Panicum beecheyi is a cespitose perennial grass that typically reaches heights of 30–60 cm. Its culms are unbranched and may be either puberulent or glabrous, with nodes that are similarly glabrous or finely hairy. The leaves are simple, alternate, and arranged along the culm. Leaf blades measure 10–18 cm in length and 0.2–0.5 cm in width, and are either flat or loosely inrolled. Leaf surfaces range from glabrous to puberulent. The leaf sheaths are also glabrous or puberulent. The ligule consists of a short ciliate membrane, 0.7–1.6 mm long in total, with a membranous base (0.1–0.3 mm) and cilia 0.6–1.3 mm long. Stipules are absent. Inflorescences are open panicles 10–18 cm long with scabrous axes and spreading branches. Spikelets measure 2.4–3.4 mm long, are acuminate, and pilose. The glumes are as long as the spikelets; the first glume is slightly shorter than the second, with 5–7 nerves and pilose surfaces bearing hairs up to 2.5 mm long. The second glume has 7–9 nerves and is similarly acuminate and hairy. The first floret is sterile with a 7-nerved, glabrous lemma and a short palea (¼ the length of the spikelet). The fertile second floret is elliptic, glossy, and smooth, measuring 1.7–1.9 mm long and 0.5–0.7 mm wide, with three anthers each 1–1.3 mm long. The fruit is a caryopsis, typical of the grass family. It is found in dry, rocky, and open environments, typically at an elevation of approximately 900 meters.