Phragmites

Phragmites is a genus of four species of large perennial grasses found in wetlands throughout temperate and tropical regions of the world. The World Checklist of Selected Plant Families, maintained by Kew Garden in London, accepts the following four species: The cosmopolitan common reed has the generally accepted botanical name Phragmites australis. (Cav.) Trin. ex Steud. About 130 other synonyms have been proposed, and some have been widely used. Examples include Phragmites communis Trin., Arundo phragmites L., and Phragmites vulgaris (Lam.) Crép. (illegitimate name). Recent studies have characterised morphological distinctions between the introduced and native stands of Phragmites australis in North America. The Eurasian phenotype can be distinguished from the North American phenotype by its shorter ligules of up to 0.9 millimetres (0.04 in) as opposed to over 1.0 millimetre (0.04 in), shorter glumes of under 3.2 millimetres (0.13 in) against over 3.2 millimetres (0.13 in) (although there is some overlap in this character), and in culm characteristics. In North America, the status of Phragmites australis was a source of confusion and debate. It was commonly considered an exotic species and often invasive species, introduced from Europe. However, there is evidence of the existence of Phragmites as a native plant in North America long before European colonization of the continent. It is now known that the North American native forms of P. a. subsp. americanus are markedly less vigorous than European forms. The recent marked expansion of Phragmites in North America may be due to the more vigorous, but similar-looking European subsp. australis. Phragmites outcompetes native vegetation and lowers the local plant biodiversity. Phragmites forms dense thickets of vegetation that is unsuitable habitat for native fauna. Phragmites displaces native plants species such as wild rice, cattails, and native wetland orchids. Phragmites has a high above ground biomass that blocks light to other plants allowing areas to turn into Phragmites monoculture very quickly. Decomposing Phragmites increases the rate of marsh accretion more rapidly than would occur with native marsh vegetation. Phragmites australis subsp. australis is causing serious problems for many other North American hydrophyte wetland plants, including the native Phragmites australis subsp. americanus. Gallic acid released by Phragmites is degraded by ultraviolet light to produce mesoxalic acid, effectively hitting susceptible plants and seedlings with two harmful toxins. Phragmites is so difficult to control that one of the most effective methods of eradicating the plant is to burn it over 2-3 seasons. The roots grow so deep and strong that one burn is not enough. Ongoing research suggests that goats could be effectively used to control the species. Since 2017, over 80% of the beds of Phragmites in the Pass a Loutre Wildlife Management Area have been damaged by the invasive 'roseau cane scale', Nipponaclerda biwakoensis, threatening wildlife habitat throughout the affected regions of the WMA. While typically considered a noxious weed, in Louisiana the reed beds are considered critical to the stability of the shorelines of wetland areas and waterways of the Mississippi Delta, and the die-off of reed beds is believed to accelerate coastal erosion. Phragmites australis, common reed, commonly forms extensive stands (known as reed beds), which may be as much as 1 square kilometre (0.39 sq mi) or more in extent. Where conditions are suitable it can also spread at 5 metres (16 ft) or more per year by horizontal runners, which put down roots at regular intervals. It can grow in damp ground, in standing water up to 1 metre (3 ft 3 in) or so deep, or even as a floating mat. The erect stems grow to 2–6 metres (6 ft 7 in–19 ft 8 in) tall, with the tallest plants growing in areas with hot summers and fertile growing conditions.