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Report an Invasive Species

Water lettuce

Water lettuce

Water lettuce

(Pistia stratiotes)

Priority: -  Prevent

Tags: Aquatic | Edible | EDRR

Identification and Reproduction

Identification: 

  • Water lettuce is an aqautic plant that floats above the surface of the water with roots hanging submerged in the water. 
  • This plant does not have a stem, rather leaves are gathered in a rosette. 
  • Rosettes are about 10 cm wide and 6 cm tall. 

  • Leaves are light green, soft, succulent, wavy margins with parallel running veins and can reach up to 14cm in length.
  • Flowers are found in the middle of the rosette. 
  • Roots hang below and appear feathery. 

Reproduction:

  • Water lettuce can reproduce from seeds or vegetatively. 
  • It will produce clones from short, brittle stolons. 
  • Stolons can spread up to 60 cm in length. 

Habitat & Ecology

  • This plant is the most productive freshwater aquatic plant in the world. 
  • Often regarded as a free-floating aquatic plant, water lettuce can still survive in moist soil.
  • It is sensitive to frost and is often restricted to tropical and sub-tropical regions.  
  • It thrives in waters that are high in nutrient content, notably waters that are contaminated with sewage or fertilizers. 

Impacts

Social: 

  • Can block irrigation canals and reservoirs. 
  • Dense mats can clog hydro-electricity turbines and halt energy production.

Ecological: 

  • Dense mats will alter the hydrological properties of ecosystems. 
  • In extreme cases water lettuce can overgrow over the waterbody and block any gas exchange at the air-water interface. This reduces oxygen levels in the water and will kill fish and other organisms. 
  • Large infestations will also out-shade native aquatic species. 
  • Provide a good breeding habitat for mosquitos. Eggs are laid under the leaves and larvae attach to the plant roots. 

Management

Prevention is a high priority for this plant. 

  • Do not plant or purchase this plant to put in your pond or water garden.
  • Never release unwanted plants into natural waterbodies.
  • Learn to identify this plant and avoid traveling infested sites. 
  • Always clean, drain, and dry aquatic equipment like boats or canoes before transferring from one body of water to another.

Mechanical/Manual Control: 

  • Small infestations should be controlled to prevent the subsequent spread. 
  • Harvesters can also be used to remove plants. 
  • Control will be long-term and will need to be repeated. 

Resources

For more details check out the Invasive Species Compendium datasheet on Pistia stratiotes (water lettuce). 

Header photo (Σ64).