Reed mannagrass

Scientific Name: Glyceria maxima

Leslie J. Mehrhoff, University of Connecticut, Bugwood.orgCopyright Info

Identification: Reed mannagrass is a perennial plant with narrow leaves that arise from a horizontal stem. The leaves have shallow grooves, a prominent center vein, and short, stiff hairs on the edges that are rough to the touch. The flowering stem is branched and carries many narrow spike-shaped flowers that develop into small oval seeds. This species is also called reed sweetgrass.

Size: This species can grow up to 8 feet (2.5 m) tall. Its leaves are 1-2 feet (30-60 cm) long and 0.25-0.75 inch (0.6-2 cm) wide.

Native Range: Reed mannagrass is native to Eurasia.

Table 1. Great Lakes region nonindigenous occurrences, the earliest and latest observations in each state/province, 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.

Full list of USGS occurrences

State/ProvinceYear of earliest observationYear of last observationTotal HUCs with observations†HUCs with observations†
Michigan201620172Flint; St. Joseph
Wisconsin197920177Bad-Montreal; Door-Kewaunee; Fox; Manitowoc-Sheboygan; Milwaukee; Northwestern Lake Michigan; Pike-Root

Table last updated 9/30/2019

† Populations may not be currently present.

Means of Introduction: This species may have been introduced intentionally as a food source for livestock and has been planted as an ornamental grass. It may spread unintentionally through seeds that attach to a variety of materials, including packing material, equipment, workers, or migrating waterfowl. Once introduced, it grows and spreads aggressively by seed dispersal and by horizontal stem growth.

Status: Reed mannagrass was first recorded in North America on the Canadian shore of Lake Ontario in the mid 1940s. It subsequently spread to other areas of Ontario, where it has overtaken native cattails and other species. It was first found in the United States in the 1970s in southern Wisconsin’s Racine and Milwaukee counties. Populations have been documented elsewhere in Wisconsin and in Massachusetts, Illinois, Washington, and Alaska. It has also been found in British Columbia and Newfoundland in Canada.

Remarks: While reed mannagrass has been used as a food source for livestock, young plants contain cyanide at levels high enough to poison cattle.

Author: Illinois-Indiana Sea Grant

Contributing Agencies:
NOAA Sea Grant GLRI Logo

Revision Date: 8/31/2012

Citation for this information:
Illinois-Indiana Sea Grant, 2019, Reed mannagrass: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI,, Revision Date: 8/31/2012, Access Date: 12/8/2019

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.