Polygonum californicum
California knotweed
(c) Adam J. Searcy, some rights reserved (CC BY) · licence
Family: Polygonaceae · Type: Herb · Native
Polygonum californicum (California knotweed) is a native California herb in the Polygonaceae family, recognized by open flowers and papillate-dentate leaf margins.
California knotweed is a California native annual found in northwestern California, Cascade Range, Sierra Nevada, Central Valley, and southwestern Mountain Provinces in open places, including serpentine habitats, at elevations of 40 to 1,200 meters. Flowering from May to October, this plant produces delicate white to pink flowers with elliptic lobes in small axillary clusters. Growing with wiry, green stems 4 to 40 centimeters tall that are slightly angled and papillate-scabrous, it has an erect or widely spreading growth habit. Its linear leaves are extremely narrow, measuring 5 to 25 millimeters long and only 0.5 to 2 millimeters wide, with margins rolled under and a mucronate or weakly spine-tipped apex. The fruit is a shiny brown, narrowly elliptic structure 1.8 to 2.2 millimeters long.
Identification and appearance
Key characters: 26 sympatric species; open flowers and papillate-dentate leaf margins
Habitat and range
Habitat: Open places (including serpentine)
Elevation: 40-1200 m
California counties: Mendocino, Butte, Tuolumne, Napa, Shasta, Lake, El Dorado, Placer, Amador, Fresno, Tehama, Madera, Mono, Siskiyou, Tulare, Yolo, Yuba, Sacramento, Calaveras, Glenn, Mariposa, Nevada, San Francisco, San Joaquin, Stanislaus, Sutter, Trinity, Sonoma, Humboldt, Lassen, Plumas
Outside California: to Washington
Bloom period
Polygonum californicum blooms May-Oct.
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 californicum native to California?
Yes. Polygonum californicum is native to California (recorded as native).
When does Polygonum californicum bloom?
Polygonum californicum blooms May-Oct.
Where in California does Polygonum californicum grow?
Polygonum californicum occurs in Mendocino, Butte, Tuolumne, Napa, Shasta, Lake, El Dorado, Placer and other counties, at elevations of 40-1200 m.
What plant family does Polygonum californicum belong to?
Polygonum californicum is in the Polygonaceae family, genus Polygonum.
What habitat does Polygonum californicum grow in?
Polygonum californicum grows in Open places (including serpentine).
Related species
Other California species in the same genus, family, or bioregion.
Sources: Jepson eFlora · Index of California Plant Names · CalPhotos
Last updated 2026-10-07
Data from The California Species Project — 14,000+ California species with verified data from CNPS, CDFW, USFWS, Cal-IPC, and more.