This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol1", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Culms 2°-5° long, flattened, erect or decumbent, usually stout, simple, smooth and glabrous, often rooting from the lower nodes. Sheaths loose, generally overlapping, smooth or rough; ligule 2"-3" long; blades 5'-1° long or more, 2"-6" wide, scabrous, often floating; panicle 9'-1 1/2º long, the branches, at least the lower ones, at first appressed, later ascending, and 3'-6' long; spikelets linear, 7-13-flowered, 4"-12" long; empty scales unequal, 1-nerved, the lower acute or obtuse, the upper obtuse or truncate; flowering scales 1 1/2"-2 1/4" long, oblong, rounded or truncate at the erose apex, more or less scabrous, sharply 7-nerved.
Soc. Nat. Hist. 2: 91. 1895. Not G. angustata T.
Glabrous. Culms erect from a creeping base, 1 1/2°-5°tall; sheaths overlapping, smooth or rough-ish, the uppermost one enclosing the base of the panicle; ligule 2 1/2"-7 1/2" long, membranous; blades linear, abruptly acuminate, 3 1/2'-21' long, 1"-5" wide; panicle slender, narrow, the exserted portion 6'-2o' long, its branches appressed or nearly so, the lower in 2's of 3's, the longer of which bear 5-12 spikelets; spikelets 5"-9" long, 7-13-flowered, appressed; outer two scales empty, i-nerved, smooth and shining, unequal; flowering scales thin, 2"-2 1/2" long, 7-nerved, the nerves hispidulous, a broad scarious margin at the obtuse and erose apex; palet hyaline, shortly 2-toothed at the obtuse apex.
In shallow water, Newfoundland to Alaska, south to New York, Minnesota, Iowa and Oregon, and in the mountains to Colorado. June-Aug.
Festuca fluitans L. Sp. PI. 75. 1753.
Glyceria fluitans R. Br. Prod. 1: 179. 1810.
P. fluitans Kuntze, Rev. Gen. 782. 1891.
P. brachyphylla Nash, Bull. Torr. Club 24: 349. 1897.
Culms erect from a creeping base, 2°-3° tall; sheaths generally longer than the internodes, almost closed, the uppermost one enclosing the base of the panicle; blades linear, acuminate, 2 1/2'-5' long, 2"-2i" wide; panicle slender, its branches appressed or nearly so, the lower in 2's or 3's, the longer of which bear 2 or 3 spikelets; spikelets compressed-cylindric, 10"-14" long, 7-12-flowered; flowering scales hispidulous all over, 7-nerved, about 2i" long, the obtuse apex obscurely and irregularly few-toothed; palet acuminate, a little exceeding the scale.
In shallow water, Gulf of St. Lawrence and near New York City. Perhaps introduced. Common in Europe. Flote-grass, Russia-grass, Manna Croup-grass, Poland Manna. June-July.