Polygonum marinense
Marin knotweed
Family: Polygonaceae · Type: Herb · Native
Conservation status: CNPS 3.1
Polygonum marinense (Marin knotweed) is a native California herb in the Polygonaceae family, recognized by restricted coastal marsh habitat and broad elliptic leaves.
Marin knotweed is a California native annual found in northern coastal counties including Marin, Napa, Solano, and Sonoma in coastal salt and brackish marshes at elevations below 10 meters. Flowering from April to August, this plant produces white to pink flowers in small clusters, with each flower approximately 3 to 3.5 millimeters long. Growing with prostrate to ascending succulent stems 15 to 40 centimeters long that range from green to red-tinged, it has distinctive ribbed branches emerging from the base. Its leaves are elliptic to obovate, generally 20 to 35 millimeters long with a rounded tip, often displaying a reddish tinge along the margins. The fruit is small, shiny brown, and ovate, measuring 2.8 to 3.4 millimeters long and developing late in the season.
Identification and appearance
Key characters: 11 sympatric species; restricted coastal marsh habitat and broad elliptic leaves
Habitat and range
Habitat: Coastal salt, brackish marshes, swamps
Elevation: < 10 m
Bloom period
Polygonum marinense blooms Apr-Aug.
Conservation status
CNPS 3.1
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 marinense native to California?
Yes. Polygonum marinense is native to California (recorded as native).
When does Polygonum marinense bloom?
Polygonum marinense blooms Apr-Aug.
What plant family does Polygonum marinense belong to?
Polygonum marinense is in the Polygonaceae family, genus Polygonum.
Is Polygonum marinense rare or endangered?
Polygonum marinense carries California Rare Plant Rank 3.1, state rank S2.
What habitat does Polygonum marinense grow in?
Polygonum marinense grows in Coastal salt, brackish marshes, swamps.
Related species
Other California species in the same genus, family, or bioregion.
Sources: Jepson eFlora · 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.