Awns not articulated to the scale.

Central awn coiled at the base.

First scale usually equalling or sometimes slightly shorter than the second scale, which is

commonly 3 1/2"-4 1/2" long.

1.

A. dichotoma.

First scale much shorter than the second (often but little more than l/2 as long), which is 5"-8" long.

Lateral awns short, straight and erect, 1/2"-1" long, the central awn usually more than

five times their length, its straight portion 2l/2"-4" long.

2.

A. Curtissii.

Lateral awns more or less spreading, usually a little spiral at the base, the central awn

from 1/2 again to twice their lenth, its straight portion s"-8" long.

3.

A. basiramea.

Central awn not coiled of the base.

Panicle narrow, linear to oblong, branches short (or long in no. 13), erect or ascending.

Central awns and sometimes the lateral ones also stronlgy reflexed, the bend semicircular.

4.

A. ramosissima.

Central awn from erect to spreading with no such bend at the base.

First scale much shorter than the second, usually about 1/2 as long.

Spikelets crowded, 4 - 6 on the short branches, which are spikelet-bearing to the

base or nearly so.

5.

A. fasciculata.

Spikelets not crowded, usually 1-3 on branches naked at the base.

Second scale of spikelet 8" long or less, equalling or exceeding flowering scale.

Panicle simple or nearly so, its branches bearing 1 spikelet; culms com-

monly naked above.

6.

A. Fendleriana.

Panicle compound, its branches bearing 2 or more spikelets; culms usually

leafy.

7.

A. Wrightii.

Second scale of the spikelet 10" long or more, 1 1/2-2 times as long as the

flowering scale.

8.

A. longiseta.

First scale from a little shorter than to exceeding the second.

Spikelets exceeding 10" long; first scale 5-7-nerved.

9.

A. oligantha.

Spikelets less than 8" long; first scale 1-3-nerved.

Leaf-sheaths glabrous or sparsely pubescent.

First scale generally shorter than or equalling the second.

Flowering scale 2l/2"-2" long, its central awn usually 3"-5" long.

10.

A. gracilis.

Flowering scale 3 1/2"-4 1/2" long, its central awn exceeding in length.

11.

A. intermedia.

First scale exceeding the second.

12.

A. purpurascens.

Leaf-sheaths, at least the lower ones, densely wooly.

13.

A. lanosa.

Panicle diffuse and open, the branches very long and widely spreading.

14.

A. divaricata.

Awns articulated to the scale, united at the base into a spiral column.

Column conspicuous, 3" long or more.

15.

A. tuberculosa.

Column inconspicuous, 1" long or less.

16.

A. desmantha.