Himalayan knotweed
Koenigia polystachya
Overview
Photo credit: ©GBNNSS; RPS group PLC
Koenigia polystachya
Widely Spread Species:
Habitat:
Origin and Distribution:
Impacts:
How did it get here?:
Is it found in Northern Ireland?
You can help by reporting any sightings: @ the Centre for Environmental Data & Recording (CEDaR) - Or via the iRecord App.
Prevent Spread/Arrival
Current legislative position (Listed on 02 August 2022)
For further queries, you can contact the Invasive Non Native Species (INNS) Team in the Northern Ireland Environment Agency on 028 9056 9558 or Email: invasivespecies@daera-ni.gov.uk
Koenigia polystachya
Widely Spread Species:
- Under Article 19 of Invasive Alien Species Regulation (1143/2014) Himalayan knotweed has been identified as a Widely Spread Species in Northern Ireland and as such, management measures will be put in place to minimise its impacts.
Habitat:
- Himalayan knotweed is a terrestrial plant found across many habitats, including disturbed areas, roadsides, forests, and grasslands
- It may also be found in some freshwater habitats, like riparian zones and irrigation channels
Description:
- Himalayan knotweed is a shrubby perennial plant, measuring 40-120cm in height, and rarely up to 180cm
- Its reddish-brown stem is erect and branching. The stem can range from smooth to densely haired
- The lanceolate to elliptic-lanceolate leaves are smooth to densely hairy on top, and smooth to merely densely hairy or covered with brown woolly soft hairs below
- The flower spike is usually richly branched, wide and measuring up to 11cm long and up to 5.5cm wide
- The flowers are usually creamy white to pinkish and their lobes range between 3-5, with 5 lobes being more common
- The flowers are slightly fragrant, and have styles of different lengths
Origin and Distribution:
- Himalayan knotweed is native to China, Bhutan, Afghanistan, Nepal, Pakistan and Myanmar
- It has been introduced to Austria, Belgium, Czechia, Denmark, France, Germany, Ireland, Italy, Norway, the United Kingdom (Great Britain and Northern Ireland), Canada and New Zealand
Impacts:
- Himalayan knotweed is highly invasive as it spreads vegetatively, grows quickly, shading out native species, and is a habitat generalist
- It can cause declines in native plants, including rare or localised species, due to their quick growth and shading out other plants
- Like other knotweed species, it is difficult and expensive to control
How did it get here?:
- Himalayan knotweed was brought to Great Britain in the early 20th century as an ornamental plant, and has since spread from containment
- It could further be spread by contaminated soils
Is it found in Northern Ireland?
- Present in Northern Ireland
- Distribution information can be found on NBN Atlas Northern Ireland
You can help by reporting any sightings: @ the Centre for Environmental Data & Recording (CEDaR) - Or via the iRecord App.
Prevent Spread/Arrival
- Follow Check Clean Dry protocols to ensure that this plant isn't accidentally introduced or spread further
- Import only clean soil from known sources
- Ensure all vehicles and equipment are cleaned to avoid cross contamination
- Be aware of the threat of colonisation from upstream areas washing Himalayan knotweed material downstream
- Promote native species and biodiversity - use alternative, native plants
- Know what you are buying/growing and source native Irish seed and plants
- Do not swap plants and cuttings
- Never collect plants from the wild
- Safe disposal of plant material and growing media
- Report all sightings
Current legislative position (Listed on 02 August 2022)
- This species must not intentionally be brought into the Union; kept; bred; transported to, from or within the United Kingdom, unless for the transportation to facilities in the context of eradication; placed on the market; used or exchanged; permitted to reproduce, grown or cultivated; or released into the environment.
For further queries, you can contact the Invasive Non Native Species (INNS) Team in the Northern Ireland Environment Agency on 028 9056 9558 or Email: invasivespecies@daera-ni.gov.uk