G. aquatica: aquatic; stems stout, reed-like, 4-6 feet high; leaves flat, very rough on the edges; panicle much branched, spreading, nearly a foot long, the spikelets numerous. - Wet ditches and shallow waters. Fl. July.
G. fluitans: aquatic; stems 2-3 feet high, rather weak, creeping at the base; leaves often floating; panicle erect and slender, a foot long, the branches few, usually erect; spikelets 1/2-1 inch long. - Flote-grass. - Wet ditches and stagnant waters. Fl. June to September.