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Water chestnut (Trapa natans)
Photo credit: Leslie J. Mehrhoff, University of Connecticut,

Reed Mannagrass

(Glyceria maxima)

Report this Species!

If you believe you have found this species anywhere in Pennsylvania, please report your findings to iMapInvasives by submitting an observation record.

Species at a Glance

Reed mannagrass has the biological attributes and past history in countries with similar habitats to give it extremely high potential as a wetland invader in the U.S. that would be extremely difficult to control. However, it has only been detected in a few locations in the U.S. where it was quickly removed successfully. This species is one which should raise a high alert whenever it is detected in natural areas. Rapid action seems to be a major factor in preventing the spread of reed mannagrass.

Similar Species

Reed mannagrass look-alikes include American mannagrass (Glyceria grandis), rattlesnake mannagrass (Glyceria canadensis), and reed canary grass (Phalaris arundinacea).


Considered a wetland species, reed mannagrass grows in wet areas including riverbanks, swamps, ponds, and wet pastures.


Reed mannagrass is native to Europe and temperate Asia. In 1975, it was first discovered in the United States in Racine County, Wisconsin. Its current distribution in this region includes Ontario, Quebec, Massachusetts, Connecticut, Wisconsin, and Illinois. 

Environmental Impacts

Outside its native range, this tall grass crowds out native species, often forming monospecific stands. Its ability to degrade wetland habitats causes these areas to be unsuitable for nesting and provides little nutrition for wildlife. Localized flooding is caused from the plant's ability to trap sediment and clog small waterways. If used as forage, young shoots are known to cause cyanide poisoning in cattle.

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