Plants with well‑developed, scaly rhizomes, forming tufts. Flowering stems 40–100 cm long, erect or ascending, sometimes from spreading bases, dull, minutely hairy between the nodes, at least below the nodes. Leaf sheaths glabrous or roughened, rounded to slightly angled on the back, the ligule 0.4–1.2 mm long. Leaf blades 2–20 cm long, 1–6 mm wide, flat, glabrous or roughened. Inflorescences dense, spikelike, terminal and lateral panicles 2–8(–12) cm long, linear in outline, the base usually stalked and not enclosed by the subtending leaf sheath, the branches short, appressed to the main axis or nearly so. Spikelets 2.2–3.2 mm long (excluding the awns), short‑stalked, the stalks mostly shorter than the spikelets. Glumes usually about the same length, the body (1.2)1.8–3.0 mm long, variable, but mostly slightly shorter than the floret, lanceolate to narrowly triangular, only slightly overlapping at the base, the margins relatively straight and tapered gradually to the sharply pointed tip, strongly 1‑nerved, awnless or with an awn 0.2–0.5 mm long. Lemma with the body 2.3–3.2 mm long, lanceolate, the tip sharply pointed, with an awn 3–18 mm long, with a tuft of short hairs at the base, otherwise roughened along the midnerve. Anthers (0.4–)0.6–0.9 mm long. Fruits 1.4–1.8 mm long. 2n=40. July–October.

Scattered nearly throughout Missouri (northeastern U.S. west to South Dakota, Nebraska, and Texas; Canada). Bottomland forests, mesic upland forests, ledges of bluffs, margins of ponds and sinkhole ponds, banks of streams and spring branches, acid seeps, fens, and, uncommonly, dry upland forests and glades, on both calcareous and acidic substrates; also pastures and roadsides.

Pohl (1969) determined that the awnless f. attenuata (Scribn.) E.J. Palmer & Steyerm. was based upon a specimen of the related M. frondosa and placed this taxon in synonymy under that species. Thus, all plants of M. sylvatica produce awned lemmas.