Japanese knotweed Reynoutria japonica


Japanese knotweed is a fast-growing perennial herb. The stems reach up to 3 m in height. It is recorded as being smaller, 0.3-1.5 m in height, in its native range in Japan. Giant knotweed (Fallopia sachalinensis), closely related to Japanese knotweed, grows even taller, up to 4-5 metres, and its leaves are bigger, even over 40 cm in length. The characteristics of Bohemian knotweed (Fallopia × bohemica), a hybrid of Japanese knotweed and giant knotweed, lie somewhere between the stem species.Knotweeds’ stems are glabrous, hollow and slightly woody, often with reddish or reddish-brown flecks. The stems are annual and new ones emerge from the rhizome every year. Large knotweeds therefore produce plenty of litter.

Japanese knotweed thrives in a wide range of habitats. It requires light in order to grow and therefore favours sunny habitats. It also grows in semi-shady sites, such as forest openings and forest edges, but rarely in the actual forest.

Source: FinBIF species descriptions
Description text authors:

Ryttäri, T. SYKE

CC BY 4.0

The map represents observations of this taxon, but it may not be used as a distribution map. A total of

observations in Finland?

FinBIF master checklist
Scientific name
Reynoutria japonica
Vernacular names
  • japanintatar (Finnish)
  • vanligt parkslide (Swedish)
  • Japanese knotweed (English)
Taxon rank
Occurrence in Finland
Collected from Finland
Status in Finland
  • TNV - alien, new, resident
  • 3 - spreading in the wild; completely of cultivated origin
This species is invasive
Administrative status
  • Government Decree on Managing the Risk Caused by Alien Species (704/2019) ?
  • Finland’s National Strategy on Invasive Alien Species (GR 2012) ?
Conservation status in Finland
  • 2019 NA – Not Applicable
  • 2010 NA – Not Applicable
  • Pertti Uotila
Number of public DNA barcode sequences
Due to restrictions in the internatonal BOLD API, we currently cannot show these numbers. ?
Informal groups
  • Vascular plants