Hordeum marinum, commonly known as sea barley or (subspecies gussoneanum) Mediterranean barley, is a species of flowering plant in the grass family Poaceae that grows on bare ground on the shores of Europe and North Africa. It is also found in inland salt flats such as the Pannonian grasslands of Hungary, and it is widely established outside its range in temperate regions of both the north and south hemispheres. It is an annual, producing copious seed when habitat conditions are right, but not persisting in competition with other species. Although it is a relative of an important crop species, it has no uses itself.

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