California Invasive Plant Council

Spartina alterniflora x S. foliosa

Common names: smooth hybrid cordgrass

Spartina alterniflora (and S. alterniflora x foliosa hybrids) (smooth cordgrass) is a rhizomatous perennial grass (family Poaceae) found in salt marshes and mudflats in the San Francisco Estuary and associated waterways. Smooth cordgrass spreads more rapidly, grows more densely, and tolerates higher water levels than native California cordgrass (Spartina foliosa). Spartina alterniflora is native to the Atlantic and Gulf coasts of North America. The two cordgrasses are known to hybridize, a process which may threaten the survival of pure strains of California cordgrass. A single smooth cordgrass plant may spread clonally in concentric circles to become a dense circular patch of up to 20 meters in diameter. The invasive cordgrass does not provide suitable habitat for native salt marsh shorebirds.

Cal-IPC Rating: High?

Explanation of Cal-IPC ratings

• High – These species have severe ecological impacts on physical processes, plant and animal communities, and vegetation structure. Their reproductive biology and other attributes are conducive to moderate to high rates of dispersal and establishment. Most are widely distributed ecologically.
• Moderate – These species have substantial and apparent-but generally not severe-ecological impacts on physical processes, plant and animal communities, and vegetation structure. Their reproductive biology and other attributes are conducive to moderate to high rates of dispersal, though establishment is generally dependent upon ecological disturbance. Ecological amplitude and distribution may range from limited to widespread.
• Limited – These species are invasive but their ecological impacts are minor on a statewide level or there was not enough information to justify a higher score. Their reproductive biology and other attributes result in low to moderate rates of invasiveness. Ecological amplitude and distribution are generally limited, but these species may be locally persistent and problematic.
• Alert – An Alert is listed on species with High or Moderate impacts that have limited distribution in California, but may have the potential to spread much further.
• Watch – These species have been assessed as posing a high risk of becoming invasive in the future in California.

CDFA Rating: -*?

Explanation of CDFA ratings

• A – A pest of known economic or environmental detriment and is either not known to be established in California or it is present in a limited distribution that allows for the possibility of eradication or successful containment.
• B – A pest of known economic or environmental detriment and, if present in California, it is of limited distribution.
• C – A pest of known economic or environmental detriment and, if present in California, it is usually widespread.
• D – An organism known to be of little or no economic or environmental detriment, to have an extremely low likelihood of weediness, or is known to be a parasite or predator.
• Q – An organism or disorder suspected to be of economic or environmental detriment, but whose status is uncertain because of incomplete identification or inadequate information.
• * – An asterisk next to the rating indicates that a plant is included in the CCR Section 4500 list of California State Noxious Weeds.
• -* – This plant is included in the CCR Section 4500 list of California State Noxious Weeds, but is otherwise not rated.

More details

Assessment(s)

Plant Assessment Form - Information gathered by Cal-IPC on the impacts, rate of spread, and distribution of invasive plants in California. Does not include management information.

Weed Management Notes

• Management Notes - Information on management techniques and effectiveness from the University of California Cooperative Extension’s Weed Research & Information Center.

Cal-IPC Newsletter Articles

• Hybrid Spartina Forum: Defining eradication for a genetic invader. Hogle, Ingrid. Vol 19, Issue 1
• “Conservation Across Borders” in San Jose. Cal-IPC. Vol 14, Issue 2
• Cordgrass and clapper rails. Grijalva, Erik; Kerr, Drew; Zaremba, Katy. Vol 13, Issue 4
• Invasive Spartina: “Just another weed”: Biology, spread, and prospects for control. Richardson, Brianna. Vol 11, Issue 3

Cal-IPC Symposium Presentations

Presentations are linked where available. Where a presentation is not available, find more information by reading the abstract in the Cal-IPC Symposia Archive.

• Regional partnership to steward San Francisco Bay wetlands. Kerr, Drew (2023)
• California Update. Johnson, Doug (2020)
• Economic impact of selected invasive species: direct costs estimates and economic impacts for Washington State. Haubrich, Greg (2018)
• Washington state’s noxious weed program. Haubrich, Greg (2018)
• Techniques for ecological restoration of Spartina foliosa following local eradication of invasive Spartina alterniflora hybrids. Thornton, Whitney (2014)
• The “other” invasive Spartina in San Francisco Bay: progress towards eradication for the lesser-known species. Kerr, Drew (2014)
• Invasive Spartina Project at a turning point: Eradication on the horizon, reconciling clapper rail impacts, and charting a course towards tidal marsh revegetation with native cordgrass. Kerr, Drew (2011)
• Monitoring a declining, hybridizing weed (7.5 MB). Hogle, Ingrid (2008)
• Self-fertilizing cordgrass hybrids (Spartina alterniflora x S. foliosa) drive local invasion of San Francisco Bay tidal flats. Sloop, Christina M.; Ayres, Debra R.; Strong, Donald R. (2006)
• 2003 Invasive Spartina Project Monitoring Program. Zaremba, K.; McGowan, M.; Ayres, D.R. (2004)
• Behavioral responses of birds to invasive spartina in San Francisco Bay salt marshes. Nordby, J. Cully; Cohen, Andrew N.; Beissinger, Steven R. (2004)
• Invasive hybrid cordgrass (Spartina alterniflora x S. foliosa) recruitment dynamics in open mudflats of San Francisco Bay. Sloop, Christina M.; Ayres, Debra R.; Strong, Donald R. (2004)
• Introduced Spartina in San Francisco Bay: 2000-2001 Survey and Findings, San Francisco Estuary Invasive Spartina Project. Smith, Debra; Klohr, Shannon; Zaremba, Katy (2002)
• Spread of exotic cordgrasses and hybrids (Spartina sp.) in the tidal marshes of San Francisco Bay. Ayres, Debra R.; Smith, Debra L.; Zaremba, Katy; Klohr, Shannon; Strong, Donald R. (2002)

Other Spartina alterniflora x S. foliosa Information

• CalPhotos - Images of plants taken mostly in California.
• Calflora - Distribution map and records of this species in California.
• EDDMapS - Distribution of this species in North America.
• Jepson Interchange - Information on this plant's taxonomy, biology, and distribution from UC Berkeley's Jepson Herbarium.
• USDA PLANTS Database - Information on identification and distribution, with links to websites in individual states.

Additional photos