Page authors: Don Knoke, David Giblin
Polygonum spergulariiforme
fall knotweed, spurry knotweed

Distribution: Occurring west of the Cascades crest and east in the Columbia River Gorge in Washington; British Columbia to California, east to Idaho, Montana, and Wyoming.

Habitat: Balds, prairies, and headlands in gravelly, sandy or heavy, dry or moist soil at low elevations.

Flowers: June-September

Origin: Native

Growth Duration: Annual

Conservation Status: Not of concern


Erect to rounded annual, the stems simple or freely-branched, up to 5 dm. tall, the branches wiry, sharply angled above.


Leaves alternate, basally jointed, linear to narrowly oblong-oblanceolate, 1-3 cm. long and 1-2 mm. wide; stipules sheathing, lacerate, 3-6 mm. long.


Flowers 1-4 in the axils of the upper leaves and crowded, leaf-like bracts which exceed the flowers; pedicles slender, 1-2 mm. long; the 5 perianth segments 3-4 mm. long, attached 1/3 their length, pinkish with a green midrib; stamens 8; styles 3, 0.5 mm. long.


Achene 3-angled, 3-4 mm. long, black, shining and smooth.

Accepted Name:
Polygonum spergulariiforme Meisn. ex Small
Publication: Bull. Torrey Bot. Club. 19: 366. (as spergulariaeforme). 1892.

Synonyms & Misapplications:
Polygonum douglasii Greene ssp. spergulariiforme (Meisn. ex Small) J.C. Hickman [JPM, ILBC4]
Polygonum spergulariaeforme Meisn. ex Sm., orthographic variant [HC]
Additional Resources:

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

WA Flora Checklist: Polygonum spergulariiforme checklist entry.

E-Flora BC: Polygonum spergulariiforme atlas page.

CalPhotos: Polygonum spergulariiforme photos.

USDA Plants: Polygonum spergulariiforme information.

20 photographs:
Group by