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 leaf-blades and terminal panicles, the pedicels thickened at the summit. Sheaths sometimes not split. Spikelets few-many-flowered. Two lower scales empty, unequal, acute; flowering scales rounded on the back, or sometimes compressed-keeled, 5-9-nerved, the apex usually 2-toothed, generally bearing an awn just below the summit; palet shorter than the scale, 2-keeled. Stamens usually 3. Stigmas sessile, plumose, inserted below a hairy cushion-like appendage at the top of the ovary. Grain adherent to the palet. [Greek name for a kind of oats.]
Lower empty scales 1-nerved, the upper 3-nerved.
Awns longer than the flowering scales; low annuals, 1 1/2° tall or less.
Flowering scales strigose, 4"-6" long.
Flowering scales sparsely hispidulous, 6" long or more.
Spikelets usually single on the long naked spreading branches.
Spikelets several on the branches which are divided and spikelet-bearing above the middle.
Awns shorter than the flowering scales, or wanting; perennials 1 1/2° tall or more.
Flowering scales awned.
Leaf-sheaths strongly retrorse-hirsute.
Leaf-sheaths glabrous or softly pubescent.
Blades 2"-6" wide; panicle branches more or less spreading or drooping.
Flowering scales pubescent on the margins only.
Flowering scales pubescent all over the back.
Blades less than 2" wide; panicle branches erect.
Flowering scales awnless or merely awn-pointed.
Lower empty scale 3-nerved, the second one 5-9-nerved (3-nerved in no. 9).
Flowering scales rounded on the back, at least below.
Perennials; flowering scales densely pubescent with long silky hairs.
Second empty scale 3-nerved; flowering scales s"-6" long.
Second empty scale 5-7-nerved; flowering scales about 4" long.
Flowering scales awned.
Flowering scales pubescent with soft appressed hairs, not dense.
Flowering scales glabrous, or minutely roughened.
Fruiting scales with strongly inrolled margins, the nerves obscure; leaf-sheaths
Fruiting scales with the margins not inrolled, the nerves prominent; leaf-sheaths softly and densely pubescent.
Spikelets broadly lanceolate, usually over 3" wide, 1 or sometimes 2 on
the longer branches.
Spikelets lanceolate, usually less than 3" wide, several on the longer
Awns bent near the base, divergent.
Spikelets less than 2l/2" broad in flower.
Spikelets exceeding 2 1/2" broad in flower.
Flowering scales awnless or awn-pointed, nearly as broad as long.
Flowering scales compressed, keeled.
Flowering scales pubescent; awn 2"-3" long.
Flowering scales minutely roughened; awn less than 1" long or wanting.