Polygonum bidwelliae
Bidwell's knotweed
(c) Steve Matson, some rights reserved (CC BY) · licence
Family: Polygonaceae · Type: Herb · Native
Conservation status: CNPS 4.3
Polygonum bidwelliae (Bidwell's knotweed) is a native California herb in the Polygonaceae family, recognized by distinctive overlapping ocreae obscuring leaves and flowers.
Bidwell's knotweed is a California native annual found in northern California's Butte, Tehama, and Shasta counties in volcanic chaparral, montane woodland valleys, and grasslands at elevations of 60 to 1,200 meters. Flowering from May to June, this delicate plant produces small pink flowers with white margins, each blossom nestled discretely in the plant's upper leaf axils. Growing with slender, wiry green stems 2 to 20 centimeters tall that are minutely rough-textured and slightly angled, the plant forms a compact, sparse structure. Its narrow linear leaves are remarkably small, measuring 5 to 15 millimeters long and less than 2 millimeters wide, with tightly rolled margins and spine-tipped ends that create a distinctive fine-toothed appearance. The fruits are shiny light-brown to brown, small ovate-elliptic structures that remain enclosed within the plant's delicate structure.
Identification and appearance
Key characters: 23 sympatric species; distinctive overlapping ocreae obscuring leaves and flowers
Habitat and range
Habitat: Thin volcanic soils, chaparral, montane woodland valleys, grassland
Elevation: 60-1200 m
California counties: Butte, Shasta, Tehama
Bloom period
Polygonum bidwelliae blooms May-Jun.
Conservation status
CNPS 4.3
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 bidwelliae native to California?
Yes. Polygonum bidwelliae is native to California (recorded as native).
When does Polygonum bidwelliae bloom?
Polygonum bidwelliae blooms May-Jun.
Where in California does Polygonum bidwelliae grow?
Polygonum bidwelliae occurs in Butte, Shasta, Tehama, at elevations of 60-1200 m.
What plant family does Polygonum bidwelliae belong to?
Polygonum bidwelliae is in the Polygonaceae family, genus Polygonum.
Is Polygonum bidwelliae rare or endangered?
Polygonum bidwelliae carries California Rare Plant Rank 4.3, state rank S4.
Related species
Other California species in the same genus, family, or bioregion.
Sources: Jepson eFlora · CNPS Rare Plant Inventory · Index of California Plant Names · CalPhotos · CDFW CNDDB
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.