Common name: Japanese knotweed
Synonyms: Reynoutria japonica, Polygonum cuspidatum
Plant type: Herbaceous
Life cycle: Perennial
Code of conduct: Annex I (consensus list)
Invasive status (ISEIA protocol): Black list
Main ornemental function: Mixed border • Cover ground
This factsheet is common for 3 Fallopia species listed as invasive : Fallopia japonica, F. sachalinensis, F. x bohemica. F. japonica is one of the most common invasive knotweeds, recognizable with leaves flattened at the base. Herbaceous perennial with robust, erect stems with distinct nodes like bamboo, up to 4 m tall and an extensive system of rhizomes. These rhizomes can be 15-20 m long and can penetrate to 3 - 7 m deep in the soil. White flowers.
High vegetative multiplication capacities. Strong aptitudes of lateral expansion by rhizomes: rhizomes can spread up to 1 m/year. Small rhizomes fragments of a few grammes can regenerate the whole plant. Rhizome fragments can be dispersed over long distances through rivers or soil transports. Stems fragments can also regenerate the plant, specially from the nodes. The plant grows fastly. Human-transported soil contaminated with rhizomes is the major dispersal vector. Sexual reproduction may also occurs, but is less frequent. In Belgium, seedlings of knotweeds are rarely observed in nature.
Fallopia species can grow in a wide array of habitats, with a preference for wet, nitrogen-rich soils e.g. river banks and alluvial zones. Also frequenlty found along railways and roads.
Species classified A3 in Belgium. Knotweeds are recognized as aggressive invaders throughout Western, Central and Northern Europe. Fallopia japonica is classified as one of the 100 worst invasive plants in Europe. This plant forms very dense populations which outcompete native vegetation, reduce species richness and modify soil properties. Fallopia species produce allelopathic substances which inhibit the growth of native species. Soil nutrient cycling is also modified in invaded areas. Due to its high growing rate and vegetative multiplication capacities, management of Fallopia populations is very difficult. Stands of knotweed along rivers encourage bank erosion. Prolific rhizome and shoot growth can damage infrastructures like foundations, walls, etc For more information about this species, click here
Do not plant, do not buy this species.
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