Plants perennial, with extensive rhizomes, forming large clumps or colonies, monoecious. Flowering stems 100–400 cm long, usually branched, erect to spreading, often rooting at the nodes, glabrous. Leaf sheaths glabrous, open for their entire length, the ligule 10–25 mm long, membranous, minutely hairy on the surface. Leaf blades 40–100 cm long, 10–30 mm wide, flat at maturity, glabrous, minutely but strongly roughened along the margins. Inflorescences open panicles with the spikelets somewhat differentiated in shape, the staminate spikelets toward the base of the inflorescence branches and the pistillate spikelets toward the tip of the same branches. Spikelets lacking glumes, disarticulating at the base, the stalks only slightly thickened at the tip. Lemmas with the body 6–9 mm long, broadly lanceolate, those of the staminate spikelets tapered to an awnless, pointed tip, those of the pistillate spikelets tapered to an awn 1–5 mm long and with the margins wrapped around the palea and developing fruit, papery, 7‑nerved, glabrous but roughened along the nerves. Paleas slightly longer than the body of the lemma, lanceolate, tapered to a pointed, awnless tip, strongly 3‑nerved, glabrous but roughened along the nerves. Staminate spikelets with 6 stamens. Fruits with the body 2.8–3.5 mm long, obovate in outline, the tip with a slender, persistent style, yellowish brown, enclosed loosely by the persistent lemma and palea. 2n=24. April–August.

Scattered in the Mississippi Lowlands Division and southeastern portion of the Ozarks (Atlantic and Gulf Coastal Plain of the southeastern U.S. and inland along the Mississippi Embayment to Kentucky and Missouri; Mexico). Swamps, sloughs, ditches, canals, margins of lakes, ponds, and sinkhole ponds, and banks of streams and rivers; emergent aquatics.

This robust perennial often forms large stands. Holmes and Stalling (1990) studied the reproductive ecology of Z. miliacea and found that in addition to fruits the plants reproduce vegetatively by producing vegetative buds at the nodes of the flowering stems. These germinate and form new plants if the stem falls over or breaks away and is carried by water to a new site.

Steyermark noted that the margins of Zizaniopsis leaves are “. . . razor‑sharp, easily cutting the flesh when handled.” Collectors should use caution when sampling this species.