This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol1", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Mostly annual grasses with erect culms, flat leaf-blades, the inflorescence in spike-like panicles. Spikelets 1-flowered, or rarely with a second staminate flower, the basal bristles single or in clusters below the articulation of the rachilla, and therefore persistent. Scales of the spikelet 4, the three outer membranous, the third often subtending a palet and rarely a staminate flower; the inner or fourth scale chartaceous, often becoming indurated in fruit, subtending a palet of similar texture and a perfect flower. Stamens 3. Styles distinct, elongated. Stigmas plumose. Grain free, enclosed in the scales. [Greek, bristly-grass.]
Species about 35, in temperate and tropical regions. Type species: Setaria longiseta Beauv.
Bristles downwardly barbed.
Bristles upwardly barbed.
Inflorescence racemose; second scale shorter than the spikelet; bristles 5-16, involucrate.
Annual; spikelets exceeding 1 1/2" long; bristles yellowish brown.
Perennial; spikelets 1 1/2" long or less; bristles green, yellowish, or purple.
3. C. imberbis.
Inflorescence paniculate; second scale as long as the spikelet; bristles 1-3, not involucrate.
Fruiting scales dull, faintly rugose, obtuse, rather thin.
Inflorescence 1' - 3 1/2' long, 1/2' thick or less; spikelets about 1" long; bristles green.
Inflorescence 4'-9' long, 1/2'-2' thick; spikelets about 1 1/2" long; bristles usually purple.
Fruiting scales shining, perfectly smooth, very acute, hard.
1893. Ixophorus verticillatus Nash, Bull. Torr. Club, 22: 422.
1895. C. verticillata Scribn. Bull. U. S. Dep. Agr. Agrost. 4: 39.
Culms erect or decumbent, 1°-2° tall, more or less branched. Sheaths glabrous; blades 2'-8' long, 1/4'-1/2' wide, scabrous above; spikes 2'-3' long; spikelets about 1" long, equalled or exceeded by the downwardly barbed bristles; first scale less than one-half as long as the spikelet, 1-nerved; second and third scales 5-7-nerved, equalling the oval fourth one; palet of third scale empty.