Plants perennial; cespitose, not rhizomatous. Culms 25-95 cm. Sheaths
rounded below, upper margins sometimes sparsely hispid-ciliate, apices hairy,
hairs to 5 mm; ligules 0.2-0.3 mm; blades 8-22 cm long, 2-5 mm wide,
flat or involute, glabrous abaxially, scabridulous adaxially, margins scabrous,
sometimes sparsely hispid. Panicles 5-30 cm long, 0.4-1.6 cm wide, narrow,
contracted; lower nodes with 3 or 5 branches; primary branches 0.3-2
cm, appressed or spreading to 20° from the rachis, spikelet-bearing to near
the base; secondary branches appressed; pedicels 0.2-2.5 mm, appressed,
scabridulous. Spikelets 2.8-3.8 mm, purplish-red. Glumes unequal,
linear-lanceolate to lanceolate or ovate, hyaline to membranous; lower glumes
0.9-3 mm; upper glumes 2.9-3.8 mm, subequal to the florets; lemmas
2.9-3.8 mm, ovate, membranous, glabrous, acute; paleas 2.9-3.8 mm, ovate,
membranous; anthers 1.5-2 mm, yellowish to purplish. Fruits 1.8-2.3
mm, ellipsoid, somewhat laterally flattened, rugulose, reddish-brown. 2n
= 60.
Sporobolus purpurascens grows in oak scrub, prairie grasslands,
and sandy sites near railroad crossings and roadsides, at elevations from 2-300
m. It extends from southern Texas through eastern Mexico, the West Indies, and
Central America to Brazil.