Plants annual or perennial; cespitose from a hard, knotty base. Culms 30-200 cm, erect, branching; nodes glabrous. Sheaths glabrous, margins ciliate; ligules 1.5-2.7 mm; blades 15-55 cm long, 4-18 mm wide, flat, glabrous or pubescent. Panicles terminal, 10-25 cm long, 15-30 mm wide, fully exerted from the sheaths, erect to drooping, white, yellow, light brown, or pink to deep purple; rachises terete, scabrous. Fascicles 33-45 per cm, disarticulating at maturity; fascicles axes 0.2-0.5 mm, with 1 spikelet; outer bristles 13-30, 1.3-5 mm, scabrous; inner bristles 6-14, 4.3-11.5 mm, long ciliate; primary bristles 14-25 mm, long-ciliate, noticeably longer than the other bristles. Spikelets 3-4.5 mm, sessile; lower glumes absent or to 2 mm, veinless; upper glumes 3-4.5 mm, glabrous, 5-7-veined, 3-lobed; lower florets sterile or staminate; lower lemmas 3-3.9 mm, 5-7-veined, apices lobed; lower paleas 2.9-3.7 mm; anthers absent or 1.7-2 mm; upper florets disarticulating at maturity; upper lemmas 1.7-3 mm, coriaceous, shiny, 5-veined, apices ciliate; anthers 1.3-2.1 mm. Caryopses about 1.7 mm, concealed by the lemma and palea at maturity. 2n = 18, 36, 45, 48, 52, 53, 54, 56, 78.

Pennisetum polystachion is a polymorphic, weedy African species that has become established in the tropics and subtropics, including Florida. The U.S. Department of Agriculture considers it a noxious weed. Only Pennisetum polystachion subsp. setosum (Sw.) Brunken has been found in the Flora region. It differs from P. polystachion (L.) Schult. subsp. polystachion as indicated in the key below.