Eragrostis atropioides is a perennial grass that forms loose tufts characterized by hard, scaly rhizomes up to 7 cm long. The culms are erect and stiff, 1-1.5 meters tall, glabrous, and slightly scabrous below the panicles. The leaves are simple and alternate, with blades measuring 30-40 cm long and 4-6 mm wide, with a long-acuminate apex. The upper surfaces of the leaves are scabrous, while the lower surfaces are glabrous. The leaf sheaths are glabrous but pilose at the throat and along the margins, especially in the sterile shoots. The ligule presents as a pilose ridge with hairs approximately 5 mm long, complemented by silky hairs 4-6 mm long. Stipules are absent. The inflorescences are paniculate, erect, and contracted but not quite spike-like, measuring 25-50 cm long and about 24 cm wide. The inflorescence branches are several per node, 0-10 cm long, and appressed with pilose nodes. The spikelets are linear, many-flowered, and can be up to 2.5 cm long, with a glabrous rachilla. The glumes are slightly unequal, narrowly ovate, 3-4 mm long, and scabrous on the keel with an acuminate apex. The lemmas are pale or purplish green, closely imbricate, 2-3 mm long, and glabrous except for being minutely scaberulous at the apex, which is obtuse to erose. The palea is persistent, 2-3 mm long, with the upper portion of the keel ciliate and an obtuse and usually erose apex. The fruit is a dark red caryopsis, narrowly ovoid to fusiform, and 0.8-1 mm long. It occurs in dry, exposed sites between 120-1920 meters.