What is "glyceria fluitans"

manna grass \manna grass\ n. (Bot.), Any of several tall slender grasses of the genus Glyceria. They have long loose panicles, have a sweet flavor or odor, and grow in moist places. Nerved manna grass is Glyceria nervata, and Floating manna grass is Glyceria fluitans.

Glyceria fluitans ( syns Festuca fluitans, Poa fluitans, Panicularia fluitans), known as Floating Sweet-grass and water mannagrass, is a species of perennial grass in the genus Glyceria native to Europe, the Mediterranean region and Western Asia and occurring in wet areas such as ditches, riverbanks and ponds.

It has a creeping rootstock, a thick stem which rises to one metre. The leaves are long, narrow and pale green, rough on both sides, often folded at the keel which lies on the surface of the water.