Bohemian knotweed
Reynoutria × bohemica
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Photo credit: RPS group Plc
Reynoutria × bohemica – Bohemian knotweed
Description:
Habitat:
Origin and Distribution:
Impacts:
Is it found in Northern Ireland?
How did it get here?
Prevent Spread
You can help by reporting any sightings:@ the Centre for Environmental Data & Recording (CEDaR) - Or via the iRecord App.
Current legislative position (Listed on 07 August 2025)
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
Reynoutria × bohemica – Bohemian knotweed
Description:
- A hybrid which is the product of spontaneous crosses between Japanese knotweed and giant knotweed.
- An erect, arching semi-woody perennial plant which forms dense thickets 2.5 – 4m tall.
- Each stem bears stalked, broadly ovate leaves up to 23 cm long with a pointed tip and moderately rounded base.
- Bears small greenish-white flowers in dense panicles.
- Primary means of dispersal is vegetative. It grows readily and vigorously from pieces of rhizome and green stem.
Habitat:
- It is a lowland plant, forming dense thickets on waste ground, roadsides, railway embankments and cuttings and on river and canal banks.
Origin and Distribution:
- This hybrid was first described in the Czech Republic in 1983 and is now found globally.
Impacts:
- Forms dense, tall thickets that outcompete native vegetation for space, light, nutrients, and water.
- Large colonies alter ecosystem structure and species composition, affecting plants and animals, especially in riparian areas.
- Dense growth on riverbanks can restrict access.
- Winter dieback on riverbanks can expose soil to flood erosion, requiring costly removal and reinforcement.
- High eradication costs can sometimes deter development and may reduce land values.
Is it found in Northern Ireland?
- Yes, but it may be under recorded due to misidentification/confusion with Japanese knotweed or giant knotweed.
How did it get here?
- It is not clear when or how the hybrid arose, but the parent species have been present in Northern Ireland for many years, originally introduced as ornamental plants.
Prevent Spread
- Follow Check Clean Dry and Be Plant Wise protocols to ensure that this plant isn't accidentally introduced or spread further.
- Don’t strim, cut, flail or chip knotweed plant parts as tiny fragments can regenerate new growth.
- Report all sightings.
You can help by reporting any sightings:@ the Centre for Environmental Data & Recording (CEDaR) - Or via the iRecord App.
Current legislative position (Listed on 07 August 2025)
- In August 2025 bohemian knotweed was listed by the EU as a Species of Union Concern meaning landowners have a legal obligation to prevent this species spreading from their land ‘into the environment’.
- 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