Sheaths with papillose-based hairs, sometimes nearly glabrous; blades 4-10 cm long, 4-7 mm wide. Spikelets 3-3.2 mm long, subtending bristles 3-6.4 mm. Lower glumes 5-7-veined; upper glumes 5-7-veined. 2n = 36.

Setaria reverchonii subsp. firmula is endemic to the sandy prairies of southeastern Texas.