eastern mannagrass (floating mannagrass)
Glyceria septentrionalis Hitchc.

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habithabitpanicle sectionspikeletsfloretsfloret detailillustration

Glyceria is a cosmopolitan genus found in wet areas such as shallow, fresh water. All the species within the genus are palatable, but the typical habitats for many species are wetlands and marshes that are quickly degraded by grazing. Eastern mannagrass is a widespread native species is typically found in shallow water and wet ground. This species is found in central and southeastern counties in the state of Iowa, and flowers from June into September. Of the four Iowa species of mannagrass, this one most resembles small floating mannagrass (Glyceria borealis). You’ll need a hand lens to do this, but the two are distinguished by the presence of minute roughening between the veins of the lemmas and first glumes usually about 2-4 mm long (but sometimes as short as 1 mm) in eastern mannagrass. Small floating mannagrass has lemmas that are smooth between the veins and first glumes 1-2 mm long. Of course, eastern mannagrass is not found in northwestern Iowa, but both species occur in Linn County. Spikelets in this genus tend to shatter relatively quickly once the grains are ripe, so it is often difficult to find complete spikelets later in the growing season.

Etymology: Glyceria from the Greek glukeros = sweet, referring to the sweet seed of the type species; from the Latin, septentrionalis = north or northern, referring to the relatively northerly distribution of this species (although it is more southern than G. borealis).


Plants perennial, rhizomatous. Culms (75-) 100-140 cm, the bases reclining on the ground but with the tip ascending, rooting from the lower nodes. Leaves with the sheaths closed for 9/10 of their length, smooth or slightly roughened; ligules 4-9 mm long; blades 10-25 cm long, 4-9 mm wide, smooth below, slightly roughened above, gradually tapering to a narrow tip. Flowering heads 20-46 cm long; branches to 10 cm, often spreading at pollination. Spikelets 13-18 mm long, with 8-16 florets, stalks very short to as long as the spikelet. Glumes elliptic to obovate; first glumes 2-3 mm long; second glumes 3-4 mm long; lemmas 4-4.5 mm long, minutely roughened, the apex blunt, with the margin irregularly toothed; paleas usually slightly shorter than the lemma; anthers 3. Chromosome number 2n = 40.



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