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| NAS - Nonindigenous Aquatic Species |
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Common Name: reed manna grass
Synonyms and Other Names: Glyceria spectabilis Mert. & Koch, Molinia maxima Hartman
Taxonomy: available through 
Identification: Glyceria maxima is a perennial, rhizomatous grass with unbranched stems that can grow grow up to 2.5 m high. Leaf sheaths have prominent midribs, visible transverse veins, and are closed to near the top. The unlobed, membranous ligules are 1.2-6 mm long, smooth and obtuse in shape. Leaf blades are flat, 30-60 cm long and 0.6-2.0 cm wide. The leaf blades are shallowly grooved, with prominent midribs. The leaf margins have short, stiff hairs that are rough to the touch.
These are bisexual plants with a panicles that can be either open (chasmogamous) or contracted and symmetrical. The inflorescence branches have short, stiff hairs similar to those on the leaf margins.
Glyceria could be confused with large specimens of Glyceria grandis (American mannagrass), but this species typically only grows up to 1.5 m, has nodding (rather than upright) inflorescences, and has shorter glumes and lemmas. It could also be mistaken for Puccinellia because of their similar spikelet structure and preference for wet habitats, but Glyceria is distinguished by its inability to tolerate highly alkaline soils, typically more flexible panicle branches, closed leaf sheaths, and single-veined upper glumes.
Native Range: Glyceria maxima is native to temperate Eurasia.
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| NAS - Nonindigenous Aquatic Species |
Translate this page with
Common Name: reed manna grass
Synonyms and Other Names: Glyceria spectabilis Mert. & Koch, Molinia maxima Hartman
Taxonomy: available through
Identification: Glyceria maxima is a perennial, rhizomatous grass with unbranched stems that can grow grow up to 2.5 m high. Leaf sheaths have prominent midribs, visible transverse veins, and are closed to near the top. The unlobed, membranous ligules are 1.2-6 mm long, smooth and obtuse in shape. Leaf blades are flat, 30-60 cm long and 0.6-2.0 cm wide. The leaf blades are shallowly grooved, with prominent midribs. The leaf margins have short, stiff hairs that are rough to the touch.
These are bisexual plants with a panicles that can be either open (chasmogamous) or contracted and symmetrical. The inflorescence branches have short, stiff hairs similar to those on the leaf margins.
Glyceria could be confused with large specimens of Glyceria grandis (American mannagrass), but this species typically only grows up to 1.5 m, has nodding (rather than upright) inflorescences, and has shorter glumes and lemmas. It could also be mistaken for Puccinellia because of their similar spikelet structure and preference for wet habitats, but Glyceria is distinguished by its inability to tolerate highly alkaline soils, typically more flexible panicle branches, closed leaf sheaths, and single-veined upper glumes.
Native Range: Glyceria maxima is native to temperate Eurasia.
Nonindigenous Occurrences:
The first North American record of Glyceria maxima came from Cootes Paradise, at the far west end of Lake Ontario, in the mid 1940's (Wei & Chow-Fraser 2006). It subsequently spread to other areas of Ontario, where it has overtaken native cattails and other species.
G. maxima was first found in the United States in the 1970's in Wisconsin's Racine and Milwaukee counties. Cultivated populations have also been documented in both Door and Wood Counties, and an un-vouchered specimen is noted from Calumet County. In the early 1990's it was found at three sites in Massachusetts' Ipswich River Wildlife Sanctuary in Essex county; these sites were subject to aggressive control measures, and only one site required re-treatment as of 2005.
New discoveries have occurred in recent years, with two new states reporting small infestations. In 2005, small population was detected in a residential pond near Monroe, Washington; control measures are planned for in 2007. In the fall of 2006, a dense circular patch was detected at Illinois Beach State Park, seemingly growing outward from a recently-replaced manhole cover. This population was treated in 2006 and monitoring will continue for a number of years (D. Nelson, pers. comm.).
Other stands occur in British Columbia, Newfoundland and Alaska. Overseas, it has been found invading Tasmania, New South Wales, Victoria, Queensland, as well as New Zealand.
Means of Introduction: Thought to have been introduced intentionally as a forage species in some cases (Barkworth et all 2000). Alternative pathways may include ornamental introductions or seeds hitchhiking with packing material, migrating waterfowl or workers and/or their equipment.
Status:
Impact of Introduction: Glyceria maxima can form large monotypic stands in wetlands, reducing plant species diversity - especially of seed-producing plants that provide food for wildlife. Aggressive growth has been demonstrated in both Ontario and its own native range. Because growth begins early in the spring, it can out compete other species. It has been demonstrated as an autogenic ecosystem engineer, capable of converting fast-flowing aerobic streams into partially anaerobic swamps. G. maxima's highly productive root-mats may facilitate its own growth and vegetative spread, and possibly that of secondary invaders as well (Clarke et al. 2004).
G. maxima has been used as a forage crop; it can, however, cause cyanide poisoning in cattle (Barkworth et al. 2000).
Remarks:
References
Anderson, J.E. and A.A. Reznicek. 1994. Glyceria maxima (Poaceae) in New England. Rhodora 96:97–101
Barkworth, M. E., K. M. Capels, and L. A. Vorobik (Eds). 2000. Manual of Grasses for North America North of Mexico. Utah State University, Logan, Utah, USA. <http://www.herbarium.usu.edu/webmanual/default.htm> (accessed March 22, 2003).
Clarke, A., P.S. Lake and D.J. O'Dowd. 2004. Ecological impacts on aquatic macroinvertebrates following upland stream invasion by a ponded pasture grass (Glyceria maxima) in southern Australia. Marine and Freshwater Research 55(7): 709-713.
Wei, A. & P. Chow-Fraser. 2006. Synergistic impact of water level fluctuation and invasion of Glyceria on Typha in a freshwater marsh of Lake Ontario. Aquatic Botany 84 (2006) 63–69.
Other Resources: Global Invasive Species Database, Invasive Plant Atlas of New England (IPANE), TNC Invasive Species Initiative - Weed Alert!
Author: VM Howard
Contributing Agencies: 
NOAA - GLERL
Revision Date: 6/15/2007 Citation for this information:
VM Howard. 2009. Glyceria maxima. USGS Nonindigenous Aquatic Species Database, Gainesville, FL.
<http://nas.er.usgs.gov/queries/FactSheet.asp?speciesID=1120> Revision Date: 6/15/2007
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