Eragrostis deflexa is a perennial with distinct growth and reproductive features. It has tufted, firm, and slender culms, typically erect but somewhat decumbent at the base, ranging from 40-100 cm in height and glabrous. The leaves are simple and alternate, with blades measuring 10-30 cm long and 1-3(-4) mm wide, either flat or involute. They have parallel veins and sheaths that are glabrous but pilose at the throat and on the collar. The ligule is ciliate, approximately 0.2 mm long, and stipules are absent. The flowers are part of a paniculate, open, oblong, and erect inflorescence, measuring 24-40 cm long and 6-15 cm wide. The branches are widely spaced, fasciculate, and become spreading or deflexed, with the lowest primary branches being 5-9 cm long and scabrous. The lower axils are densely pilose. Spikelets (pictured) are 4-7-flowered and 5-8 mm long, with somewhat flexuous pedicels. The lateral ones are 2-4 mm long and somewhat compressed, and the rachilla is flexuous and glabrous. Glumes are subequal, 2.5-3 mm long, with a scaberulous keel and acuminate apex. The lemmas are loosely imbricate, exposing the rachilla, rather turgid, and approximately 2.5 mm long and 0.7 mm wide. The lateral nerves are faint and finely scaberulous on the upper part of the keel and sides near the apex. The palea is nearly as long as the lemma, with finely scaberulous keels. The fruit is a caryopsis, dark reddish-brown, oblong, laterally compressed, and measures 0.9-1.1 mm in length. It is found in dry forests and shrublands on old lava flows and cinder cones.