S. alterniflora is an erect, perennial salt tolerant grass that characteristically grows in dense stands. The inflorescence is a flowering panicle made of many spikes and it is 10-40cm long with dense colourless flowers, which are closely appressed and overlapping. S. alterniflora blooms from July through November (The Invasive Spartina Project, 2003). Leaf blades which are grey-green in colour can be 20-55cm long and and be up to 5cm in width. The stems range in height from 60-250cm and are upto 2cm wide at the base (Brian Silliman., pers. comm., 2005) .

S. alterniflora is a dominant species in its native range, the salt marshes of the Atlantic and Gulf coasts of the USA. It plays an important role in sediment stabilization and serves as nursery grounds for estuarine fish and invertebrates. Marsh grasses like S. alterniflora are essential for land creation processes in areas such as the Chesapeake Bay (Taylor et al. 2001).S. alterniflora serves as a foundation species and is a critical carbon base for estuarine food-webs supplying carbon for the detrital and direct grazing food-web energy pathways (Brian Silliman., pers.comm., 2005).

S. alterniflora grows within lower elevational marsh zones in its native range. In the San Francisco Bay area where it is introduced S. alterniflora and its hybrids have been observed growing both lower and higher than the native S. foliosa. The tidal range for S. alterniflora varies throughout the world, but it has the potential to grow from the mean higher high water to approximately 1 metre from mean low lower water (The Invasive Spartina Project, 2003).

The Western Aquatic Plant Management Society (2004) states that, \"S. alterniflora is a plant of the intertidal zone, where it colonizes mud or sandflats in saline or brackish water. Found in areas of low to moderate wave energy, the species can colonize a broad range of substrates, ranging from sand and silt to loose cobble, clay, and gravel. The species can tolerate a wide range of environmental conditions, including: inundation up to 12 hours a day, pH levels from 4.5 to 8.5, and salinity from 10 to 60 ppt\".
Spartina can grow in terrestrial areas, but is excluded by competition from other plants. It can grow in the highest reached of the intertidal zone all the way down until ~ 1m from mean low water (Brian Silliman., pers. comm., 2005).

The Western Aquatic Plant Management Society (2004) reports that, \"Spartina alterniflora can spread by seed, rhizome, or vegetative fragmentation (Daehler and Strong 1994). However, the plant does not produce seed in several areas where it has been introduced. No flowers have been observed in New Zealand or in Padilla Bay, and the Willapa Bay population was not observed to flower for almost 50 years after its introduction (Partridge 1987; Kunz and Martz 1993; Riggs 1992; Scheffer 1945). Low soil temperature can delay or suppress flowering and reduce seed production in Spartina spp. The species is protogynous, meaning that female flowers mature before male flowers (Bertness and Shumway 1992). This strategy helps ensure out-crossing\".

S. alterniflora was introduced to Puget Sound, in the 1940s to stabilize shorelines and increase vegetative cover (Western Aquatic Plant Management Society, 2004).S. alterniflora was introduced into San Francisco Bay for salt marsh restoration in the 1970s (Ayres et al. 2003).S. alterniflora was deliberately introduced to New Zealand in the 1950's from the USA primarily for land reclamation purposes and alleged habitat enhancement (Champion and Clayton, 2004).S. alterniflora was apparently first introduced into Willapa Bay in 1894 in a shipment of eastern oyster spat originating from the east coast of North America. Initially, the species established on the west side of Long Island (Sayce 1988) (Western Aquatic Plant Management Society, 2004).

The Invasive Spartina Project (2003) list down the impacts of the introduced Spartina alterniflora in the San Francisco Bay Area:
S. alterniflora can invade mudflats and channels and convert this habitat to marshland. Loss of mudflat and channel habitat may seriously impact the foraging habitat for numerous residential as well as migrating shorebirds and waterfowl, including the federally and state endangered California clapper rail (see Rallus longirostris obsoletus in Status: U.S Fish and Wildlife Service). S. alterniflora is also invading high marsh habitat, degrading or eliminating pickleweed (Salicornia virginica) habitat, impacting habitat for the endangered salt marsh harvest mouse (see Reithrodontomys raviventris in IUCN Red List of Threatened Species)
S. alterniflora hybridizes with the native Spartina spp. S. alterniflora is therefore a threat to the survival of native Spartina spp. Given the robust form and reproductive vigor of both the introduced S. alterniflora and their hybrids. Hybrids have variable morphology and may be more vigorous than S. alterniflora. Hybrids are difficult to distinguish from either parent species in the field. Molecular lab tests are required to confirm S. alterniflora or hybrid identification
S. alterniflora can cause increased rates of sedimentation, leading to the eventual clogging of flood control channels and natural sloughs, raising them to the overall elevation of the marsh plain.

For details on preventative, physical, chemical and biological control of this species please read our pdf file on management information.