Spartina alterniflora
(smooth cordgrass)

Preferred Common Name

• smooth cordgrass

International Common Names

• English: Atlantic cordgrass; saltmarsh cordgrass; salt-water cordgrass

• Domain: Eukaryota
•     Kingdom: Plantae
•         Phylum: Spermatophyta
•             Subphylum: Angiospermae
•                 Class: Monocotyledonae
•                     Order: Cyperales
•                         Family: Poaceae
•                             Genus: Spartina
•                                 Species: Spartina alterniflora

Spartina is a relatively small genus consisting of approximately 14 species, geographically centered along the east coast of North and South America, with outliers on the west coast of North America, Europe, and Tristan da Cunha. Members of the genus occur primarily in wetlands, especially estuaries (Partridge, 1987).

S. alterniflora is a rhizomatous perennial grass that grows initially in round, genetically similar, clumps ranging between 0.5-3m in height, eventually forming extensive monoculture meadows. The stems are hollow and hairless. The leaf blades are 3 to 25 mm wide. The leaves lack auricles and have ligules (1-2 mm) that consist of a fringe of hairs. The flowers (classified yellow, although visually seem white) are inconspicuous and are borne in greatly congested spikes, 2-5 cm long (Hitchcock et al., 1969). Along its introduced east coast range S. alterniflora flowers between late August and September. The plant is deciduous; its stems die back at the end of each growing season (Ebasco Environmental, 1992; Daehler and Strong, 1994).

Within its native range of the Atlantic and Gulf coastlines of USA, S. alterniflora exhibits two growth forms, at different salt marsh zones. A tall form occurs along creek banks and drainage channels. Landward of the tall form, an intermediate form occurs, which grades into a stunted form at the salt marsh interior (Smart, 1982).

A detailed description of S. alterniflora is provided by the Grass Manual on the Web (http://herbarium.usu.edu/).

Plants rhizomatous; rhizomes elongate, flaccid, white, scales inflated, not or only slightly imbricate. Culms to 250 cm tall, (0.3) 5-15(20) mm thick, erect, solitary or in small clumps, succulent, glabrous, having an unpleasant, sulphurous odor when fresh. Sheaths mostly glabrous, throat glabrous or minutely pilose, lower sheaths often wrinkled; ligules 1-2 mm; blades to 60 cm long, 3-25 mm wide, lower blades shorter than those above, usually flat basally, becoming involute distally, abaxial surfaces glabrous, adaxial surfaces glabrous or sparsely pilose, margins usually smooth, sometimes slightly scabrous, apices attenuate. Panicles 10-40 cm, with 3-25 branches, often partially enclosed in the uppermost sheath; branches 5-15 cm, loosely appressed, not twisted, more or less equally subremote to moderately imbricate throughout the panicle, axes often prolonged beyond the distal spikelets, with 10-30 spikelets. Spikelets 8-14 mm, straight, usually divergent, more or less equally imbricate on all the branches. Glumes straight, sides usually glabrous, sometimes pilose near the base or appressed pubescent, hairs to 0.3 mm; lower glumes 4-10 mm, acute; upper glumes 8-14 mm, keels glabrous, lateral veins not present, apices acuminate to obtuse, occasionally apiculate; lemmas glabrous or sparsely pilose, apices usually acuminate; paleas slightly exceeding the lemmas, thin, papery, apices obtuse or rounded; anthers 3-6 mm. 2n = 62.

The initial date and method of S. alterniflora introduction to the West (Pacific) coastline is disputed. Sayce (1988) suggests that S. alterniflora was introduced to Willapa Bay, WA, as a discarded packaging material for shipments of eastern oyster spats originating from the east coast of North America. Initially, the species established on the west side of Long Island (Sayce, 1988). However, Cohen and Carlton (1995) have suggested that the earliest report of S. alterniflora occurred around 1911, suggesting that solid ballast material is the most likely transport mechanism. Irrespective of the initial means of introduction, the plant was not accurately identified until 1940s, when the plants flowered (Scheffer, 1945; Sayce, 1988). The clumps, which covered several hectares at that time, had first been noted around 1911 (Scheffer, 1945). During the first 50 years, the population slowly expanded, but from 1945 to 1988 the plant became established throughout the bay, forming vast meadows (Sayce, 1988). After nearly a century of expansion the initial infestation in Willapa Bay spread to a maximum extent of 3500 hectares in 2003. Recent control methods, during 2005/6 have notably reduced the extent of the Willapa population (Murphy et al., 2007). In Puget Sound, WA, S. alterniflora was introduced to stabilize coastlines and increase the vegetative cover of mudflats to reduce wave impact. The Dike Island Gun Club planted S. alterniflora in Padilla Bay in the 1940s to stabilize an island in the south bay. S. alterniflora was also introduced to Thorndyke Bay, Kala Point, and Sequim Bay to increase vegetative cover (Ebasco Environmental, 1992).

In California, S. alterniflora is found at multiple sites in the San Francisco Bay, mostly concentrated in the southern part of the bay (Callaway and Josselyn, 1992; Cohen and Carlton, 1995). A small population was eradicated from Humbolt Bay. Also present in Bolinas Lagoon and the bays of Point Reyes National Seashore, north of San Francisco, where it is being smothered or dug out (Howard, 2008).

Non-indigenous populations of S. alterniflora are also documented in Australia, New Zealand, China, France, the Netherlands and United Kingdom.

