Polygonum paronychia
Beach knotweed
(c) Tom Hilton, some rights reserved (CC BY) · licence
Family: Polygonaceae · Type: Subshrub · Native
Polygonum paronychia (Beach knotweed) is a native California subshrub in the Polygonaceae family, recognized by coastal habitat, rooting stems, and large pink/white flowers.
Beach knotweed is a California native perennial found in coastal bioregions including Northern and Central Coast in coastal dunes and scrub habitats at elevations below 50 meters. Flowering from March to September, this plant produces delicate pink or white flowers in small clusters, with blooms turning red-brown when dry. Growing with prostrate or ascending stems 10 to 100 centimeters long that root at nodes, it has a distinctive leathery appearance with brown, angled branches. Its leaves are crowded toward stem tips, linear to oblanceolate, 10 to 20 millimeters long with margins rolled under and acute tips. The fruit is a shiny black, ovate structure approximately 4 to 5 millimeters long.
Identification and appearance
Key characters: 22 sympatric species; coastal habitat, rooting stems, and large pink/white flowers
Habitat and range
Habitat: Coastal dunes, scrub
Elevation: < 50 m
California counties: Humboldt, Mendocino, San Francisco, Marin, San Mateo, Monterey, Del Norte, Sonoma, San Luis Obispo, Santa Cruz
Outside California: to British Columbia
Bloom period
Polygonum paronychia blooms Mar-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 paronychia native to California?
Yes. Polygonum paronychia is native to California (recorded as native).
When does Polygonum paronychia bloom?
Polygonum paronychia blooms Mar-Sep.
Where in California does Polygonum paronychia grow?
Polygonum paronychia occurs in Humboldt, Mendocino, San Francisco, Marin, San Mateo, Monterey, Del Norte, Sonoma and other counties, at elevations of < 50 m.
What plant family does Polygonum paronychia belong to?
Polygonum paronychia is in the Polygonaceae family, genus Polygonum.
What habitat does Polygonum paronychia grow in?
Polygonum paronychia grows in Coastal dunes, scrub.
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.