Smooth cordgrass

Spartina alterniflora, the smooth cordgrass, saltmarsh cordgrass, or salt-water cordgrass, is a perennial deciduous grass which is found in intertidal wetlands, especially estuarine salt marshes. It grows 1–1.5 m tall and has smooth, hollow stems which bear leaves up to 20–60 cm long and 1.5 cm wide at their base, which are sharply tapered and bend down at their tips. Like its relative saltmeadow cordgrass ''S. patens'', it produces flowers and seeds on only one side of the stalk. The flowers are a yellowish-green, turning brown by the winter. It has rhizoidal roots, which, when broken off, can result in vegetative asexual growth. The roots are an important food resource for snow geese. It can grow in low marsh as well as high marsh , but it is usually restricted to low marsh because it is outcompeted by salt meadow cordgrass in the high marsh. It grows in a wide range of salinities, from about 5 psu to marine , and has been described as the "single most important marsh plant species in the estuary" of Chesapeake Bay. It is described as intolerant of shade.

''S. alterniflora'' is noted for its capacity to act as an environmental engineer. It grows out into the water at the seaward edge of a salt marsh, and accumulates sediment and enables other habitat-engineering species, such as mussels, to settle. This accumulation of sediment and other substrate-building species gradually builds up the level of the land at the seaward edge, and other, higher-marsh species move onto the new land. As the marsh accretes, ''S. alterniflora'' moves still further out to form a new edge. ''S. alterniflora'' grows in tallest forms at the outermost edge of a given marsh, displaying shorter morphologies up onto the landward side of the ''Spartina'' belt.

''S. alterniflora'' is native to the Atlantic coast of the Americas from Newfoundland, Canada, south to northern Argentina, where it forms a dominant part of brackish coastal saltmarshes.