Alligator weed

Alternanthera philoxeroides


Photo credit: ©CSIRO
  • Freshwater riverine.

  • The alligator weed is a dense mat-forming aquatic plant; it also may colonise nearby terrestrial habitats. Alligator weed is a tough perennial plant, with hollow stems (growing up to 100cm long), dark green leaves with a visible midrib and arranged in opposite pairs, and paper-like white flowers. In its introduced ranges, it has the ability to reproduce vegetatively though fragments and rhizomes.

Origin and Distribution:
  • Native to the Parana River basin in Brazil

  • Once established the alligator weed rapidly chokes up riverine habitats, reducing both the quality and flow of water and preventing light and oxygen from entering the water column with drastic consequences for the ecosystem and its biodiversity.

Invasion history:
  • It is not clear how this species established itself in Europe as it is not widely traded as an aquarium plant. It might have been introduced by mistake along with other similar ornamental specimens or as a contaminant of these.

Is it found in Northern Ireland?
  • NO, it is currently only established in France and Italy but there is a high risk that it could spread throughout the Mediterranean, as well as in countries with hot  thermal springs.

Prevent Spread/Arrival
    • As the plant is still in an early stage of invasion, placing it now on the Union list will help prevent it from becoming a problem across the EU, by imposing a sales ban, by possibly taking measures on the pathways of unintentional introduction and spread, as well as by taking measures for the rapid eradication of any newly emerging populations and for the management of established populations.
    • Follow Check Clean Dry protocols to ensure that this plant isn't accidentally introduced or spread further.
  • You can help by reporting any sightings @ the Centre for Environmental Data & Recording (CEDaR) - Or via the iRecord App

Current legislative position (Listed on 02 August 2017)
  • This species must not intentionally be brought into the Union; kept; bred; transported to, from or within the United Kingdom, unless for the transportation to facilities in the context of eradication; placed on the market; used or exchanged; permitted to reproduce, grown or cultivated; or released into the environment.
For further queries, you can contact the Invasive Non Native Species (INNS) Team in the Northern Ireland Environment Agency on 028 9056 9558 or Email:  
Invasive Species Northern Ireland

Invasive Species Northern Ireland