The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

Glyceria maxima
Glyceria maxima
(reed mannagrass)

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Glyceria maxima (Hartm.) Holmb.

Common name: reed mannagrass

Synonyms and Other Names: Catabrosa hydrophila, Exydra aquatica, Festuca aquatica, Glyceria altissima, Glyceria aquatica, Glyceria spectabilis, Heleochloa aquatica, Hydropoa spectabilis, Molinia maxima, Panicularia aquatica, Poa aquatica, tall mannagrass, English water grass, giant manna grass, reed manna grass, reed-meadow grass, reed sweet grass, sweet reedgrass, water-meadow grass

Taxonomy: available through www.itis.govITIS logo

Identification: Glyceria maxima is a perennial, helophytic, rhizomatous grass with unbranched stems. 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 (Campbell et al. 2010, Forest Health Staff 2006). 

These are bisexual plants with 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 (Boos et al. 2010, MIPN.org 2008).

Glyceria maxima could be confused with large specimens of native Glyceria grandis, but that species typically only grows up to 1.5 m, has nodding (rather than upright) inflorescences, and has shorter glumes and lemmas (parts of the grass spikelet) (Boos et al. 2000). It could also be mistaken for Puccinellia because of their similar spikelet structure and preference for wet habitats, but G. maxima is distinguished by its inability to tolerate highly alkaline soils, typically more flexible panicle branches, closed leaf sheaths, and single-veined upper glumes.

Size: up to 2.5m

Native Range: Glyceria maxima is native to temperate Eurasia.

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Nonindigenous Occurrences:

Table 1. States with nonindigenous occurrences, the earliest and latest observations in each state, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Glyceria maxima are found here.

StateFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
MI201620172Flint; St. Joseph
MN188820172Buffalo-Whitewater; Twin Cities
WA200520113Lake Washington; Skykomish; Snoqualmie
WI1975201914Bad-Montreal; Castle Rock; Door-Kewaunee; Fox; Lower Fox; Manitowoc-Sheboygan; Middle Rock; Milwaukee; Northwestern Lake Michigan; Pike-Root; South Fork Flambeau; Upper Fox; Upper Rock; Upper Wisconsin

Table last updated 5/26/2024

† Populations may not be currently present.

Ecology: Glyceria maxima is typically found in open wetlands such as marshes, meadows, shrub-carrs and along shorelines (Campbell et al. 2010, King County 2012). It performs better in waterlogged soils that have direct sunlight, but can be found in partially shaded areas adjacent to woodlands as well (Forest Health Staff 2006, van der Putten et al. 1997).

Glyceria maxima can expand into shallow water (~ 30 cm) and survive prolonged flooding because of its aerenchyma tissue and superficial root system (Lawniczak et al. 2010, Studer-Ehrensberger et al. 1993). The root system and rhizomes can extend 3 feet down into the soil (King County 2012). When growing near open water, reed mannagrass can form floating mats attached to the shore (King County 2012).

This species primarily reproduces vegetatively via rhizomes in North America (Campbell et al. 2010, Forest Health Staff 2006). Reed mannagrass emerges early in the year and concentrates up to 50% of its biomass in its root system (Westlake 1966). The energy stored in the roots and rhizomes enable this species to produce new shoots through the growing season (Buttery and Lambert 1965). Muskrats and beavers may aid the expansion of G. maxima. While foraging, plants may become uprooted and portions of the rhizomes may break off, float down stream, and re-establish (Forest Health Staff 2006).

Glyceria maxima also has florets that can bloom and produce viable seed (IPANE 2004). Individuals are in bloom between June and August. Once the inflorescences are mature, the panicle opens and rises above the other foliage (Campbell et al. 2010, Forest Health Staff 2006). The dark brown seeds are 1.5-2 mm in length, egg-shaped, and smooth except for a deep, slender furrow down the middle (IPANE 2004). Seeds dispersed in the fall will likely germinate the following spring; however, seeds can remain dormant and viable in the soil for several years (King County 2012).
During the winter, reed mannagrass becomes dormant. In early spring, regrowth occurs from rhizomes buds (King County 2012).

Means of Introduction: This species is thought to have been introduced intentionally as a forage species in some cases (Barkworth et al. 2000, USEPA 2008).  Alternative pathways may include ornamental introductions or seeds hitchhiking with packing material, migrating waterfowl or workers and/or their equipment.

Status: Established in the Great Lakes region.

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.  Glyceria 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).

Glyceria maxima has been used as a forage crop; it can, however, cause cyanide poisoning in cattle (Barkworth et al. 2000).

References: (click for full references)

Andersson, B. 2001. Macrophyte development and habitat characteristics in Sweden's large lakes. Ambio (Sweden) 30(8): 503—513.

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. Available http://www.herbarium.usu.edu/webmanual/default.htm Accessed 22 March 2003.

Bodelier, P.L.E., H. Duyts, C.W.P.M. Blom, H.J. Laanbroek. 1998. Interactions between nitrifying and denitrifying bacteria in gnotobiotic microcosms plants with the emergent macrophyte Glyceria maxima. FEMS Microbiology Ecology 25: 63—79. Available http://onlinelibrary.wiley.com/journal/10.1111/%28ISSN%291574-6941. Accessed 18 June 2012.

Boos, T., K. Kearns, C. LeClair, B. Panke, B. Scriver, and B. Williams (eds). 2010. A field guide to terrestrial invasive plants in Wisconsin. Wisconsin Department of Natural Resources. Madison, WI.

Braverman, M.P. 1996. Control of mannagrass (Glyceria declineata) and southern watergrass (Luziola fluitans) in water-seeded rice (Oryza sativa). Weed Technology 10(1):68—71.

