This species seems to be local but abundant where it is found. I have seen acres of it in Newton County in the old lake bed, and in Noble County it forms large colonies on the former bottom of Tippecanoe Lake. Local in moist, sandy soil on interdunal flats about Lake Michigan, in moist sandy, prairie habitats, and on moist sandy borders of lakes.
Annual herb 15 cm - 0.87 m tall Leaves: along the culm, the open sheaths shorter than the internodes and hairless or sparsely soft-haired with hairy throats and hairless collars. The ligules are made of hairs to 0.5 mm long, and the blades are light green, 5 - 14 cm long, 1 - 2 mm wide, flat or with margins somewhat rolling toward the upper surface of the midveins (involute). Inflorescence: terminal, 6 - 22 cm long, 1 - 6 cm wide, nodes hairless or with hairs to 0.3 mm long. The primary branches are 1 - 4 cm long, appressed to erect, and sometimes spreading at the tip. Fruit: a spindle-shaped caryopsis with a linear scar. Culm: erect to spreading, usually bent at the nodes (geniculate) near the base, occasionally nearly prostrate, 15 cm - 0.65 m long, often highly branched. Spikelets: two to five per branch. Glumes: nearly equal, 4 - 11 mm long, thin, single-veined, with a pointed tip. Florets: one per spikelet, with one or three anthers. Lemma: gray to dark purplish brown, usually horizontally banded or mottled, 3.5 - 10 mm long, spindle-shaped with a slightly narrowed tip, rolled up longitudinally (convolute), rough-hairy or hairless, with three veins and three awns. The awns are usually unequal, with the central awn 8 - 27 mm long and erect to reflexed, and the lateral awns often 6 - 18 mm long and erect to horizontal. Palea: shorter than the lemma, two-veined.
Similar species: The typical variety of Aristida longispica has shorter central awns (1 - 14 mm) and shorter (to 5 mm) or missing lateral awns.
Flowering: August to September
Habitat and ecology: Sandy soil.
Occurence in the Chicago region: native
Etymology: Aristida comes from the Latin word arista, meaning awn. Longispica means "with a long spike." Geniculata means "with a knee-like bend."