Glyceria maxima

From Bugwoodwiki

Authors: Tunyalee Martin, Global Invasive Species Team, The Nature Conservancy

G. maxima
Scientific Name
Glyceria maxima
(Hartman) Holmb.
Common Names
rough mannagrass


Glyceria maxima is a perennial, semi-aquatic, rhizomatous grass. Stems are unbranched and can reach 2-8.2 ft. (0.6-2.5 m) in height.
Leaves are 12-23.6 in. (30-60 cm) long, 0.2-0.8 in. (6-20 mm) wide, with an acute apex and a prominent midrib. The leaf margins have stiff, short hairs. The leaf sheaths are rough in texture with a reddish-brown band at the leaf junction.
Flowering occurs from June through August, when flowers appear in 6-12 in. (15-30 cm) long open panicles. The panicle branches have short, stiff hairs like those on the leaf margins.
The small seeds are 0.06-0.08 in. (1.5-2 mm) long, obovoid in shape and smooth in texture. This plant reproduces primarily vegetatively through rhizomes.
Ecological Threat
Glyceria maxima occurs in sunny to semi-shady wetlands, where it can form dense impenetrable monocultures that crowd out native species. It is native to northern Eurasia and was first found in North America in 1940 on the edge of Lake Ontario.

Natural history


Glyceria maxima (Poaceae, grass family) is a perennial, rhizomatous grass. The stems are unbranched and can grow up to 0.8-2 m (rarely to 2.5 m) high, with the flowering spikes held well above the foliage. Leaf sheaths have prominent midribs, visible transverse veins, and are closed to near the top. The unlobed, membranous ligules are 5-7 mm long, smooth and obtuse in shape. Leaf blades are flat, 22-60 cm long and 0.7-2 cm wide. The leaf blades are shallowly grooved, with prominent midribs. The leaf margins have short, stiff hairs that are rough to the touch. The plants are bisexual. The inflorescence is a much-branched panicle 10-40 cm long, which can be open (chasmogamous) or contracted and symmetrical. The inflorescence branches have short, stiff hairs similar to those on the leaf margins.[1][2][3]



Glyceria maxima is native to temperate Europe and Asia, from the British Isles to Japan and Kamchatka.[4]

As a non-native, its range is large. In the USA, Glyceria maxima has been documented twice in Wisconsin and once in Massachusetts. The majority of the New World collections occur in Ontario, Canada. Other stands occur in British Columbia, Newfoundland, and Alaska.[5] Overseas, it has been found invading Tasmania, New South Wales, Victoria, Queensland, as well as New Zealand.

Stewardship summary

Glyceria maxima was first found in the USA in Wisconsin (Racine County) in 1975, and again 19 kilometers away four years later.[4] The next detection was in 1990, in Massachusetts (Essex County). Glyceria maxima reproduces vegetatively, and has the potential to be a serious invader of wetlands. Quick control action has prevented its spread in the Ipswich River Wildlife Sanctuary in Massachusetts. Active monitoring and rapid control action could prevent its spread into other susceptible areas.[4][6]

Glyceria maxima has the ability to form huge stands in wetlands. It is an agressive plant that has been invasive in Ontario for over 50 years. Even in its native range, conservationists are concerned with the ability of reed sweet-grass to form monocultures under different levels of disturbance. Reed sweet-grass has a competitive advantage because growth starts early in the spring. Glyceria maxima reduces plant species diversity[4], in particular, seed producing plants that provide food for wildlife. Glyceria maxima is a poor food-plant and nesting substrate for wetland wildlife.[4] Glyceria maxima has been used as a forage crop. However, several instances of cattle poisoning have occurred due to cyanide production in the young shoots.[7]


Little is known on the control of this new invader.

  1. If removing G. maxima by hand, concentrate on removing all pieces of the root or resprouting may occur.
  2. Black plastic used to smother the grass was 100% effective in Massachusetts. However, this method is not feasible over large areas.[6]
  3. A 3% solution of glyphosate (Rodeo) during early summer and late summer months has been effective. Follow-up treatments the year after application is recommended.[6]
  4. Cutting may reduce populations of reed sweet-grass by allowing sunlight to reach other, competitive plants. Multiple cuttings (more than three) may reduce the amount of carbohydrates stored in the rhizomes. Cutting during the fall months when carbohydrates and nutrients are stored for the winter may affect spring regrowth.[8]
  5. Flooding cut stubble may drown G. maxima.[7]
  6. Since several instances of cattle poisoning have occurred due to cyanide production in the young shoots, grazing is not recommended.[7]


Information sources


  1. Tutin, T.G., Heywood, V.H., Burges, N.A., & Valentine, D.H. 1980. Flora Europaea vol. 5. Cambridge University Press.
  2. Stace, C.A. 1997. New Flora of the British Isles, ed. 2. Cambridge University Press.
  3. Anonymous 2000a. broken link
  4. Anderson, J.E. and Reznicek, A.A. 1994. Glyceria maxima (Poaceae) in New England. Rhodora 96(885):97-101. 4.0 4.1 4.2 4.3 4.4
  5. Anonymous 2000b. Alaska Botanical Biodiversity: Fort Wainwright vascular plant species
  6. Rawinski, T.J. (undated) Prevention Strategies in Wetlands. Massachusetts Audubon Society in house memo. 6.0 6.1 6.2
  7. Sundblad, K. and Wittgren, H.B. 1989. Glyceria maxima for Wastewater Nutrient Removal and Forage Production. Biological Wastes 27(1):29-42., 7.0 7.1 7.2
  8. Sundblad, K. and Robertson, K. 1988. Harvesting Reed Sweetgrass (Glyceria maxima, Poaceae): Effects of Growth and Rhizome Storage of Carbohydrates. Hydrobiology 340:259-263

Additional References

Source document

Weed Alert: Glyceria maxima; Tunyalee Martin, 2000.

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