Water lettuce

Pistia stratiotes


Photo credit: ©Colin Wilson

Water lettuce - Pistia stratiotes

  • Water lettuce is a free-floating plant, with pale-green sessile leaves in rosettes. The leaves are up to 20cm long and 10cm wide, and are covered by white woolly hairs. The flowers are either male or female, with female flowers producing thin-walled, may-seeded fruit. It can also reproduce vegetatively. 

Origin and Worldwide Distribution:
  • It is found across most regions in tropical and subtropical habitats, with major native populations in South and Central America, Africa and south-east Asia. It is also native to the Northern Territory in Australia, with self-controlling regulations.
  • It is found in cooler climates, like Belgium, Czechia, France, Hungary, Italy, the Netherlands, Portugal, Romania, Russia, Slovenia, Spain, Ukraine, and parts of the United States. 

Potential or Known Impacts:
  • It can alter water chemistry by increasing ammonium, nitrate, and phosphorus, and decreasing water pH and dissolved oxygen. Plankton and fish species decline due to the change in water chemistry, increased water siltation, and decreased water velocity. 

How did it/could it get here?
  • It could get here by living in moist soil or through the horticultural/aquarium trade, and associated accidental releases. 

Is it found in Ireland or Northern Ireland?
  • Not found in Ireland or Northern Ireland.

Methods for Prevention:
  • Checking soil, as it can survive for extended periods in moist soil.
  • Avoid dumping unwanted plants, or waste water into rivers, ponds as other waterways.
  • Removing plants from infested waterbodies – may be used as part of a long term maintenance programme.
  • Biological control needs to be carefully tested to ensure that any rust, fungus, or insect species will not impact any native species.
  • Chemical control is advised against, as these chemicals are indiscriminate in what plants are affected.
Invasive Species Ireland

Invasive Species Ireland