Bureau of Plant Industry. 2012. Summary of Plant Protection Regulations: Wisconsin. Department of Agriculture, Trade & Consumer Protection. Madison, WI. 12 pp.

Buttery, B.R., and J.M. Lambert. 1965. Competition beternn Glyceria maxima and Phragmites communis in the region of Surlingham Broad: I. the competition mechanism. Journal of Ecology 53(1):163—181.

Campbell, S., P. Higman, B. Slaughter, and E. Schools. 2010. A Field Guide to Invasive Plants of Aquatic and Wetland Habitats for Michigan. Michigan DNRE, Michigan State University Extension, Michigan Natural Features Inventory. 90 pp.

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.

Department of Primary Industries, Parks, Water and Environment. 2012. Glyceria, Reed Sweet Grass (Glyceria maxima-Poa aquatica [Hartm.] Holmb.) Control Guide. Invasive Species. Available http://www.dpiw.tas.gov.au/inter.nsf/WebPages/RPIO-4ZV7D8?open. Accessed 20 August 2012.

Falck, M., and S. Garske. 2003. Invasive Non-native Plant Management During 2002. Administrative Report 02-12. Great Lakes Indian Fish & Wildlife Commission (GLIFWC). Odanah, WI. 68 pp.

Forest Health Staff. 2006. Reed Mannagrass: Glyceria maxima (Hartman) Holmb. Weed of the Week. U.S. Department of Agriculture Forest Service. Newtown, PA. 1 pp.

Harrington, C., M. Scholz, N. Culleton, and P.G. Lawlor. 2012. The use of integrated constructed wetlands (ICW) for the treatment of separated swine wastewaters. Hydrobiologia 692(1):111—119.

Harrington, C., and M. Scholz. 2010. Assessment of pre-digested piggery wastewater treatment operations with surface flow integrated constructed wetland systems. Bioresource Technology 101(18):6950—6960.

Hroudová, Z., and P. Zákravský. 1999. Vegetation dynamic in a fishpond littoral related to human impact. Hydrobiologia 415: 139—145.

Invasive Plant Atlas of New England (IPANE). 2004. Glyceria maxima (Reed mannagrass, Reed sweetgrass). Catalog of Species. University of Connecticut. Available http://www.invasive.org/weedcd/pdfs/ipane/Glyceriamaxima.pdf. Accessed 20 August 2012.

Kallner Bastviken, S., P.G. Eriksson, A. Ekström, and K. Tonderski. 2007. Seasonal denitrification potential in wetland sediments with organic matter from different plants species. Water, Air, and Soil Pollution 183:25—35.

King County Noxious Weed Control Program. 2012. Reed sweetgrass: Glyceria maxima. Noxious Weeds. King County Department of Natural Resources and Parks. Available http://www.kingcounty.gov/environment/animalsAndPlants/noxious-weeds/weed-identification/reed-sweetgrass.aspx. Accessed 6 August 2012.

Lawniczak, A.E., J. Zbierska, A. Choinski, and W. Szczepaniak. 2010. Response of emergent macrophytes to hydrological changes in a shallow lake, with special reference to nutrient cycling. Hydrobiologia 656:243—254.

Loeb, R., E. van Daalen, L.P.M. Lamers, and J.G.M. Roelofs. 2007. How soils characteristics and water quality influence the biogeochemical response to flooding in riverine wetlands. Biogeochemistry 85(3):289—302.

Maurer, D. 2009. Stopping New Invasive Plants in Their Tracks. New Invaders Watch Program, Outdoor Illinois. 3 pp.

Midwest Invasive Plant Network (MIPN.org). 2008. Keep a Look Out for New Aquatic Invasive Plants in the Midwest! National Park Service. 2 pp.

New York Invasive Species Council. 2010. Final report: a regulatory system for non-native species. Department of Environmental Conservation. Albany, NY. 131 pp.

PLANTS Team. 2012. Threatened & Endangered. PLANTS Database. United States Department of Agriculture (USDA) and Natural Resources Conservation Service (NRCS). Available http://plants.usda.gov/threat.html. Accessed 20 August 2012.

van der Putten, W.H., B.A.M. Peters, and M.S. van den Berg. 1997. Effects of litter on substrate conditions and growth of emergent macrophytes. New Phytologist 135:527—537.

Studer-Ehrensberger, K., C. Studer, and R.M.M. Crawford. 1993. Competition at community boundaries: mechanisms of vegetation structure in a dune-slack complex. Functional Ecology 7(2):156—168.

Sunblad, K., and K. Robertson. 1988. Harvesting reed sweetgrass (Glyceria maxima, Poaceae): effects on growth and rhizome storage of carbohydrates. Economic Botany 42(4): 495—502.

U.S. Army Corps of Engineers (USACE). 2011a. Aquatic Herbicides. 8 pp.

U.S. Army Corps of Engineers (USACE). 2011b. Manual harvest and mechanical control methods. 9 pp.

U.S. Environmental Protection Agency (USEPA). 2008. Predicting future introductions of nonindigenous species to the Great Lakes. Washington, DC. 138 pp.

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.

Westlake, D.F. 1966. The biomass and productivity of Glyceria maxima: I. seasonal changes in biomass. Journal of Ecology 54(3):745—753.

Author: Berent, L., and V.M. Howard

Revision Date: 8/22/2012

Citation Information:
Berent, L., and V.M. Howard, 2024, Glyceria maxima (Hartm.) Holmb.: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/FactSheet.aspx?SpeciesID=1120, Revision Date: 8/22/2012, Access Date: 5/26/2024

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.


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Citation information: U.S. Geological Survey. [2024]. Nonindigenous Aquatic Species Database. Gainesville, Florida. Accessed [5/26/2024].

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