Setaria magna Griseb.

Giant Bristlegrass

Natural range:  U.S. to Mesoamerica

Habitat:  Mostly saline or brackish marshes or swamps, also in apparent freshwater swamps

Florida status:   Native. 

Recognition:  Huge grass, the stem potentially multiple cm in diameter.  Panicle to 50 cm.  Spikelets 2 mm long.  Upper lemma smooth (other Setarias with rugose upper lemmas).