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Ammophila (synonymous with Psamma P. Beauv.) is a genus of consisting of two or three very similar species of Poaceae. The genus name Ammophila originates from the Greek words ἄμμος ( ámmos), meaning "sand", and φίλος ( philos), meaning "friend". The for the grasses include marram grass, bent grass, and beachgrass. The grasses are found almost exclusively on the first line of dunes. Their extensive system of creeping underground stems or allows them to thrive under conditions of shifting sands and high winds, and helps stabilize the dunes and prevent coastal erosion.
Ammophila species are native to the coasts of the Atlantic Ocean where they are usually the dominant species on dunes. Their native range includes few inland regions, with the Great Lakes of North America being the main exception.
The Ammophila grasses are widely known as examples of , plants that can withstand dry conditions. Despite their occurrence on seacoasts, Ammophila grasses are not particularly tolerant of saline soils, although they can tolerate a salinity of about 15 g/L (1.5%), which makes them "moderate ".
Ammophila builds coastal dunes and thus stabilizes the sand. For that reason, the plants are seen as a useful means of reinforcing dunes around the world and have been introduced far from their native range. Alfred Wiedemann writes that Ammophila arenaria, the European species, "has been introduced into virtually every British colonial settlement within its latitudinal tolerance range, including south-east and south-west Australia, New Zealand, South Africa, the Falkland Islands, and Norfolk Island, and has been reported from Argentina and Chile." Ammophila species were introduced in the late 19th century on the Pacific coast of North America as well, and massive, intentional plantings were continued at least through 1960.
In virtually all of the locations where it has been introduced, Ammophila is now listed as invasive species. Ammophila infestations adversely affect coastal groundbirds and endemic dune plants, such as the western snowy plover, horned lark, and pink sand verbena ( Abronia umbellata subsp. breviflora). In California, efforts to cull invasive Ammophila arenaria from Morro Strand State Beach began in 2000 and involved a combination of herbicide treatments and handpulling by a California Conservation Corps crew. That initiative produced a 60 percent mortality among the Ammophila after several months, but it was estimated that several additional rounds of treatment would be needed to fully remove the infestation, and the effort specifically focused on "relatively new infestations." Bulldozing has also been used as an effective mechanical treatment for Ammophila infestations in the Pacific Northwest, but research indicates that the intensity and frequency of bulldozing employed to remove Ammophila may also harm endemic dune plants and have negative impacts on dune geomorphology.
Women from the village of Newborough, Anglesey, Wales, once used marram grass in the manufacture of mats, covers and brushes for .
Marram grass has been used for thatch in many areas close to the sea in the British Isles. The harvesting of marram grass for thatch was so widespread during the 17th century that it had the effect of destabilizing dunes, resulting in the burial of many villages, estates and farms. In 1695, the practice was banned by an Act of the Scottish Parliament:
Marram grass has a rolled leaf that creates a localized environment of water vapour concentration within the leaf and helps to prevent water loss. The stomata sit in small pits within the curls of the structure, which makes them less likely to open and lose water. The folded leaves have hairs on the inside to slow or stop air movement, much like many other xerophytes. Although they are typically found on the outside of the plant, in marram grass they are also within the leaf as this has now become a structure with more volume. The slowing of air movement also reduces the amount of water vapour being lost. A waxy plant cuticle on the leaf surface inhibits evaporation as well.
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