any of a genus (Ammophila) of deeply rooted, tough, perennial grasses that grow on sandy beaches and are often planted to combat beach erosion
See beach grass in American Heritage Dictionary 4
noun
A perennial grass of the genus Ammophila, especially A. breviligulata, native to sandy shores along the Great Lakes and Atlantic coast of North America, and having spikelets in long, erect, crowded clusters. It is commonly planted as a sand binder to stabilize dunes and combat beach erosion. Also called marram.