Identifying Japanese Knotweed

Identifying Japanese Knotweed

Japaneses Knotweed (Fallopia japonica) can be seen throughout the entire year and can is commonly found in urban areas, especially on railways, road sides, wasteland and river banks. If spotted it should be left undisturbed as this species can propogate from pieces of root or the stem.

The broad leaves and characteristic ziz-zag pattern associated with the the stem of the Japanese Knotweed.Photo: Japanese Knotweed leaves and Stem (photo by Nigel Mykura - Geograph)

The hollow stems can grow up to 4 m (13.1 ft) in each growing season, although it would be expected to see these as a much reduced height, where they have colonised in urban areas. The leaves are green, shield shaped and have a flat base typically ranging in sizes between 7-14cm long and 5-12cm broad. The leaves which are divided into leaflets are alternate meaning the leaves are not directly opposite each other on the stem. In late summer spiky stems with creamy white flowers can be seen.

Creamy white flowers of the Japanese KnotweedPhoto: Japanese Knotweed flowers (photo by KENPEI)

The characteristic zig-zag pattern stems can be seen throughout the year, varying in colour throughout the seasons. The plant has purple speckled stems in spring/summer, loseing its leaves and dying back in autumn/winter, turning brown in appearance.  The roots are dark and knotty in appearance having a bright orange inside.

Japanese Knotweed StemsPhoto: Japanese Knotweed Stems (photo by Michael Gasperl)

For more information on identifying Japanese Knotweed see the Non-native Species Secretariat website.

More Information

Reporting Invasives

You should record the presence of invasive species on a national database. You can record online at the Non-native Species Secretariat website. You should also alert the appropriate land owner, council and or management body to the presence and location of this plant.