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Reproduction: Typically displays little variation in growth patterns throughout the year when grown in tropical environ-ments; however, when grown in more moderate environments the plant spends most of its energy on starch production and storage in the winter and canopy growth during the summer season. Can spread through transport of plant fragments.

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Submerged Large-flowered Waterweed

Submerged Large-flowered Waterweed

Large-flowered Waterweed is an Aquatic plant native to Argentina, Brazil, and Uruguay, growing in water up to 4 m deep, with trailing stems to 2 m or more long, producing roots at intervals along the stem.


Leaves are produced in whorls of four to eight, 1–4 cm long and 2–5 mm broad, with a pointed leaf tip.


The stem system of the plant will grow until it reaches the surface of the water, where it will begin to spread out, creating a thick flower canopy that blocks light from reaching plants below it.

How To Identify Large-flowered Waterweed?

Leaf: Whorled green leaf 4-8 1-4 cm long with pointed tip

Flower: white with 3 petals and yellow stamen

Roots: Appear along stems, can grow up to 4m deep

Large-flowered Waterweed - Egeria densa Flowers
Large-flowered Waterweed - Egeria densa Flowers

Large-flowered Waterweed - Egeria densa Flowers

Large-Flowered Waterweed Egeria densa ID Guide

Large-flowered Waterweed - Egeria densa ID Guide

Why Is Large-flowered Waterweed A Problem?

Out competes native species. Most of its impact occurs in the shallow waterways; the plant forms thick mats that obstruct boat passage, clog water intakes and aqueducts, trap sediments, crowd out native vegetation, and impede the migration of anadromous fish.

Large-flowered Waterweed - Invasive Species Information

What Is Large-flowered Waterweed - (Egeria densa)?

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

Status: Established
Family name: Hydrocharitaceae

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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