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..
Annual or perennial grasses with flat or convolute leaf-blades and numerous spikelets in one-sided spikes. Spikelets 1-2-flowered, arranged in two rows on one side of a flat rachis, the rachilla extended beyond the base of the flowers, bearing 1-3 awns and 1-3 rudimentary scales. Two lower scales empty, acute, keeled; flowering scale broader, 3-toothed, the teeth awn-pointed or awned; palet hyaline, entire or 2-toothed. Stamens 3. Styles distinct. Stigmas plumose. Grain oblong, free. [In honor of Claudius Boutelou, a Spanish botanist.]
Rachilla bearing the rudimentary scales and awns glabrous; second scale strongly papillose-hispid
on the keel. _
Rachilla bearing the rudimentary scales and awns with a tuft of long hairs at the apex; second
scale scabrous and sparingly long-ciliate on the keel.
B. hirsuta Lag. Var. Cienc. y Litter. 2: Part 4, 141. 1805.
Culms 6'-2o' tall, erect, simple or sometimes sparingly branched at the base, smooth and glabrous. Sheaths mostly at the base of the culm, the lower short and crowded, the upper longer; ligule a ring of short hairs; blades 1'-5' long, 1" wide or less, erect or ascending, flat, scabrous, sparingly papillose-hirsute near the base, especially on the margins; spikes 1-4, Y-2' long, usually erect or ascending, the rachis extending beyond the spikelets into a conspicuous point; spikelets numerous, 2 1/2-3" long, pectinately arranged; first scale hyaline, shorter than the membranous second one, which is strongly papillose-hirsute on the keel; third scale pubescent, 3-cleft to the middle, the nerves terminating in awns; rachilla without a tuft of hairs under the rudimentary scales and awns.
Atheropogon oligostachyus Nutt. Gen. 1: 78. 1818.
Culms 6' -18' tall, erect, simple, smooth and glabrous. Sheaths shorter than the internodes; ligule a ring of short hairs; blades 1'-4' long, 1" wide or less, involute, at least at the long slender tip, smooth or scabrous; spikes 1-3, 1'-2' long, often strongly curved, the rachis terminating in a short inconspicuous point; spikelets numerous, pectinately arranged, about 3" long; first scale hyaline, shorter than the membranous second one, which is scabrous and sometimes long-ciliate on 'the keel, and sometimes bears a few papillae; third scale pubescent, 3-cleft, the nerves terminating in awns; rachilla with a tuft of long hairs under the rudimentary scales and awns.