Page authors: Don Knoke, David Giblin
Persicaria hydropiperoides
water pepper, swamp smartweed

Distribution: Occurring chiefly west of the Cascades crest in Washington; British Columbia to Mexico and South America, east across North America to the Atlantic coast.

Habitat: Moist to swampy areas, often growing in mud, from the lowlands to the lower mountain valleys.

Flowers: July-September

Origin: Native

Growth Duration: Perennial

Conservation Status: Not of concern

Pollination: Bees, flies


Herbaceous perennial, up to 1 m. tall, usually decumbent and tending to root freely.


Leaves numerous on short petioles, alternate, scarcely reduced upward, lanceolate to oblong-lanceolate with an acute base, 5-12 cm. long; sheathing stipules 1-2 cm. long with bristly hairs around the top.


Inflorescence of 2 or more spike-like, interrupted racemes; perianth greenish to white or pinkish, 2.5-3 mm. long, 5-lobed half the length, the segments oblong and sub-equal; stamens 8 with short filaments


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

Accepted Name:
Persicaria hydropiperoides (Michx.) Small
Publication: Fl. S.E. U.S. 378. 1903.

Synonyms & Misapplications:
Persicaria opelousana (Riddell ex Small) Small
Persicaria paludicola Small
Polygonum hydropiperoides Michx. [HC, ILBC4, JPM]
Polygonum hydropiperoides Michx. var. adenocalyx (Stanford) Gleason
Polygonum hydropiperoides Michx. var. asperifolium Stanford
Polygonum hydropiperoides Michx. var. breviciliatum Fernald
Polygonum hydropiperoides Michx. var. buschianum Stanford
Polygonum hydropiperoides Michx. var. digitatum Fernald
Polygonum hydropiperoides Michx. var. hydropiperoides [HC]
Polygonum hydropiperoides Michx. var. opelousanum (Riddell ex Small) W. Stone
Polygonum hydropiperoides Michx. var. psilostachyum H. St. John
Polygonum opelousanum Riddell ex Small
Polygonum opelousanum Riddell ex Small var. adenocalyx Stanford
Additional Resources:

PNW Herbaria: Specimen records of Persicaria hydropiperoides in the Consortium of Pacific Northwest Herbaria database.

WA Flora Checklist: Persicaria hydropiperoides checklist entry.

OregonFlora: Persicaria hydropiperoides information.

E-Flora BC: Persicaria hydropiperoides atlas page.

CalPhotos: Persicaria hydropiperoides photos.

USDA Plants: Persicaria hydropiperoides information.

17 photographs:
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