Large-headed rush first might be encountered as a stand growing along a wet ditch, or in open water. It can be confused with other large-headed Juncus species, of which there are 21 in Florida (Wunderlin, 2003). In the US, large-headed rush occurs in the south and extends west to TX (Kartesz, 1999).
Large-headed rush is a true rush. Stems clump-forming, to 3 ft. tall; leaf blades rounded with cross partitions, no longer than sheath or absent; sheaths purplish, loose; inflorescence spherical heads, to 1/4 in. across; bract inconspicuous; flowers stiff, purplish, flower segments lance-shaped with sharp tips; capsule narrow, pointed, not longer than flower.