Glyceria borealis (Northern Manna Grass)
|Also known as:||Small Floating Mannagrass|
|Habitat:||sun; wet; shallow water, streams, ponds, lakeshores, wet ditches|
|Fruiting season:||July - September|
|Plant height:||2 to 5 feet|
|Wetland Indicator Status:||GP: OBL MW: OBL NCNE: OBL|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Flowering cluster is weakly erect and narrow, excerting out of the upper most leaf sheath, 8 to 20 inches long, the sparse panicle branches 3 to 4½ inches long each with 5 to 12 alternately attached, appressed spikelets (flower clusters). Spikelets are 3/8 to ¾ inch (1-2 cm) long, somewhat flattened with 6 to 12 florets, on a stalk ¼ to about ½ as long as the spikelet. 1 or more florets at the tip may be sterile.
At the base of a spikelet is a pair of bracts (glumes), elliptic with obscure veins, the lower glume 1.1 to 2.1 mm long, the upper glume 1.9 to 3.3 mm long, the rounded tips becoming papery. Surrounding a floret are a pair of bracts (lemma and palea), the lemma narrowly egg-shaped, broadest below the middle, 3.1 to 3.9 mm long, 7-nerved, blunt at the tip, hairless but rough along the veins, awnless, purplish, irregularily notched, with papery, translucent white edging. The palea is 2-nerved and about as long as the lemma. Sterile florets are similar to fertile florets, but underdeveloped.
Leaves and stems:
Plants are typically in shallow water, early leaves floating in rafts on the surface, the blades linear, 6 to 20 inches long, 1/8 to ¼ inch wide, abruptly tapered to a point, folded or flat with a prominent midvein. Surfaces are dark blueish green and hairless, the upper surface covered in pimply projections (papillose). Emergent leaves are erect but weak and collapsing with age.
The sheath is somewhat flattened, 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 are smooth to slightly rough and green to deep red, the submerged sheaths red. The ligule (membrane where the leaf joins the sheath) is a loose, thin, membranous band ¼ to ½ inch long, tapering to ragged point at the tip but often folded over. Nodes are hairless and green. Stems are hairless, the lower stem often prostrate along ground/lake bottom before rising (decumbent), and rooting at the nodes.
Spikelets turn brown at maturity, the florets quickly shedding as each grain matures, the glumes left behind and persisting on the stalk. Grains are a greenish brown, oval, 1 mm long, .5 to .75 mm wide.
Northern Manna Grass is fairly common in shallow water bodies and shorelines throughout Minnesota's east central deciduous and northeastern coniferous forest regions. While its floating leaves can be observed long before the flowering panicle appears, these could be confused with some of the Bur-reeds (Sparganium ssp.) but Northern Manna Grass can be distinguished by sheaths with fused edges, its reddish-purple to blueish-green floating leaves with a prominent midvein and by its deep red, submerged sheaths.
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- Northern Manna Grass plants
- Northern Manna Grass plants
- emergent leaves with red sheaths
- a loose colony of Northern Manna Grass floating leaves
- papillose upper leaf surface
Photos courtesy Peter M. Dziuk taken in Aitkin, Lake, Pine and Wright counties.
Have you seen this plant in Minnesota, or have any other comments about it?