Beach Grass Definition

noun
Either of two perennial rhizomatous grasses, Ammophila breviligulata of the Great Lakes and Atlantic coast of North America, or A. arenaria of Europe and North Africa and naturalized elsewhere, having spikelets in long, erect, dense clusters and growing on sandy dunes.
American Heritage
Any of a genus (Ammophila) of deeply rooted, tough, perennial grasses that grow on sandy beaches and are often planted to combat beach erosion.
Webster's New World