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Floating Pennywort - Invasive Species Information

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What Is Floating Pennywort - (Hydrocotyle ranunculoides)?

Habitat: Aquatic, waterways, ponds and ponds
Distribution in Ireland: Sparse distribution but locally abundant in some places.

Status: Established
Family name: Apiaceae.

Reproduction: Vegetative growth can be very rapid, with floating mats extending up to 20 cm per day its growth rate is highest in the summer months June and July.

Floating Pennywort - Hydrocotyle ranunculoides leaf

Floating Pennywort - Hydrocotyle ranunculoides Leaf

Floating pennywort Native to North and South America and parts of Africa and is an aquatic plant in the family Apiaceae.  In Ireland it is an invasive alien species which is currently spreading in waterways. Floating pennywort has stems that spread horizontally and can float on water. 


Leaves grow on petioles up to 35 cm long, and are round to kidney-shaped, with 3–7 lobes and crenate to entire margins.

How To Identify Floating Pennywort?

Colour: Flowers are small, pale greenish white to pale yellow, and come in umbels of 5–13. Fruits are small achenes that can float, helping the seeds to disperse

Floatin Pennyort Infestation
Floating Pennywort Flower
Floating Pennywort - Hydrocotyle ranunculoides ID Guide

Floating Pennywort - Hydrocotyle ranunculoides ID Guide

Floating Pennywort Flower

Floating Pennywort Root

Why Is Floating Pennywort A Problem?

competes with many native plant species. which are overgrown and shaded out by the extensive beds or floating carpets. Species richness of native aquatic plants may be reduced and submerged species may even disappear entirely. Floating pennywort can cause major problems in nature reserves, recreation areas and intensely managed waterways.


The floating mats not only affect the penetration of light available for photosynthesis, but also reduce oxygen levels in the water column which can result in fish mortality and influence invertebrate life, leading to sediment anoxia, the release of nutrients and potentially toxic substances can be enhanced.


Rapid biomass accumulation fuels decomposition processes, alters the composition of the bottom substrate and expedites the infilling of shallow standing waters. In flowing waters, drainage is impeded and siltation increases with heavy infestation. 

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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