American Mannagrass is a tall plant reaching 2 to 5 feet in height. Stems can be erect but also recumbent with only the flowering head ascending, in which case it can root at the base.
Leaf blades are flat, up to 18 inches long and up to 1/2 inch wide.
The leaf sheath is closed for at least half its length, and sheaths on upper leaves are mostly closed. The ligule of the sheath is from 1 to 5 mm long, rounded to truncate. Both sheath and ligule are usually without hair. Ligules on the lower leaves more stiff than those on the upper leaves.
Inflorescence: The flowering heads are in an open panicle, 6 to 16 inches long (16-42 cm), branches spreading to drooping. The panicle is 5 to 8 inches wide (12 to 20 cm). Branches of the panicle are smooth but angled.
Spikelets are 3.2 to 10 mm long, flattened, oval to elliptic in side view and containing 4 to 10 florets. Glumes are whitish and have a midvein that extends to the tip, the lemma is also prominently 7 veined and purplish. There are 3 anthers, typical of the Poaceae. Note that within a panicle there can be considerable variation in the floret parts.
Varities: Two varieties are recognized. The most widespread is var. grandis, where the spikelets are 3.2 to 6.4 mm long with 4 to 8 florets. Var. komarovii is restricted to Alaska an the Yulon and has larger spikelets - 6 to 10 mm with 5 to 10 florets.
Habitat: American Mannagrass is found in the wet areas of shallow fresh water, shorelines, marshes, ditches, wet meadows, and wetlands. It grows from a rhizomatous root system.
Names: The genus name, Glyceria, is Greek for 'sweet', which is the taste of the grain, and is palatable. The species name, grandis, means 'big' or 'showy' as in the size of the panicle on this species. The common name "mannagrass" would then be a somewhat biblical reference. The author name for the plant classification, ‘S. Watson', refers to Sereno Watson (1826-1892), American Botanist, assistant to Asa Gray and later curator of the Gray Herbarium at Harvard.
Comparisons: There are two Glyceria species in the Garden - G. grandis and G. striata, Fowl Mannagrass. They are both plants of wet or moist areas. The two species can be easily confused with each other as both have spikelets that are short (less than 1 cm) and flattened. The key differences are in the details of the glumes and spikelet length. Fowl Mannagrass also has leaf sheaths closed for most of their length, flowering heads are shorter, 2.5 to 8 inches long (6-25 cm), branches straight to lax, lower branches widespread and drooping.
Above: The open panicles of a group of American Mannagrass. Drawing by Cindy Roche, ©Utah State University.
Below: In flower - note the typical 3 stamens and the angles of the panicle branches. Drawing courtesy USDA-NRCS PLANTS Database / Hitchcock, A.S. (rev. A. Chase). 1950. Manual of the grasses of the United States.
Below: The flowering panicle as it opens at the top of the stem.
Below: Spikelets of var. grandis, can have 4 to 8 florets with 2 glumes at the base. Note the veining on the lemmas in the 2nd photo.
Below: Spikelet detail. Photo ©Anna Gardner, University of Iowa.
Below: 1st and 2nd photos - Sheath and Ligule detail. The ligules are 1 to 5 mm long and the sheath is split open for up to half its length on lower leaves but more closed on uppers. 3rd photo - Blades have a wavy pattern and are up to 1/2 inch wide.
Notes: This grass is indigenous to the Garden. Eloise Butler catalogued it in her early Garden Records, noting it near the spring in June 1920. American Mannagrass is found in most counties of Minnesota and is one of four species of Glyceria usually found in the state: The four are: G. borealis, Small floating mannagrass; G. canadensis, Rattlesnake mannagrass; G. grandis var. grandis, American Mannagrass; and G. striata, Fowl Mannagrass.
American Mannagrass is a native perennial that grows in all of Canada and in all of the United States except the warm and humid SE from Texas and Oklahoma eastward. In is found in Minnesota throughout the state with about a dozen county exceptions, most of those in the SW Quadrant. There are about 35 species of Glyceria worldwide of which in North America there are 13 native and 3 introduced. All grow in wet areas and the native species are consumed by livestock, but are not abundant enough for major grazing use.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"