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Reynoutria japonica Houtt.
Family Polygonaceae
Common name: Japanese Knotweed

Reynoutria japonica Houtt. APNI*

Synonyms: Fallopia japonica (Houtt.) Ronse Decr. APNI*
Polygonum cuspidatum Sieber & Zucc. APNI*
Tiniaria japonica APNI*
Polygonum cuspidatum var. compactum APNI*

Description: Perennials 1.5–3 m high, forming a dense thicket. Stems annual, robust, bamboo-like, often glaucous and red-brown, numerous and branched above, dying back in winter.

Leaves broad-ovate, 5–15 cm long, 2–12 cm wide, glabrous, with the apex long-acuminate to cuspidate, the base truncate.

Flowers in clusters of 2–4, in paniculate inflorescences with slender, rather lax branches; perianth segments greenish to creamy white, the outer 3 developing broad wings at maturity.

Achene 2–4 mm long, glossy, dark brown to blackish.

Photo Picturae


Distribution and occurrence: Cultivated in gardens, occasionally persistent on old garden sites or naturalised in temperate areas of SE Australia (? Cooma, ?Albury; Victoria, Tasmania). Native of Korea, Japan, Taiwan and eastern mainland China. Cultivated in Europe and North America but now considered a problem weed there. Hybridizes readily with R. sacchalinenis; the hybrid is known as R. x bohemica.
NSW subdivisions: *ST, *SWS, *SWS
Other Australian states: *Tas. *Vic.
AVH map***

Previously treated as Fallopia japonica or Polygonum cuspidatum. It hybridises with R. sachalinensis, and that hybrid (R. x bohemica) is also in Australia. These giant knotweeds are potentially serious weeds in cooler climate regions of Australia.

Text by K. L. Wilson (1990); edited KL Wilson (Jan 2008, July 2009, Sept 2017)
Taxon concept: Flora of NSW 1 (1990)

APNI* Provides a link to the Australian Plant Name Index (hosted by the Australian National Botanic Gardens) for comprehensive bibliographic data
***The AVH map option provides a detailed interactive Australia wide distribution map drawn from collections held by all major Australian herbaria participating in the Australian Virtual Herbarium project.
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