

  • 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.