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..
Perennial or rarely annual grasses, with flat or convolute leaf-blades and open or contracted panicles. Spikelets generally small, 1-flowered, occasionally 2-3-flowered. Scales in the 1-flowered spikelets 3, membranous; the 2 outer empty, the first somewhat shorter; the third scale equalling or longer than the empty ones; palet 2-nerved. Stamens 2-2,. Styles very short, distinct. Stigmas plumose. Grain free, and often early deciduous. [Greek, referring to the deciduous grain.]
About 100 species, in tropical and temperate regions, very numerous in America. Besides the following, several others occur in the southern and western United States. Type species: Agrostis indie a L.
Spikelets 2" long; flowering scale pubescent.
Spikelets 1 1/4"-1 1/2" long; flowering scale glabrous.
Plants tufted; no rootstocks.
Panicle occupying but a small part of the plant.
Leaves glabrous or nearly so.
Flowering scale pubescent.
Palet long-acuminate, much longer than the flowering scale
Palet simply acute, about as long as the flowering scale.
Flowering scale glabrous.
Spikelets 2" long; inflorescence slender.
Spikelets 2 1/2"-3" long; inflorescence stout.
Leaves, at least the lower ones, papillose-hirsute.
Panicle occupying 1/3-1/2 of the plant.
Plants with long creeping rootstocks.
Panicle open, its branches spreading, at least at maturity (sometimes contracted in no. 15). Annuals.
Empty scales but little shorter than the flowering scale, usually pubescent.
Empty scales 1/2 as long as the flowering scale, glabrous.
Culms tufted; no rootstocks.
Spikelets 1" - 1 1 /2" long; empty scales ovate to lanceolate.
Panicle branches verticillate.
Spikelets 3/4" long, green.
Spikelets 1 1/4"-1 1/2" long, purple.
Panicle branches alternate.
Leaf-sheaths naked, or sparingly ciliate at the throat; panicle usually exserted.
Leaf-sheaths densely pilose at the throat; base of the panicle generally included.
Spikelets 2"-3" long; first scale subulate, much narrower than the second.
Culms from long running rootstocks.
First scale of the spikelet 1/2 as long as the second or less.
First scale about equalling the second.
Culms erect, simple; leaf-blades elongated.
Culms decumbent and branched below; leaf-blades short.