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Glyceria maxima is an invasive wetland plant. The stems are tall, up to 2 meters or more, and the leaves are up to 15 or 20 mm wide. For those with a little familiarity with grasses it is clearly a Glyceria and might be mistaken for G. grandis, since G. maxima is not yet included in many of our regional floras. The following characters will help separate G. maxima from G. grandis.
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Glyceria grandis |
Glyceria maxima |
| spikelet length mm |
4.0 - 5.0 |
5.0 - 12.0 |
lower glume length mm |
1.6 - 1.7 |
2.0 - 3.0 |
| upper glume length mm |
2.4 - 2.5 |
3.0 - 4.0 |
| lemma length mm |
2.4 - 2.5 |
3.0 - 4.0 |
Glyceria maxima was first reported in the USA in 1975, from Racine Wisconsin. It is now known from the adjacent counties of Milwaukee and Waukesha and tentatively also from neighboring Jefferson County. It has also been reported from Wood, and Door Counties and a map dot is shown for Calumet County on the UW Stevens Point herbarium web site.
The color difference between G. maxima and G. grandis in the photo above is not diagnostic and reflects different developmental stages of the respective species.
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