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..
Usually tall annual grasses, with flat leaf-blades and numerous spikes forming a simple panicle. Spikelets usually 2-many-flowered, flattened, alternating in two rows on one side of the rachis. Scales 4-many; the 2 lower empty, keeled, shorter than the spikelet; the flowering scales keeled, 3-nerved. Palet 2-nerved. Stamens 3. Styles distinct. Stigmas plumose. Grain free, enclosed in the scale and palet. [Greek, in allusion to the slender spikes.]
Flowering scales 3/4" long, the hairs on the nerves long and copious.
Flowering scales less than 1/2" long, the hairs on the nerves short and scant.
Culms 1°-3° tall, erect, branched, smooth and glabrous. Sheaths shorter than the internodes, smooth and glabrous; ligule short, lacerate-toothed; blades 2'-8' long, l"-3" wide, scabrous; spikes numerous, slender, rigid, spreading or ascending, the lower 2'-6' long; spikelets usually 3-flowered, about 1" long, the empty scales shorter than the spikelet, acute, 1-nerved, slightly scabrous on the keel; flowering scales 2-toothed at the apex, ciliate on the nerves.
In dry or moist soil, Virginia to Illinois, and California, south to Florida and Mexico. Also in tropical America. July-Sept.
Culms tufted, branching at the base, 8'-16' tall, rarely taller; lower sheaths sparingly pilose; blades 1 1/2'-4' long; spikes numerous, finally spreading, up to 2' long, rarely longer; spikelets 1 1/4"- 1 1/2" long, the scales 5 or 6, the outer 2 subulate, acuminate, awn-pointed, usually about equal, or the first shorter than the second, which reaches or extends beyond the apex of the second flowering scale.
In sandy river bottoms, Illinois to Oklahoma and Louisiana. Sept. and Oct.