Fallopia japonica x sachalinensis = F. x bohemica | Glúineach bhiorach



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.

First reported in the wild



Invasive species - risk of High Impact

Irish status


Introduction pathways - 1


Invasive score


NAPRA Ireland risk assessed


Species Biology


Tall, vigorous herbaceous perennial, growing in dense patches, generally 2-3 but up to 4m tall (taller than F. japonica but shorter than F. sachalinensis), with green bamboo like stems (Booy et al., 2015). Leaves shield shaped with a heart shaped based, 20-25cm long, with short stout hairs on the underside (Booy et al., 2015). See also Fallopia japonica and Fallopia sachalinensis.


Lowers biodiversity by crowding out native plants. Riparian habitats invaded by knotweeds have lower invertebrate abundance, species richness and biomass, 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 allepathic 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


Highly variable pollen production and viability ranging from 500 to 7000 pollen grains per flower and 3–48 % respectively (Tiébré et al., 2007), though seed production is rarely recorded in the UK (Bailey et al., 2009).

Pathway and vector description

Naturally occurring hybrid of two invasive species, F. japonica and F. sachalinensis, though may have also been sold as an ornamental plant (Reynolds, 2002). Thought to be in cultivation in Britain since the 19th century and present in the wild there since 1954, it was not described until 1983 making it difficult to ascertain a precise history of its introduction and spread (Bailey & Connolly, 2000; Preston et al., 2004; Reynolds, 2002).

Mechanism of impact

Competition, Bio-fouling

Broad environment


Habitat description

Found in a wide variety of habitats though particular established and persistent on urban waste ground, roadsides and river banks (Preston et al., 2004; Reynolds, 2002).

Species group


Native region


Similar species

Fallopia japonica, Fallopia sachalensis 


World distribution(GBIF)

Irish distribution

Established - Widespread & Locally abundant. Likely under recorded due to confusion over identification with F. japonica.

Native distribution

Hybrid of two non-native species arising in Europe.

Temporal change

Date of first record category


Fifty year date category


Records submitted to Data Centre in 2022

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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

Global Invasive Species Database

CABI Datasheet