Knotweeds

Below are brief description of the types of invasive knotweeds found in Ireland, and the differences betweed them. More detailed information that can be used for identifying can be found here

 

Japanese knotweed (Fallopia japonica)

  • Mature stands grow to approx 1m - 2.5m tall
  • Heart shaped leaf with flat base near the stem. Up to 5 inches long
  • Smooth profile edge on leaf
  • Zig zag structure to the canes/stems
  • Green canes/stems with red/purple speckles. Brown and woody in winter.
  • Bamboo rings at nodes. Stems are hollow.
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    Bohemian knotweed (Fallopia x bohemica)

  • A hybrid between Japonica and Sachalinesis
  • 2- 3m
  • Leaves an intermediate between the two. No flat base and crinkled edge
  • Spreading quicker and could be potentially harder to eradicate
  • Can produce male plants and often produce viable pollen, which could potentially back pollinate with either a Giant or Japanese knotweed plant to produce viable seeds
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    Giant Knotweed(Fallopia sachalinensis)

  • Much taller than Fallopia Japonica 4-5m
  • Leaves 2–3 times bigger. Can be much bigger than an adults hand
  • Have a crinkle around the edge
  • Don't have the distinctive flat base on the leaf

     
     
     

    Himalayan knotweed (Persicaria wallichii)

    • often mistaken for Himalayan balsam as it bears similar colour flowers and also has long lance-like leaves.
    • leaf edge is not as serrated as Himalayan balsam and its stems are bamboo-like, similar to other knotweeds
    • Flowers can range in colour from white to pink and are loosely clustered.
    • Like other knotweeds it can spread vegetatively from cuttings and fragments.
    • Not as common in Ireland as the other knotweed species, although it is considered to be in expansive mode at present.