Japanese Knotweed
Reynoutria japonica
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Almost every plant in Britain is female, and genetically one single clone.
A vigorous perennial with hollow, bamboo-like reddish-speckled stems, broad shield-shaped leaves in a distinctive zig-zag arrangement, and sprays of creamy-white flowers in late summer. Introduced as an ornamental in the nineteenth century, it grows on riverbanks, waste ground, railway land and roadsides around Dumfries.
Behaviour
Every British plant is thought to descend from a single female introduction, making the national population effectively one clone — so it sets no viable seed here and spreads entirely from fragments of rhizome, which can regenerate from a piece the size of a fingernail. The rhizomes reach several metres and can exploit weaknesses in tarmac and foundations. Moving contaminated soil is an offence.
When to see it
Quick facts
- Family
- Docks and knotweeds (Polygonaceae)
- Height
- Up to 3 m
- Status
- Invasive non-native; offences apply to spreading it or its soil
CC0, via Wikimedia Commons