Polygonum majus
Wiry knotweed, Wiry Knotweed
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Family: Polygonaceae · Type: Annual · Native
Polygonum majus (Wiry knotweed) is a native California annual in the Polygonaceae family, recognized by large size, large open flowers, and large black fruits.
Wiry knotweed is a California native annual found in the Klamath Ranges, northern Coast Ranges, Cascade Range, Sierra Nevada, and southern Baja Mountains in dry plains and meadows at elevations of 500 to 2,000 meters. Flowering from June to September, this plant produces white or pink flowers in small clusters, with delicate blooms 4 to 5 millimeters long. Growing with erect, wiry green stems 15 to 60 centimeters tall that are slightly angled and papillate-scabrous, it has a distinctive slender form. Its narrow leaves are lance-linear to oblong, 15 to 70 millimeters long, with margins rolled under and fine papillate teeth. The fruit is a small, shiny black elliptic seed 3.5 to 5 millimeters long.
Identification and appearance
Key characters: 26 sympatric species; large size, large open flowers, and large black fruits
Habitat and range
Habitat: dry plains, meadows, serpentine or not
Elevation: 500-2000 m
California counties: El Dorado, Humboldt, Shasta, Siskiyou, Kern, Napa, Alpine, Plumas
Outside California: to British Columbia, Idaho
Bloom period
Polygonum majus blooms Jun-Sep.
How to tell it apart
vs Euphorbia: Polygonum has swollen stem joints with papery sheaths; Euphorbia has milky sap when broken.; vs Persicaria: Hold node sheaths to light—Polygonum's are translucent and split; Persicaria's are opaque and intact.; vs Eriogonum: Polygonum has papery sheaths at nodes; Eriogonum has flowers in cup-like involucres.; vs Acmispon: Polygonum has swollen stem nodes; Acmispon has compound leaves with 3-5 leaflets.; vs Atriplex: Polygonum has papery stem sheaths; Atriplex has mealy or scurfy coating on leaves.
Frequently asked questions
Is Polygonum majus native to California?
Yes. Polygonum majus is native to California (recorded as native).
When does Polygonum majus bloom?
Polygonum majus blooms Jun-Sep.
Where in California does Polygonum majus grow?
Polygonum majus occurs in El Dorado, Humboldt, Shasta, Siskiyou, Kern, Napa, Alpine, Plumas, at elevations of 500-2000 m.
What plant family does Polygonum majus belong to?
Polygonum majus is in the Polygonaceae family, genus Polygonum.
What habitat does Polygonum majus grow in?
Polygonum majus grows in dry plains, meadows, serpentine or not.
Related species
Other California species in the same genus, family, or bioregion.
Sources: Jepson eFlora · Index of California Plant Names · CalPhotos
Last updated 2026-09-30
Data from The California Species Project — 14,000+ California species with verified data from CNPS, CDFW, USFWS, Cal-IPC, and more.