Japanese Knotweed (Fallopia Japonica)
Japanese Knotweed (Fallopia Japonica) is a non-native, alien invasive plant species, originally from Japan & Northern China and it was first introduced to Europe in the 19th Century as an ornamental plant. Today it is rated among the 100 worst invasive species in the world by the Global Invasive Species Programme (GISP).
It is a large herbaceous woody perennial, that has hollow stems with distinct raised nodes that give it the appearance of bamboo, though it is not closely related.
This fast growing perennial can reach 2 to 3 metres in height during the summer. Its hollow, gnarled stems are similar to those of bamboo.
The leaves are heart shaped with a flat bottomed edge arranged on arching stems in a zig zag pattern, and have a lush green colour.
In late summer it produces an abundance of cream white flowers that hang in clusters.
The plant is now widespread across Ireland particularly on roadsides, hedgerows, railways, waste-ground, riverbank and wetland habitats. The invasiveness of the plant is a result of its hardiness and the speed at which it can grow, it quickly forms tall stands shading out the areas below and excluding all other vegetation.
Native plants can rarely compete with this invasive species and local animal plant biodiversity is reduced.
The underground rhizomes are thick and woody with a knotty appearance and when broken can reveal a bright orange-coloured centre, this root system can extend to and beyond a depth of at least 2m and extend 7m laterally from a parent plant.
The underground rhizomes are thick and woody with a knotty appearance and when broken can reveal a bright orange-coloured centre, this root system can extend to and beyond a depth of at least 2m and extend 7m laterally from a parent plant.
During winter, the leaves of the Japanese plant die back to reveal the bamboo type canes that will turn darkish red/brown and die, and the canes can remain standing for several years.
In spring, the plant sends up new shoots, red/purple in colour, with rolled back leaves, and these shoots grow rapidly due to stored nutrients in the extensive rhizome system. Growth rates of up to 40mm a day have been recorded.
Only female Japanese Knotweed plants have been recorded to date in Ireland, therefore it is spread entirely from site to site through the unwitting or accidental movement of rhizome fragments or cut stems.
This plant thrives on disturbance and accordingly invades rural and urban environments where soils are routinely disturbed and transported.
