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New Zealand Pigmyweed - Invasive Species Information

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Reproduction: Tiny fragments of the stem can regrow and multiply into a dense mat of vegetation.

Newzealand Pigmyweed - (Crassula Helmsii) - Coommon Name: Australian Swamp Stonecrop Flower

Zealand Pigmyweed Flower

Originally found in Australia and New Zealand, it has been introduced around the world. New Zealand pygmyweed grows in ponds, lakes, reservoirs, canals and ditches as well as on damp mud on the margins of ponds and reservoirs. It tolerates a wide range of conditions, from basic to acidic and oligotrophic to eutrophic. 


This perennial plant forms carpets with 100% cover, or semi-submerged in deeper water, or totally submerged with elongated stems. It does not die back in winter.


New Zealand pygmyweed is also known as Tillaea aquatica, Australian Swamp-stonecrop, and Briweg.

How To Identify New Zealand Pigmyweed?

Stem: Pink, rigid and round


Leaves: Narrow and pointed up to 2cm long and in opposite linear pairs. Leaf bases joined around the stem to form a collar. Leaves are fleshy when emergent and flatter when permanently submerged


Flower: Very small star-like, with 4 whitish petals. Blooms between June and September. flowers are often absent 

New Zealand Pigmyweed - Crassula helmsii ID Guide V4.gif

New Zealand Pigmyweed - Crassula helmsii ID Guide

New Zealand Pigmyweed - Crassula helmsii leaves
New Zealand Pigmyweed - Crassula helmsii flowers
New Zealand Pigmyweed - Crassula helmsii leaves

New Zealand Pigmyweed Leaves and Flowers

Why Is New Zealand Pigmyweed A Problem?

Forms thick dense mats which can float or be submerged. The thick mats cause shading of existing water plants and the depletion of oxygen in the water, which leads to a reduction of native ora and fauna.


Possible health hazard, as the thick mats can be mistaken for dry land.

The species can move onto a terrestrial habitat after it colonises an aquatic area. Can obstruct boats and reduce the opportunities where fishing can take place, which may impact upon local economies.

What Is New Zealand Pigmyweed - (Crassula helmsii)?

Habitat: Aquatic, Freshwater
Distribution in Ireland: localised distribution in the wild but with many occurrences in arti cial waterbodies
Status: Established
Family name: Crassulaceae

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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