Page author: David Giblin
Polygonum paronychia
beach knotweed, black knotweed

Distribution: Occurring west of the Cascades crest along the coast; Vancouver Island, B.C., south to Monterey, California.

Habitat: Coastal shorelines and sand dunes.

Flowers: April-September

Origin: Native

Growth Duration: Perennial

Conservation Status: Not of concern


Low, spreading shrub-like perennial here in Washington - typically less than 30 cm., though can get up to 100 cm. tall in some parts of its range.


Alternate, simple, narrow, 1-2 cm long, with prominent midrib.


Small pinkish or whitish, 5-6 mm long, with 5 parts; in small clusters along stem.


Shiny black achenes 4-5 mm long.

Identification Notes:

Can be separated from other Polygonum species by its perennial decumbent stems, lacerate hyaline stipules, axillary flower clusters, and coastal habitat.

Accepted Name:
Polygonum paronychia Cham. & Schltdl.
Publication: Linnaea. 3: 51. 1828. 1828.

Synonyms & Misapplications:
(none provided)
Additional Resources:

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

WA Flora Checklist: Polygonum paronychia checklist entry.

E-Flora BC: Polygonum paronychia atlas page.

CalPhotos: Polygonum paronychia photos.

USDA Plants: Polygonum paronychia information.

19 photographs:
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