Persicaria wallichii | Himalayan Knotweed | Glúineach spiceach
Third Schedule listed species under Regulations 49 & 50 in the European Communities (Birds and Natural Habitats) Regulations 2011. (Note: Regulation 50 not yet enacted).
Listed as a schedule 9 species under Articles 15 & 15A of the Wildlife Order (Northern Ireland) 1985 (Article 15A not yet enacted).
Regulated Invasive Alien Species of Union concern under the European Regulation on the prevention and management of the introduction and spread of invasive alien species [1143/2014].
First reported in the wild
Invasive species - risk of Medium Impact
Introduction pathways - 1
Escape from Confinement
Introduction pathways subclass - 1
NAPRA Ireland risk assessed
Tall erect perennial herb, generally occurring in dense patches from 1.5-1.8m tall (Booy et al., 2015), though patches in Poland have been recorded up to 2.2m tall (Bacieczko et al., 2015). Leaves are lanceolate, 8-20cm long (though max 29.9cm in Poland (Bacieczko et al., 2015)), tapering to a point with red veins (Booy et al., 2015).
Due to the formation of dense stands likely to exclude native vegetation but no studies to date on the mechanisms or level of impact.
Woodland, forest and other wooded land; Constructed, industrial or other artificial habitats; Regularly or recently cultivated agricultural, horticultural or domestic habitat; Inland unvegetated or sparsely vegetated habitats; Grasslands and landscapes dominated by forbs, mosses or lichens
Spreads vegetatively when cut or from discarded waste and from sections of rhizome, forms dense stands by vegetative spread (Booy et al., 2015).
Pathway and vector description
Introduced as an ornamental plant in parks and gardens, invading the surrounding area by vegetative spread or through dumping of garden waste (Conolly, 1977).
Mechanism of impact
Primarily found on waste ground, roadsides, railway lines and river banks (Reynolds, 2002).
Established - Widespread, locally abundant. Possibly expanding but this may be an artefact of recording effort. Likely under recorded.
Native to the Himalayas (Preston et al., 2004).
Date of first record category
Fifty year date category
Records submitted to Data Centre in 2023
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How can you help
Report any sightings to the National Biodiversity Data Centre.
Bacieczko, W., Borcz, A., & Kaszycka (2015). Ecological characteristics of Polygonum polystachyum population in North western Poland. Polish Journal of Natural Sciences, 30(1):35-46.
Conolly, A. P. (1977). The distribution and history in the British Isles of some alien species of Polygonum and Reynoutria. Watsonia, 11(4), 291-311.
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.