Glyceria grandis (American Manna Grass)

Plant Info
Also known as: Reed Mannagrass, Tall Manna Grass
Family:Poaceae (Grass)
Life cycle:perennial
Habitat:sun; wet; shallow water, swamps, marshes, streams, ponds, lakeshores, wet ditches
Fruiting season:July - September
Plant height:3 to 5 feet
Wetland Indicator Status:GP: OBL MW: OBL NCNE: OBL
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: indistinct Cluster type: panicle

[photo of panicle] Flowering head is a semi-erect, open panicle 5 to 10 inches long and about half as wide, many branched, the branches spreading to ascending with drooping tips and 15 to 50 spikelets (flower clusters).  Spikelets are stalked, appressed, lance-oblong in outline, slightly flattened, 5 to 7 mm long; 2 to 2.5 mm wide, each with 4 to 9 fertile florets. 1 or more florets at the tip may be sterile.

[photo of spikelets] At the base of a spikelet is a pair of bracts (glumes), both lance-elliptic with pointed tips, papery thin, obscurely 1-nerved, the lower glume 1.2 to 2 mm long, the upper glume 1.5 to 2.5 mm long. Surrounding a floret is a pair of bracts (lemma and palea). The lemma is dark purplish, hairless, awnless, lance-oblong with a blunt tip, 2 to 2.7 mm long with 7 prominent nerves. The palea is about as long as the lemma, is notched at the tip and is 2-nerved. Sterile florets are similar to fertile florets but underdeveloped.

Leaves and stems: Leaf attachment: alternate Leaf type: simple

[photo of sheath, ligule and node] Leaf blades are 6 to 12 inches long, ¼ to 5/8 inch wide, surfaces hairless and quite shiny, the underside smooth, the upper surface rough to the touch, with a prominent midvein. Sheaths are tubular, loosely wrapping the stem, smooth or slightly rough, the edges fused at the front (a closed sheath) the entire length or nearly so. The ligule (membrane where the leaf joins the sheath) is thin and white translucent, 3 to 6 mm long, rounded to jagged along the top edge. The collar (outer junction between the blade and sheath) is prominent and distinctly yellow colored. Nodes are smooth.

[photo of inner sheath surface] The inner sheath surface is prominently cross-hatched between the veins (septate-nodulose). Stems are typically multiple from the base, stout, smooth, erect or prostrate but rising at the tip (decumbent) and may root at the nodes.

Fruit: Fruit type: seed without plume

[photo of mature floret and grain] Spikelets turn brown at maturity, the florets shedding from the tip, the glumes left behind persisting on the stalk. Grains are dark brown, somewhat flattened, oval to oblong, 1.2 to 1.3 mm long, .6 to .7 mm wide.


American Manna Grass is a robust, handsome species common to open shallow waters or mud throughout Minnesota. It can generally be distinguished by its shiny, succulent foliage and stem, and light yellow-green color. The spikelets and panicle most closely resemble those of Torry's Manna Grass (Torreyochloa pallida), which has open sheaths with edges that may overlap but are not fused at the front, and the upper glume is typically 3-nerved, where Glyceria species have closed sheaths and 1-nerved glumes. American Manna Grass is also similar in form to the related Fowl Manna Grass (G. striata), which has smaller spikelets (2.5 to 4 mm long), lemma (1.5 to 2 mm long) and ligules (1 to 3 mm long).

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More photos

Photos courtesy Peter M. Dziuk taken in Lake and Winona counties.


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