Plants perennial; cespitose, bases knotty, without rhizomes. Culms 40-100 cm tall, 1-4 mm thick at the base, erect, branching at the base, shoots becoming thickened and somewhat fan-shaped upwards. Leaves cauline; sheaths mostly longer than the internode, mostly or completely glabrous, sometimes pilose, particularly along the margins and at the throat, remaining intact at maturity; collars glabrous or pilose; ligules about 0.2 mm; blades 10-25 cm long, 1-3 mm wide, usually flat, usually lax, sometimes sinuous to curling at maturity, glabrous, pale green, drying brownish. Inflorescences paniculate, (15)20-55 cm long, 0.5-2(3) cm wide, often nodding; nodes glabrous, sometimes scabrous, lower nodes usually associated with more than 2 spikelets; primary branches 1-5 cm, tightly appressed to loosely ascending, without axillary pulvini, with 1-8 spikelets. Spikelets appressed. Glumes 5-10 mm, lower glumes from 3/4 as long as to 1-4 mm longer than the upper glumes, glabrous or sparsely appressed-pubescent, 1-2-veined, 1-keeled, tan to purplish, unawned or the awns no longer than 1 mm; calluses 0.4-0.8 mm; lemmas 4-8 mm, glabrous, mostly light tan or gray, often spotted or banded, beak not twisted, junction with the awns not evident; awns 8-25 mm, equal or subequal in length, curved, arcuate, or spirally coiled at the base, not disarticulating at maturity; central awns sometimes thicker than the lateral awns, erect to arcuate-reflexed; lateral awns straight and erect, ascending, or divergent; anthers 1 or 3, 1-1.5 mm, brown. Caryopses 3-5 mm, chestnut brown. 2n = unknown.
Del., D.C., Wis., W.Va., Fla., N.J., Conn., Mass., R.I., La., N.C., Nebr., Tenn., S.C., Pa., Ind., N.Y., Va., Ont., Ala., Ark., Ill., Ga., Miss., Kans., Mich., Md., Okla., Tex., Ohio, Mo., Ky.
|1||Central awns divaricate to reflexed, about twice as thick at the base as the lateral awns||Aristida purpurascens var. virgata|
|1||Central and lateral awns divergent, all about the same thickness at the base.||> 2|
|2||Lower glumes usually longer than the upper glumes; awns straight or only slightly contorted at the base; blades 1-3 mm wide, often curling||Aristida purpurascens var. purpurascens|
|2||Lower glumes shorter than or equal to the upper glumes; awns spirally contorted at the base; blades mostly about 1 mm wide, usually not curling||Aristida purpurascens var. tenuispica|