Water lettuce	Status LU: absent.
	Waasserzalot	Status Eur.: established. 1st record: <1850. IAS of EU concern (2022).
	Laitue d’eau	RA: ISEIA: n/a Harmonia+: n/a
	Wassersalat	Wikipedia: | Wikispecies: | CABI
	Watersla	Back to the list of neophytes

Report the species

→ Report Pistia stratiotes to the National Museum of Natural History.

Brief description

Pistia stratiotes L., is often called water cabbage, water lettuce, Nile cabbage, or shellflower. Its native distribution is uncertain but is probably pantropical; it was first discovered from the Nile near Lake Victoria in Africa.It is now present, either naturally or through human introduction, in nearly all tropical and subtropical fresh waterways and is considered an invasive species as well as a mosquito breeding habitat. It floats on the surface of the water, its roots hanging submersed beneath floating leaves.

Water lettuce is among the world’s most productive freshwater aquatic plants and is considered an invasive species. The species can be introduced to new areas by water dispersal, fragmentation, and hitchhiking on marine transportation or fishing equipment. The invasion of Pistia stratiotes in the ecosystem can lead to environmental and socio-economic ramifications to the community it serves. In waters with high nutrient content, particularly those that have been contaminated with human loading of sewage or fertilizers, water lettuce can exhibit weedy overgrowth. It may also become invasive in hydrologically altered systems such as flood control canals and reservoirs. The severe overgrowth of water lettuce can block gas exchange in the surface water, creating hypoxic conditions and eliminating or disrupting various native marine organisms. Blocking access to sunlight, large mats of water lettuce can shade native submerged plants and alter communities relying on these native plants as a source of food. The growth of these mats can also get tangled in boat propellers and create challenges for boaters or recreational fishermen. (Wikipedia contributors 2022).

IAS of Union concern

Pistia stratiotes was first introduced into Europe in the 19th century (Loudon et al. 1850). The first published record of its presence in the wild dates to 1973 in the water canals of the Netherlands (Mennema 1977). An historic overview is given by Živković et al. 2019.

In 2022, Pistia stratiotes L. was added to the list of invasive alien species of Union concern (Anonymous 2022) which implies that member states shall take all necessary steps to prevent its unintentional introduction or spread.

Status and distribution in Luxembourg

Pistia stratiotes L. has not yet been recorded in Luxembourg.

Risk assessment

ISEIA protocol

Not assessed yet.

Harmonia+ protocol

Not assessed yet.

Worldwide distribution

Bibliography

• • Anonymous, 2022. Commission implementing regulation (EU) 2022/1203 of 12 July 2022 amending Implementing Regulation (EU) 2016/1141 to update the list of invasive alien species of Union concern. Official Journal of the European Union L 186: 10 – 13 (13.7.2022).
  • CABI, 2010. Pistia stratiotes. In: Invasive Species Compendium. Wallingford, UK: CAB International. URL: www.cabi.org/isc [accessed 2022-08-19]
  • Loudon JC, Loudon J, Don G, Lindley J, Greville RK, 1850. Loudon’s Hortus Britannicus: A Catalogue of All the Plants Indigenous, Cultivated In, Or Introduced to Britain. Longman, Brown, Green, and Longmans, UK, 735 pp.
  • Mennema J., 1977. Is waterlettuce (Pistia stratiotes L.) becoming a new aquatic weed in the Netherlands. Natura, Netherlands 74: 187–190.
  • Wikipedia contributors, 2022. ‘Pistia stratiotes’, Wikipedia, The Free Encyclopedia, 27 September 2019, 08:25 UTC, <https://en.wikipedia.org/wiki/Pistia> [accessed 2022-08-19]
  • Živković et al., 2019. Pistia stratiotes – a new invasive alien species in Vojvodina (Serbia). BioInvasions Records 8(2): 218–229, https://doi.org/10.3391/bir.2019.8.2.03