Polygonum sawatchense
Knotweed
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Family: Polygonaceae · Type: Annual · Native
Polygonum sawatchense (Knotweed) is a native California annual in the Polygonaceae family.
Knotweed is a California native annual found in rocky or disturbed habitats at elevations from 1,500 to 2,500 meters. Flowering from July to September, this plant produces tiny green to reddish-purple flowers with white or pink margins, clustered in spike-like inflorescences. Growing with erect stems 10 to 40 centimeters tall, the plant has slender green to brownish stems that are slightly angled and sometimes papillate-scabrous. Its narrow linear to oblanceolate leaves are 8 to 45 millimeters long, with margins rolled under or flat and acute tips. The small black, shiny fruits are elliptic and nestled within the plant's flower clusters.
Identification and appearance
Key characters: Geographically isolated with no sympatric species
Habitat and range
California counties: Alpine, Lassen, Plumas, Tulare, Shasta, Tuolumne, Mono, Trinity, San Bernardino, Fresno, Siskiyou, Ventura, Riverside, Sierra, Inyo, Modoc
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 sawatchense native to California?
Yes. Polygonum sawatchense is native to California (recorded as native).
Where in California does Polygonum sawatchense grow?
Polygonum sawatchense occurs in Alpine, Lassen, Plumas, Tulare, Shasta, Tuolumne, Mono, Trinity and other counties.
What plant family does Polygonum sawatchense belong to?
Polygonum sawatchense is in the Polygonaceae family, genus Polygonum.
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.