Plants annual, with a soft base. Flowering stems 15–60 cm long, glabrous. Leaf blades 1–2 mm wide, flat to strongly inrolled, glabrous or sparsely hairy on the upper surface. Leaf sheaths glabrous or nearly so. Lower glume 12–25 mm long, somewhat shorter than the upper glume, 3‑ or 5‑nerved, roughened along the midnerve, the tip sharply pointed or with an awn 1–4 mm long. Upper glume with the body 15–31 mm long, 1‑ or 3‑nerved, roughened along the midnerve, the tip divided, with an erect awn 7–17 mm long arising from between 2 slender teeth 1–3 mm long. Lemmas with the body 10–22 mm long, glabrous or roughened along the midnerve, the awns persistent, not jointed at the tip of the lemma (the awns arise as a continuation of the lemma tip, without a cross‑line), circular in cross‑section, the central awn (20–)35–70 mm long, somewhat longer than to less commonly about equal to the lateral awns in length, straight to somewhat curved outward, but not coiled, the lateral awns (20–)25–65 mm long, erect to somewhat bent outward. 2n=22. June–October.

Common throughout Missouri (eastern U.S. and adjacent Canada west to South Dakota, Texas, and Arizona). Glades, tops of bluffs, fallow fields, pastures, roadsides, railroads, and dry, disturbed areas.

This is the commonest species of three‑awn in the state. A few Missouri specimens from Jackson and St. Clair Counties and St. Louis were annotated by Kelly Allred (New Mexico State University) as belonging to a variant of A. oligantha with the central and lateral awns of the lemmas only 20–30 mm long and of nearly equal length. Apparently, populations of short‑awned individuals occur sporadically within the species’ range. Whether these uncommon plants are merely morphological variants of A. oligantha or reflect past hybridization between it and some other species, such as A. ramosissima, cannot be determined without further study. The name A. ramosissima var. chaseana Henrard applies to this variant (Allred, 1986, and personal communication), but it has not yet been transferred to A. oligantha.