Plants perennial; cespitose. Culms 40-100 cm. Sheaths villous
distally, margins ciliate; ligules about 1 mm, densely ciliate, hairs white;
blades 15-30 cm long, 5-8 mm wide, both surfaces villous. Panicles
10-20 cm, loosely spicate; bristles usually solitary, 10-20 mm. Spikelets
2.8-3 mm. Lower glumes about 1/3 as long as the spikelets, broadly ovate,
3-veined; upper glumes nearly equaling the spikelets, 5-7-veined; lower
lemmas equaling the upper lemmas, 5-veined; lower paleas about 1/5
as long as the upper paleas, lanceolate; upper lemmas finely and transversely
undulate-rugose basally, striate and punctate distally; upper paleas similar,
ovate-lanceolate. 2n = 54.
Setaria villosissima is a rare species that grows on granitic soils in
southwestern Texas and northern Mexico. Hitchcock's (1951) report of S. villosissima
growing in Arizona was based on misidentification of a specimen of S.
leucopila (Reeder 1994). The villous sheaths and blades and large spikelets
of S. villosissima aid in its identification.