This variable species is widespread from Central America to southeastern species, usually growing on seasonally wet sites; 2n = 30, 60, 90 (FNA 25). The coll. mapped here from PULA (KY) may be atypical in its narrow spike, dark shiny seeds, and rather short basal hairs in the spikelets. This coll. has been named E. contortus Ell. (S. brevibarbe var. c.), but giganteus remains the better identification. E. giganteus is often confused with alopecurioides but differs as follows (FNA 25, W): Lemma awn nearly terete (versus flattened), straight or slightly flexuous (versus spirally twisted at base); callus hairs (7-) 15-20 (-25) mm long (versus 9-14 mm), tawny or brown (versus silvery or tinged with purple); leaves usually pilose on the upper surface at maturity (versus usually glabrous).