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© Lamiot
© Gilles San Martin
© Marcel Blok
© Emmanuel Delbart, FUSAGx
Koenigia polystachya - Himalayan knotweed

Synonym: Polygonum polystachyum, Persicaria wallichii
French name:  Renouée de l'himalaya
Dutch name: Afgaanse duizendknoop
Family: Polygonaceae
Group: Vascular plants
Origin: Asia
Habitat: terrestrial
Introduction:  agri- and horticulture
ISEIA Score : 10
Naturalization in Belgium
First observation in the wild: 1898
Invasion stage: naturalization
Spatial distribution: restricted
Reproduction in the wild: yes
Dispersion potential: high
Natural habitats: medium
More on invasiveness: Himalayan knotweed thrives on moist nutrient-rich soils, in various light conditions. It is mostly found in ruderal and waste areas but can also develop in wetlands and in riparian habitats. In North America, the plant is known to survive severe floods and is able to rapidly colonize shores and islands. It fragments easily, spreads most often by vegetative means and can be carried by floodwater. Even very small fragments can form new plants. It is commonly used as an ornamental and is planted in gardens and public green areas.
Distribution in Belgium
Established populations
absent from district
isolated populations (1-5 localities per district)
widespread (>5 localities per district)
Endangered areas
low risk
medium risk
high risk

Endangered Natura 2000 habitats ():
grasslands: 6430
Impacts on Species
Predation / Herbivory: low
Competition: high
Disease transmission: low
Genetic effects: low
Impacts on Ecosystems
Nutrient cycling: likely
Physical alteration: likely
Natural successions: medium
Food web alteration: low
More on impacts: P. wallichii grows vigorously and creates large, dense and persistent colonies that exclude native vegetation and prevents the establishment of tree seedlings. It also favours erosion of river banks and greatly alter natural ecosystems. Colonies are difficult to eradicate.
Data Source & References
Authors: Branquart Etienne, Vanderhoeven Sonia, Van Landuyt Wouter, Van Rossum Fabienne, Verloove Filip
Published on:  04 December 2007
Last update:  06 July 2018
AEF (2006)
Cartes provisoires de la distribution de néophytes en Wallonie.
Unpublished document.
CPS-SKEW (2006)
Polygonum polystachium.
From online fact sheets of the Swiss Commission for Wild Plants Conservation
Hill, M. et al. (2009)
Developing an indicator of the abundance, extent and impact of invasive non-native species. Final report.
Defra, 49pp. (WC0718)
Lambinon, J., Delvosalle, L. & Duvigneaud, J. (2004)
Nouvelle fore de la Belgique, du Grand-Duché de Luxembourg, du Nord de la France et des régions voisines.
Editions du Patrimoine du Jardin botanique national de Belgique, Meise.
Van Landuyt, W., Hoste, I., Vanhecke, L., Van den Bremt, P. Vercruysse, W. & De Beer, D. (2006)
Atlas van de Flora van Vlaanderen en het Brussels gewest.
Nationale Plantentuin en het Instituut voor Natuur- en Bosonderzoek i.s.m. Flo.Wer vzw.
Verloove, F. (2006)
Catalogue of the Neophytes in Belgium (1800-2005).
Scripta Botanica Belgica 39, 89 pp.
Wittenberg, R. (2005)
An inventory of alien species and their threat to biodiversity and economy in Switzerland.
CABI Bioscience Switzerland Centre report to the Swiss Agency for Environment, Forests and Landscape. The environment in practice no. 0629: 155p.

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