E-Flora BC: Electronic Atlas of the Flora of British Columbia

Reynoutria japonica (Houtt.) Ronse Decr. var. japonica
Japanese knotweed
Polygonaceae (Buckwheat family)

Introduction to Vascular Plants
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Distribution of Reynoutria japonica var. japonica
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Species Information

Perennial herb from a rhizome; stems erect, numerous, branched, 1-3 m tall, reddish-brown.
Basal leaves lacking; stem leaves alternate, 10-15 cm long, the blades egg-shaped to more or less round, the bases rounded or squared off, the tips abruptly pointed, long stalked; stipules short, tubular, entire, usually deciduous.
Inflorescence of numerous flowers in many panicles; perianths whitish or greenish-white, about 2 mm long at anthesis, 5-lobed nearly to the base.
Achenes, 3-angled, black, smooth and shiny, 2.5-3 mm long.
Easily confused with P. sachalinense.

Source: The Illustrated Flora of British Columbia

Habitat / Range

Moist to mesic ditches and disturbed sites in the lowland zone; frequent in the lower Fraser Valley, rare in the Queen Charlotte Islands, Powell River and SC BC; introduced from Asia.

Source: The Illustrated Flora of British Columbia

Synonyms and Alternate Names

Fallopia japonica

Taxonomic and Nomenclatural Links

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General References