Fallopia sachalinensis | Giant Knotweed | Glúineach chapaill



Conservation status

Not Assessed

Legal status

Third Schedule listed species under Regulations 49 & 50 in the European Communities (Birds and Natural Habitats) Regulations 2011. (Note: Regulation 50 not yet enacted). Vector materials for this species (soil or spoil taken from infested sites) are also covered under Regulations 49 & 50. Listed as a schedule 9 species under Articles 15 & 15A of the Wildlife Order (Northern Ireland) 1985 (Article 15A not yet enacted).

First reported in the wild



Invasive species - risk of High Impact

Irish status


Introduction pathways - 1

Escape from Confinement

Introduction pathways subclass - 1

Ornamental purpose

Invasive score


NAPRA Ireland risk assessed


Species Biology


Tall, vigorous herbaceous perennial, growing in dense patches though not as dense as other Fallopia spp, generally 2-3 but up to 5m tall (much taller than F. x bohemica & F. japonica), with green bamboo like stems (Booy et al., 2015). Leaves up to 40cm long, oval or oblong with long wavy hairs on the underside (Booy et al., 2015). See also Fallopia japonica and Fallopia x bohemica.


Lowers biodiversity by crowding out native plants. Riparian habitats invaded by knotweeds have lower invertebrate abundance, species richness and biomass and lower plant species richness compared to uninvaded sites, which is likely to impact on amphibians, reptiles, birds and mammals that use riparian habitats (Gerber et al., 2014). Has been shown to exert allopathic effects (releases chemicals into the soil that inhibit the growth of other plants) in common riparian plants such as nettles (Urtica dioica) (Moravcová et al., 2011).


Mires, bogs & fens; Heath, scrubland & tundra; Woodland, forest and other wooded land; Regularly or recently cultivated agricultural, horticultural or domestic habitat; Inland unvegetated or sparsely vegetated habitats; Constructed, industrial or other artificial habitats, Miscellaneous


High pollen production of between 7000 & 8000 pollen grains per flower (Tiébré et al., 2007).

Pathway and vector description

Commercially available to gardeners in the UK since the 1870s (Bailey & Connolly, 2000), though less widely sold than F. japonica due to its large size. Naturalised in Ireland before 1896 (Reynolds, 2002), generally planted in estates and botanical gardens (Bailey & Connolly, 2000; Reynolds, 2002).

Mechanism of impact

Competition, Bio-fouling

Broad environment


Habitat description

Generally found as relics of cultivation in parks or botanic gardens, though also found on waste ground, roadsides and river banks (Preston et al., 2004; Reynolds, 2002).

Species group


Native region

Temperate Asia

Similar species

Fallopia japonica,  Fallopia x bohemica


World distribution(GBIF)

Irish distribution

Established - Widespread but localised

Native distribution

Native to Japan and Sakhalin (Preston et al., 2004).

Temporal change

Date of first record category


Records submitted to Data Centre in 2021

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How can you help

Report any sightings to the National Biodiversity Data Centre.



Bailey, J. P., & Conolly, A. P. (2000). Prize-winners to pariahs-a history of Japanese knotweed sl (Polygonaceae) in the British Isles. Watsonia, 23(1), 93-110.

Booy, O., Wade, M. & Roy, H. (2015) A Field Guide to Invasive Plants & Animals in Britain. Bloomsbury.

Gerber, E., Krebs, C., Murrell, C., Moretti, M., Rocklin, R., & Schaffner, U. (2008). Exotic invasive knotweeds (Fallopia spp.) negatively affect native plant and invertebrate assemblages in European riparian habitats. Biological Conservation, 141(3), 646-654.

Moravcová, L., Pyšek, P., Jarošik, V., & Zákravský, P. (2011). Potential phytotoxic and shading effects of invasive Fallopia (Polygonaceae) taxa on the germination of native dominant species. NeoBiota, 9, 31-47.

Preston, C.D., Pearman, D. A. & Dines, T. D. 2002. New atlas of the British and Irish flora. An atlas of the vascular plants of Britain, Ireland, the Isle of Man and the Channel Islands, Oxford University Press.

Reynolds, S.C.P. (2002) A catalogue of alien plants in Ireland. National Botanic Gardens. Glasnevin, Dublin.

Stace, C. (1997). New Flora of the British Isles 2nd Edition. Cambridge University Press, Cambridge.

Tiébré, M. S., Vanderhoeven, S., Saad, L., & Mahy, G. (2007). Hybridization and sexual reproduction in the invasive alien Fallopia (Polygonaceae) complex in Belgium. Annals of Botany, 99(1), 193-203.

DAISIE Factsheet

CABI Datasheet