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Himalayan knotweed - Invasive Weed Information

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What Is Himalayan Knotweed - (Persicaria wallichii)?

Habitat: Terrestrial
Distribution in Ireland: Scattered but locally abundant in many places 

Status: Established 

Family name: Polygonacea

Reproduction: Spreads by rhizomes and vegetative propagation

Himalayan Knotweed - (Persicaria wallichii) Flowers and Leaves

Originally introduced as an ornamental garden plant. First recorded in cultivation in 1900 and by 1917 had spread to the wild. Usually found in abandoned gardens and areas where garden waste has been dumped, e.g. roadsides.

Himalayan Knotweed - (Persicaria wallichii) flowers and leaves
Himalayan Knotweed - (Persicaria wallichii) Stem

Himalayan Knotweed Flowers

Himalayan Knotweed Stem

Himalayan Knotweed Leaf

How To Identify Himalayan Knotweed?

Colour: Large lanceolate type leaf often with a reddish mid-rib

Flower: Small white flower

Stem: Bamboo-like stem with red nodes 

Size: Can grow up to 2 metres

Himalayan Knotweed - (Persicaria wallichii) Road-side Stand
Himalayan Knotweed - Persicaria wallichii ID Guide

Himalayan Knotweed - Persicaria wallichii ID Guide

Himalayan Knotweed Stand

Why Is Himalayan Knotweed A Problem?

Can form dense stands that outcompete native species.Die back in the winter can leave areas vulnerable to erosion.

Displaces native species by forming dense stands up to 2m tall and reducing availability of nutrients in the soil. Can reduce the quality of fish and wildlife habitat in riparian areas.

Cutting of the plant without proper site management could cause the plant to spread further.

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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