Plants annual. Culms 20-80 cm, to about 1 mm thick, solid, branching above the base. Sheaths open; ligules of hairs; blades flat. Inflorescences terminal, panicles, 8-23 cm long, 0.8-2 cm wide, with pilose rachises; branches 0.5-1.5 cm, spikelets congested, shortly pedicellate, the pedicels subtended by a 3-10 mm, terete bristle; disarticulation below the glumes. Spikelets dorsally compressed, with 2 florets, lower florets usually sterile, upper florets bisexual. Lower glumes about 1/4 as long as the spikelets, 5-7-veined, subclasping; upper glumes slightly shorter than the spikelets, 11-19-veined, indurate at maturity, constricted at the base, auriculate above the point of constriction; lower lemmas longer than the glumes, membranous but somewhat indurate at the base; lower paleas usually present, short; upper lemmas indurate, finely transversely rugose, apiculate, margins clasping the paleas; upper paleas similar to the lemmas in length and texture; lodicules 2; anthers 3, purple; ovaries glabrous; style branches 2,free to the base. Caryopses ovate, plano-convex; embryos about 1/2 as long as the caryopses. x = 9. Name from the grass genus Setaria and the Greek opsis, appearance or likeness.