Spartina / patens, common name Salt Hay is the prominent grass that grows one to two feet high in the marsh lands up and down United States east coast. Roots have special cells that prevent salt from entering the plant, thus preventing loss of it's fresh water. They grow in tidal areas where the water is brackish.
The hollow stems are a beautiful green during growing season, They produce wheat like fruits and deep purple flowers from June to October. In Winter they turn brown.
In colonial days Salt Hay was used as food and bedding for their animals. Many towns and hamlets thus sprung up near marsh lands.
The marsh and it's grasses provide a habitat for young and mature crustaceans, mollusks and birds. Also for small animals, insects and migrating water fowl.
Smooth Cordgrass, (Spartina alterniflora) grows 3 to 6 feet along with the Salt Hay. It usually grows near the waters edge, which is called the low marsh. Where as the smaller Salt Hay out competes it in the high marsh.
The dead and decaying Smooth Cordgrass builds up the level of the marsh and extends it further into the open water, thus growing the marsh.
I will talk about the Common Reed grass or Phragmites / australis an invasive species crowding out the low growing Salt Hay, in a future post .
all photos taken by me ... 
sources ... wikipedia
datanuggets.org