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smooth cordgrass (spartina alterniflora)


ODA Rating: A, T
Spartina risk assessment
Noxious weed listing process


Oregon smooth cordgrass distribution
Click on image to view larger photo.
S. alterniflora plant
Photo courtesy of V. Howard, PSU-CLR
 Ligule on S. alterniflora
 Photo courtesy of  C. Cornu, South Slough NERR
S. alterniflora mats at Willapa Bay in Washington
Photo courtesy of Tom Forney, ODA
If images are downloaded and used from the ODA web site please be sure to credit the photographer.

This perennial aquatic grass grows erect to 5 feet tall. When fresh, the leaves are flat without prominent midrib and tapers to a sharp tip. Stems are round with joints, hollow between the joints and often red at the base of healthy young plants. The roots are white and fleshy with underground runners (rhizomes) that spread aggressively. Flowers are arranged in compact spikes 10-20cm long, seeds are produced in the fall and can be carried away in water, though viability is usually less than a year. Smooth cordgrass grows on intertidal mud or sand flats that have minimal wave action; it can occur as low as eelgrass beds in the intertidal zone. Smooth cordgrass is similar to common cordgrass (S. anglica), salt-meadow cordgrass (S. patens), and dense-flowered cordgrass (S. densiflora). A detailed key is recommended for positive identification.
Smooth cordgrass is the most dominant non-native cordgrass species in the coastal Pacific Northwest. Inhabiting the lowest intertidal zones in estuaries, this species poses the greatest threat to mudflats crucial to clam and oyster production. Mono-cultures of cordgrass alter estuary hydrology and ecosystem functions through increased sedimentation and accretion, raising the elevation of infested areas several feet. Thousands of acres of mudflats in the Pacific Northwest, critical to migratory waterfowl are at risk of invasion. The largest West Coast infestations are in San Francisco Bay, CA and Willapa Bay, WA.
Distribution in Oregon
Spartina alterniflora; one historic site known form Siuslaw Bay near the Port of Florence. Identified in 1990 and controlled by 1994. Subsequent monitoring found no regrowth until July 2005. A second S. alterniflora site was detected in June 2005 just east of the Charleston marina in Coos Bay. Follow-up indicates unintended transplant of the Spartina from the Florence site to Charleston with native plugs dug for an ODOT mitigation project in Coos Bay. A third site was identified and treated in 2008 by ODA at Young's Bay.
For a collection of spatial information on the distribution of this plant in Oregon go to Oregon WeedMapper.

Biological controls
Biological control agents are not used on "A" listed weeds in Oregon. This weed is being managed for eradication.

Additional information available
The following publications are available through the Oregon Department of Agriculture, Noxious Weed Control Program:
  • The Oregon Spartina Response Plan
  • Key to West Cost Spartina Species
  • Spartina Alterniflora field guide card
To request these items please email Jo Davis, Program assistant