Glyceria canadensis (Rattlesnake Manna Grass)

Plant Info
Also known as:
Family:Poaceae (Grass)
Life cycle:perennial
Habitat:part shade, sun; wet; swamps, bogs, shores, wet woods
Fruiting season:July - October
Plant height:2 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 diffuse, open panicle 5 to 10 inches long, often nodding to one side, the branches spreading to ascending but typically drooping, the lower branches each with 3 to 12 spikelets (flower clusters). Spikelets are solitary at branchlet tips, lance-oval in outline, flattened on one-plane, 1/8 to 1/3 inch (3 to 8 mm) long, about 1/8 inch wide, each with 5 to 10 florets and a stalk that is often much longer than the spikelet. 1 or more florets at the tip may be sterile.

[photo of spikelet] At the base of a spikelet is a pair of bracts (glumes), both with pointed tips, obscure veins and thin, papery edging. The lower glume is lance-oblong, 1.5 to 2.5 mm long, the upper glume is more broadly lance-oval, 2 to 3 mm long. Surrounding a floret is a pair of bracts (lemma and palea), the lemma lance to egg-shaped, pointed at the tip but awnless, hairless but rough along the veins, 3 to 4 mm long with 7 obscure veins and papery thin edging. The palea is somewhat broader and shorter than the lemma, rounded and narrowly notched at the tip. Sterile florets are similar to fertile florets, but underdeveloped.

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

[photo of leaves] Leaf blades are 6 to 12 inches long, ¼ to 1/3 inch wide with a prominent midvein, the surfaces hairless but may be slightly rough to the touch.

[photo of sheath, ligule and node] Sheaths are slightly keeled at the back, the edges fused at the front for most of their length (a closed sheath) except at the tip where it forms an open "V", surfaces hairless but slightly rough textured. Sheaths are shorter than the internodes and not overlapping except near the base of the stem. The ligule (membrane where the leaf joins the sheath) is thin, 1 to 3 mm long, jagged and torn across the top. Nodes are smooth. Stems one to several in a loose clump, mostly smooth or slightly rough between the nodes. 

Fruit: Fruit type: seed without plume

[photo of mature spikelets] Spikelets turn light brown at maturity, the florets shedding from the tip, the glumes left behind and persisting on the stalk.

[photo of mature florets and grain] Grains are brown, somewhat flattened, oval, 1.3 to 1.5 mm long.


While Rattlesnake Manna Grass is apparently tightly restricted to wetland habitats in east central and northeasten counties in Minnesota, it is both frequent and often abundant within that range. Its large, showy cascading heads and large spikelets are distinctive and readily stand out among other vegetation. There are 2 varieties, though they are apparently not universally accepted: var. laxa (a.k.a Glyceria laxa) is an east coast species with smaller florets and only up to 5 per spikelet; var. canadensis is found from Minnesota to New England and into Canada, and described above.

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More photos

Photos by K. Chayka taken in Pine County. Photos courtesy Peter M. Dziuk taken in Cook, Isanti and Lake counties.


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