American mannagrass
Glyceria grandis S. Watson

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Glyceria is a cosmopolitan genus found in wet areas such as shallow, fresh water. All species within the genus are palatable, but the typical habitats for many are marshes and wetlands that are quickly degraded by grazing. American mannagrass is found throughout the northern 2/3 of the state of Iowa, primarily on marshy ground and in shallow water. It flowers from late June into August. Of the four species of Glyceria in Iowa, this one is most easily confused with fowl mannagrass (Glyceria striata), as both have relatively short spikelets (less than 1 cm) that are flattened. American mannagrass has first glumes 1.2-2 mm long and three stamens per flower, whereas fowl mannagrass has first glumes 0.5-1 mm long and two stamens per flower. Many species in this genus, including this one, are planted in and around aquatic gardens because they have open attractive panicles. 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 grandis = large, great, big, tall, lofty, referring to the relatively large size of the plants.


Plants perennial, rhizomatous. Culms 70-150 cm, erect or the bases reclining on the ground but with the tip ascending. Leaves with the sheaths closed for at least half their length, the upper sheaths closed to near the tops, all sheaths glabrous and smooth to minutely roughened; ligules 2-6 mm long, truncate or rounded, those of the lower leaves stiff at the base, those of the upper ones flexible throughout; blades 22-44 cm long, 5-13 mm wide. Flowering heads 25-37 cm long, open; branches spreading to drooping. Spikelets (3.9-) 4.5-6.6 mm long, 1.5-2.3 mm wide, with (3-) 4-7 florets. Glumes acute, the midvein extending to the tip; first glume 1.2-2 mm long; second glume 1.7-2.3 mm long; lemma 1.8-2.5 mm long, prominently (5-) 7-veined, the veins often slightly roughened, the area between the veins smooth, the tip flat at maturity; palea equaling to slightly longer than the lemma; anthers 3. Chromosome number 2n = 20.



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