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, many-seeded fruit. It can also reproduce vegetatively. 
  • Download N.I.E.A. ID guide

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 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:
  • Report sightings.
  • Prevent spread by ensuring that equipment (e.g. kayaks, fishing poles, Wellington boots) are free from fragments to prevent spread elsewhere. See Check Clean Dry for further information.
  • 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.
  • Chemical control is advised against, as these chemicals are indiscriminate in what plants are affected.

You can help by reporting any sightings:
Current Legislation Position:
  • Pistia stratiotes is listed in Schedule 9 of the Wildlife (Northern Ireland) Order 1985 and as such, under Article 15 it is an offence to plant or otherwise cause this species to grow in the wild.

Species Related Files:

Invasive Species Ireland

Invasive Species Ireland