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 tufted grasses with flat or bristle-like leaves and paniculate inflorescence. Spikelets 1-flowered. Scales 3; the 2 outer empty, membranous, keeled, acute; the third shorter, obtuse, hyaline, sometimes bearing a dorsal awn, subtending a perfect flower; palet shorter than the scale, sometimes minute or wanting. Stamens usually 3. Styles distinct, short. Stigmas plumose. Grain free, enclosed in the scale. Seed adherent to the pericarp. [Name Greek, referring to the field habitat of many species.]
A genus of about 100 species, distributed throughout the world, numerous in temperate regions; 15 others are found in western North America. Type species: Agrostis alba L.
Palet conspicuous, at least one-half as long as the scale.
Panicle open in flower, branches long and spreading; an upland grass. 1. A. alba.
Panicle dense and contracted, spike-like, its branches short and appressed; a grass of brackish
marshes and wet sands.
Palet inconpicuous, minute, or wanting.
Branches of the contracted panicle short, spikelet-bearing to the base.
Branches of the panicle slender, naked below.
Flowering scale awned.
Awn flexuous, barbellate, twice the length of the 3/4," spikelet.
Awn stouter, glabrous, rigid, usually bent, not twice the length of the spikelet.
Branches of the panicle usually ascending; spikelets 1" long.
Culms 1°-2° tall; panicle exceeding 2' long.
Branches of the mature panicle spreading; spikelets 1 1/4'-1 1/2" long.
Awn exserted; panicle branches glabrous or hispidulous.-
Awn short; panicle branches hispid.
Flowering scale awnless, or very rarely with a short awn.
Culms weak, decumbent or prostrate at the base; blades lax.
Culms and blades erect.
Branches of the panicle capillary, elongated, usually dividing above the middle, the spikelets often crowded at the extremities.
Spikelets 3/4"-1" long; blades short.
Spikelets 1 1/4"-1 1/2" long; blades elongated.
Branches of the panicle not elongated, usually dividing at or below the middle.
Spikelets about 1" long; a grass of low elevations.
Spikelets 1 1/4"- 1 1/2" long; a high mountain grass.