Spikelets 1-flowered, not jointed on the pedicels. Outer glumes unequal, often bristle-pointed; the flowering glume tipped with three awns; the palet much smaller. Otherwise much as in Stipa.—Culms branching; leaves narrow, often involute. Spikelets in simple or panicled racemes or spikes. Grain linear. All grow in sterile, dry soil, and all ours have the awns naked and persistent, and flower late. (Name from arista, a beard or awn.)
[*] Awns separate to the base, not jointed with the glume.
[+] Awns very unequal; the much shorter or minute lateral ones erect, the elongated middle one horizontal or turned downward; low (5–18´ high) and branching, mostly tufted annuals, and the spikelets in nearly simple spikes.
[++] Middle awn more or less coiled.
1. A. ramosíssima, Engelm. Culms much branched; spikes loose, usually exserted; lower glumes 6–10´´ long, exceeding the upper, usually rather strongly 3–5-nerved; middle awn 1´ long, soon abruptly hooked-recurved, the lateral ones 1–3´´ long.—Dry prairies of Ill., Ky., and Mo.—Also var. uniaristàta, Engelm., with the lateral awns wanting.
2. A. basiràmea, Engelm. Spikes closer, mostly enclosed at base, at all the lower nodes (even to the base of the culm) very short and sessile; lower glumes 4–8´´ long, mostly thin and 1-nerved or rather faintly 3-nerved; middle awn very slender, 6´´ long, the lateral 2´´ long.—Ill. to Neb. and Minn.
3. A. dichótoma, Michx. (Poverty Grass.) Culms low, very slender, much branched throughout, ascending; spikelets in narrow strict simple or compound spikes; lower glumes nearly equal (3–4´´ long), longer than the flowering glume and fully equalling its minute lateral awns (or unequal and shorter, in var. Curtíssii, Gray), the soon reflexed middle awn about as long.—Dry, sandy or gravelly fields; common, Maine to Ill., and southward.
[++][++] Middle awn nearly straight (not coiled).
4. A. grácilis, Ell. Culms slender, erect (6–18´ high), naked above and terminating in a slender raceme- or spike-like virgate panicle; lower glumes 1-nerved, about the length of the upper, the exserted lateral awns varying from one third to fully half the length of the horizontally bent middle one: or in var. depauperàta, from one fifth to one third its length.—Sandy soil, coast of Mass., and from Ill. southward.—Middle awn 3–9´´ long in the ordinary forms, but not rarely shorter, and very variable often on the same plant.
[+][+] Awns all diverging and alike, or the lateral ones moderately shorter, rarely at all coiled.