[Cal-IPC] Invasive: Ammophila arenaria (European beachgrass) is a clumping perennial grass (family Poaceae) found in coastal dune systems from Santa Barbara County north. European beachgrass grows more densely than native American dunegrass (Leymus mollis), trapping passing sand and creating steep dunes that run parallel to the shoreline. This prevents new sand from reaching interior dunes, resulting in changes to the structure and ecology of dune ecosystems. Native plants often cannot compete with dense stands of European beachgrass. Cal-IPC Rating: High (contributed by Mary Ann Machi)

[Wikipedia] Europe, North Africa coastlines native, Description, Noxious weed: Ammophila arenaria is a species of grass in the family Poaceae. It is known by the common names marram grass and European beachgrass.[2][3] It is one of two species of the genus Ammophila. It is native to the coastlines of Europe and North Africa where it grows in the sands of beach dunes. It is a perennial grass forming stiff, hardy clumps of erect stems up to 1.2 metres (3.9 ft) in height. It grows from a network of thick rhizomes which give it a sturdy anchor in its sand substrate and allow it to spread upward as sand accumulates. These rhizomes can grow laterally by 2 metres (6 ft 7 in) in six months. One clump can produce 100 new shoots annually.[4] The rhizomes tolerate submersion in sea water and can break off and float in the currents to establish the grass at new sites.[5] The leaves are up to 1 metre (3 ft 3 in) long and sharply pointed. The cylindrical inflorescence is up to 30 centimetres (12 in) long. It is adapted to habitat made up of shifting, accreting sand layers, as well as that composed of stabilised dunes. A. arenaria is one of the most problematic noxious weeds of coastal California. This sand-adapted grass was introduced to the beaches of western North America during the mid-19th century to provide stabilization to shifting sand dunes. It grew readily and it can now be found from California to British Columbia. The grass is invasive in the local ecosystems, forming dense monotypic stands that crowd out native vegetation, reduce species diversity of native arthropods, and cover vital open stretches of sand used for nesting by the threatened western snowy plover (Charadrius nivosus) (contributed by Mary Ann Machi)