Glyceria is a cosmopolitan genus found in wet areas such as shallow, fresh water. All species within this genus are palatable, but many are found in marshes and wetlands, which are quickly degraded by grazing. Small floating mannagrass is a native species, widespread across northern North America, where it is typically found in marshes and around freshwater streams and lakes, and may grow in water up to 2 feet deep. In Iowa, populations of this species are located almost exclusively in the northwestern portion of the state, in the lake district, but one population is known from Pilot Knob State Park in Linn County. Small floating mannagrass flowers from June into August in Iowa. Four species of Glyceria occur in Iowa, and this one is most similar to eastern mannagrass (Glyceria septentrionalis) as both have relatively long spikelets (1-2 cm) that are more or less rounded in cross-section. A careful look at the lemmas of the spikelets using a hand lens will show that small floating mannagrass has lemmas that are smooth between the veins, and the first glumes are about 1-2 mm long. In contrast, eastern mannagrass has lemmas that are minutely roughened between the veins, and the first glumes are usually about 2-4 mm long (sometimes about 1 mm long). The two species overlap in distribution only 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, borealis = north or northern, referring to the northerly distribution of this species.

Plants perennial, rhizomatous. Culms 60-100 cm, the bases reclining on the ground, but becoming erect above. Leaves with the sheaths closed for most of their length, glabrous, smooth; ligules 4-12 mm long; blades 12-30 (-34) cm long, 3-6 mm wide, smooth to slightly rough above. Flowering heads 20-40 cm long, the base often included in the upper leaf sheath at maturity; branches 5-10 (-15) cm, usually erect, occasionally spreading. Spikelets 10-16 mm long, with (7-) 8-10 florets, stalks very short to as long as the spikelet. First glumes 1.5-2 mm long; second glumes 2.5-3.3 mm long, rounded; lemmas 3.3-3.8 mm long, glabrous between the veins, the apex rounded to obtuse; paleas equaling or exceeding the lemma by 0.5 mm; anthers 3. Chromosome number 2n = 20.