Soil drainage

• free
• impeded

Soil reaction

• acid
• alkaline
• neutral

Soil texture

• light

Special soil tolerances

• infertile
• saline

Impact on Habitats 

Within its introduced range a concern is being raised over S. alterniflora impact to habitats where present due to its ability to reduce tidal energy and trap sediment. On the East and Gulf native coastal ranges, where S. alterniflora is a major component of salt marsh vegetation, wave energy is high, however the presence of S. alterniflora allows for sediment accretion rates of 13 mm/year, with higher stem densities resulting in higher sediment deposition rates and steeper beach profiles (Gleason et al., 1979; Simenstad and Thom, 1995). Where S. alterniflora has been introduced to San Francisco Bay, sediment accretion rates have been estimated at 1.4 to 13.3 mm/yr. (Callaway, 1990; Josselyn et al., 1993; Simenstad and Thom, 1995). In contrast, a study of low intertidal salt marshes in Washington and Oregon that lacked S. alterniflora found that the sediment accretion rate ranged from 2.3 to 6.6 mm/year, with a mean of 3.6 mm/year. (Thom, 1992). This higher rate of accretion rate associated with Spartina may change the fundamental nature of portions of Washington’s coastline. Before S. alterniflora was present, Pacific Northwest estuaries consisted of bare, gently sloping mud flats with shallow tidal channels. Fully developed Spartina marshes have steeply sloping seaward edges and deep, steep-sided tidal channels. S. alterniflora clones trap sediment, causing the clones to rise above the surrounding mudflats (Ebasco Environmental, 1992). Higher stem densities dissipate more wave action, therefore allowing a larger amount of sediment to be deposited and a steeper beach profile to form (Gleason et al., 1979).

Another impact of increased sediment accretion is the resultant change in water circulation patterns. Using a close relative of S. alterniflora as a guide, sediment accretion associated with S. anglica infestations in England, has been reported to reduce tidal flow (Hubbard, 1965). In addition, if large, dense populations of S. alterniflora are present around the mouth of an estuary, decreased flow may occur, leading to an increase in flooding likelihood, especially during sustained periods of heavy rainfall coinciding within above average tides (Ebasco Environmental, 1993).

Impact on Biodiversity

The spread of S. alterniflora can impact the native flora and fauna of the intertidal zone. Spartina may displace native plants, such as Zosteramarina (seagrass), Salicornia virginica, Triglochin maritimum, Jaumea carnosa, and Fucus distichus (Wiggins and Binney, 1987; Simenstad and Thom, 1995). Displacement of several of these plants is of particular concern. For example, seagrasses (Zostera spp.), provides important refuges and food sources for fish, crabs, waterfowl, and other marine life (Balthuis and Scott, 1993).

Other concerns include the replacement of open mudflat habitats associated with bottom-dwelling invertebrate communities by vegetative salt marsh species. Experimental evidence indicates that invertebrate populations in the sediments of S. alterniflora clones, in Willapa Bay are smaller than populations in surrounding non-vegetated intertidal mudflats (Norman and Patten, 1994). The loss of habitat for bivalves is of particular concern in Willapa Bay, WA, as it supports a US$16 million oyster industry. Waders and waterfowl will lose important foraging and refuge habitat. In Willapa National Wildlife Refuge, S. alterniflora has already displaced an estimated 16-20 percent of critical habitat for wintering and breeding aquatic birds (Foss, 1992).

• Invasive in its native range
• Proved invasive outside its native range
• Has a broad native range
• Abundant in its native range
• Highly adaptable to different environments
• Is a habitat generalist
• Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
• Pioneering in disturbed areas
• Benefits from human association (i.e. it is a human commensal)
• Long lived
• Fast growing
• Has high reproductive potential
• Has propagules that can remain viable for more than one year
• Reproduces asexually

• Damaged ecosystem services
• Ecosystem change/ habitat alteration
• Modification of hydrology
• Modification of natural benthic communities
• Modification of nutrient regime
• Modification of successional patterns
• Monoculture formation
• Negatively impacts agriculture
• Negatively impacts cultural/traditional practices
• Negatively impacts livelihoods
• Negatively impacts aquaculture/fisheries
• Negatively impacts tourism
• Reduced amenity values
• Reduced native biodiversity
• Soil accretion
• Threat to/ loss of native species
• Transportation disruption

• Competition - monopolizing resources
• Competition - shading
• Competition - smothering
• Hybridization
• Pollen swamping
• Rapid growth
• Rooting

• Highly likely to be transported internationally accidentally
• Difficult/costly to control

In its native habitat, S. alterniflora is of great value (Landin, 1991; Simenstad and Thom, 1995). The species is extremely productive, exporting approximately 1300 g/m² of detritus annually to the estuarine system (Landin, 1991). Within its native range, S. alterniflora became highly regarded as an erosion control tool, which led to it being widely introduced to other areas (Simenstad and Thom, 1995). Within its native habitat, S. alterniflora roots and shoots are a food source for waterfowl and wetland mammals, partly keeping the expansion of Spartina wetlands in check. In addition, stands of S. alterniflora can serve as a nursery area for mangroves, and estuarine fish and shellfish.

Because of their ability to trap sediment via decreasing wave energy, Spartina species have been introduced to many parts of the world for estuary reclamation and for erosion control (Partridge, 1987). Normally S. anglica has been used for this purpose, however, S. alterniflora has been planted in some areas, such as the North Island of New Zealand (Partridge, 1987).

There are also some economically beneficial uses for S. alterniflora. The species is palatable to livestock, especially deer and horses, so the plant’s continued spread may increase available pasture. S. alterniflora has also been investigated for use within the paper production industry (Ebasco Environmental, 1993).