Page author: David Giblin
Polygonum douglasii
Douglas' knotweed, Douglas's knotweed

Distribution: Widely distributed throughout most of Washington; British Columbia south to California, east to the Rocky Mountains and across northern U.S./southern Canada to the Atlantic Coast.

Habitat: Common in dry to moist areas, lowlands to mid-elevations in the mountains.

Flowers: June-September

Origin: Native

Growth Duration: Annual

Conservation Status: Not of concern


A highly variable, simple or freely-branched, erect annual 1-4 dm. tall.


Alternate and numerous along the stem, linear to oblong, lanceolate or even ovate, 1-5 cm. long, sessile, jointed at the base, reduced to bracts above; stipules sheathing, 5-15 mm. long, lacerate.


In loose, elongate racemes and in the leaf axils, 1-4 flowers per node, on pedicles 1-4 mm. long, soon reflexed; perianth 2.5-5 mm. long, the segments greenish with white, pink or reddish margins; stamens 8, occasionally fewer.


Achene with three sharp angles, black, smooth and shining, about 3 mm. long.

Accepted Name:
Polygonum douglasii Greene
Publication: Bull. Calif. Acad. Sci. 1: 125. 1885. 1885.

Synonyms & Misapplications:
Polygonum douglasii Greene ssp. douglasii [JPM]
Polygonum douglasii Greene var. douglasii [HC]
Polygonum douglasii Greene var. latifolium (Engelm.) Greene [HC]
Polygonum emaciatum A. Nelson
Additional Resources:

PNW Herbaria: Specimen records of Polygonum douglasii in the Consortium of Pacific Northwest Herbaria database.

WA Flora Checklist: Polygonum douglasii checklist entry.

E-Flora BC: Polygonum douglasii atlas page.

CalPhotos: Polygonum douglasii photos.

USDA Plants: Polygonum douglasii information.

37 photographs:
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