Taxon Report

Polygonum marinense Mertens & Raven

Marin knotweed

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Taxon Summary

Polygonum marinense, commonly known as Marin knotweed, is a annual herb in the Polygonaceae that is found only in California. It occurs within Marshes and swamps (brackish, and coastal salt), growing at elevations from 0 to 10 meters. Polygonum marinense is ranked 3.1, Plants About Which We Need More Information, A Review List; Seriously threatened in California.

  Classification
Scientific Name:
 Polygonum marinense Mertens & Raven
Common Name:
 Marin knotweed
Family: Polygonaceae
Element Code: PDPGN0L1C0
USDA Plants Symbol: POMA15
Synonyms/Other Names:

Ecology and Life History
Lifeform: annual herb
Blooming Period: (Apr)May-Aug(Oct) (Apr)May-Aug(Oct)
Elevation: 0-10 (0-35)
General Habitats: Marshes and swamps
Microhabitat:
Microhabitat Details:

Conservation Status
CA Rare Plant Rank: 3.1
Global Rank: G2Q
State Rank:
 S2
State List: None
Fed List: None
Other Status:
CRPR Changes:
  • changed from 3.1 to 3.1 on 2008-07-14

Occurrence Data from the CNDDB
Total Occurrences: 32
Element Occurrence Ranks:
   Excellent (A) 2
   Good (B) 13
   Fair (C) 9
   Poor (D) 0
   None (X) 0
   Unknown (U) 8

Location
California Endemic:  True
California Counties and Islands: Name (Code)
Alameda (ALA), Contra Costa (CCA), Marin (MRN), Napa (NAP), San Francisco (SFO), Solano (SOL), Sonoma (SON)
Quads: Name (Quad Code)
Benicia (3812212), Bodega Head (3812331), Cuttings Wharf (3812223), Drakes Bay (3812218), Hunters Point (3712263), Inverness (3812217), Oakland East (3712272), Oakland West (3712273), Petaluma Point (3812214), Petaluma River (3812225), San Leandro (3712262), San Rafael (3712285), Tomales (3812228)

Threat List Data from the CNDDB

Threat List Total: 9
EOs with Threat Listed: Total EOs % of EOs
17 53 %
Grazing 14 43%
Foot traffic/trampling 9 28%
Altered flood/tidal/hydrologic regime 2 6%
Development 1 3%
Erosion/runoff 1 3%
Non-native plant impacts 1 3%
Other 1 3%
Recreational use (non-ORV) 1 3%
Vandalism/dumping/litter 1 3%

Notes
Move to List 1B? Known from fewer than twenty occurrences. Taxonomic status uncertain, related to P. aviculare; possibly synonym of P. robertii, a non-native plant. Immediate taxonomic study needed. Threatened by coastal development and foot traffic.
Threats:
Taxonomy:

Selected References

CRPR List Change on 2008-07-14
Citation California Native Plant Society, Rare Plant Program. 2025. Rare Plant Inventory (online edition, v9.5.1). Website https://www.rareplants.cnps.org [accessed 27 January 2025].