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Water Lettuce - Invasive Species Information

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Reproduction: The flowers are dioecious, and are hidden in the middle of the plant amongst the leaves. Small green berries form after successful fertilization. The plant can also undergo asexual reproduction. Mother and daughter plants are connected by a short stolon, forming dense mats.

Water Lettuce - Pistia stratiotes free-floating

Water Lettuce free-floating

Water lettuce is among the world's most productive freshwater aquatic plants. In waters with high nutrient content, particularly those that have been contaminated with human loading of sewage or fertilizers, water lettuce can often exhibit weedy overgrowth behavior. It may also commonly become weedy in hydrologically altered systems such as canals and reservoirs

It is a perennial monocotyledon with thick, soft leaves that form a rosette. The plant floats on the surface of the water, its roots hanging submersed beneath floating leaves. The leaves can be up to 14 cm long and have no stem.

How To Identify Water Lettuce?

Leaves: Light green, soft and fleshy with parallel veins, wavy margins and are covered in short hairs which form basket-like structures which trap air bubbles, increasing the plant's buoyancy.

Flowers: Smail creamy-white flowers have fine hairs along margins emerge from rosette centre.

Roots: Feathery roots are suspended beneath the water from floating plant.

Water Lettuce - Pistia stratiotes leaves
Water Lettuce - Pistia stratiotes flower
Water Lettuce - Pistia stratiotes ID Guide

Water Lettuce - Pistia stratiotes ID Guide

Water Lettuce Leaves

Water Lettuce Flower

Why Is Water Lettuce A Problem?

Dense populations of P. stratiotes can clog waterways, making fishing, swimming and boating difficult.  Thick colonies of water-lettuce block the air-water interface which reduces the amount of dissolved oxygen in the water making it less suitable habitat for fish species.  These dense mats can also block animal access to the water and may crowd or shade out native plants upon which other organisms depend for food or shelter. 

What Is Water Lettuce - (Pistia stratiotes)?

Habitat: Aquatic. Fresh water
Distribution in Ireland: Sparse distribution but locally abundant in some places.

Status: Unkown
Family name: Araceae

European Communities (Birds and Natural Habitats) Regulations 2011 non-native invasive plant species A-Z (Updated 2017)

There are currently 35 invasive plant species listed in the European Communities (Birds and Natural Habitats) Regulations (annex 2, Part 1)...


Click on a species from the following list to find out more regarding non-native species subject to restrictions under Regulations 49 and 50.

  1. American Skunk-CabbageLysichiton americanus

  2. Brazilian Giant-RhubarbGunnera manicata

  3. Broad-Leaved RushJuncus planifolius

  4. Cape PondweedAponogeton distachyos

  5. Cord-GrassesSpartina (all species and hybrids)

  6. Curly Waterweed - Lagarosiphon major

  7. Dwarf Eel-GrassZostera japonica

  8. FanwortCabomba caroliniana

  9. Floating PennywortHydrocotyle ranunculoides

  10. Fringed Water-LilyNymphoides peltata

  11. Giant HogweedHeracleum mantegazzianum

  12. Giant KnotweedFallopia sachalinensis

  13. Giant-RhubarbGunnera tinctoria

  14. Giant SalviniaSalvinia molesta

  15. Himalayan BalsamImpatiens glandulifera

  16. Himalayan KnotweedPersicaria wallichii

  17. Hottentot-FigCarpobrotus edulis

  18. Japanese KnotweedFallopia japonica

  19. Large-Flowered WaterweedEgeria densa

  20. Mile-a-Minute WeedPersicaria perfoliata

  21. New Zealand PigmyweedCrassula helmsii

  22. Parrots FeatherMyriophyllum aquaticum

  23. Red AlgaGrateloupia doryphora

  24. RhododendronRhododendron ponticum

  25. SalmonberryRubus spectabilis

  26. Sea-Buckthorn Hippophae rhamnoides

  27. Spanish Bluebell Hyacinthoides hispanica

  28. Three-Cornered LeekAllium triquetrum

  29. WakameUndaria pinnatifida

  30. Water ChestnutTrapa natans

  31. Water FernAzolla filiculoides

  32. Water LettucePistia stratiotes

  33. Water-PrimroseLudwigia (all species)

  34. WaterweedsElodea (all species)

  35. WireweedSargassum muticum

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