70 POACEAE 
Spikelets glabrous: 
2mm. long: leaves scattered along the stem. 
1.5 mın. long: leaves crowded at the base of the stem: 
Upper surface of the blades glabrous; marginal hairs 
less than 1 mm. long. 
Upper surface of the leaves pubescent with short 
hairs; marginal hairs about 2 mm. long. 
**Blades naked on the margins, or rarely with a few scattered hairs. 
Racemes 1-3. 
Uppermost sheath pubescent on the overlapping margin. 
Leaf-blades lanceolate; spikelets orbicular-obovate, the 
first and second scales strongly pubescent. 
Leaf-blades linear, rigid, long and narrow; spikelets oval, 
the first scale sparingly pubescent. 
Uppermost sheath glabrous on the margin. 
Spikelets glabrous. 
Spikelets with the first scale pubescent. 
Leaf-blades linear, narrow, becoming involute; spike- 
lets elliptic. 
Leaf-blades linear-lanceolate, broad, flat; 
broadly obovate. 
Racemes 6-12. 
2. Leaf-blades very pubescent on both surfaces. 
Stem long-hirsute below the raceme; basal sheaths glabrous or 
nearly so. 
Stem glabrous throughout; basal sheaths usually hirsute. 
Spikelets 1-1.5 mm. long. 
Stems slender; blades narrow and scattered. 
Stems stout; blades broad, crowded at the base; pubescence 
very leng and copious. 
Spikelets 2-2.25 mm. long. 
Raceme on the main stem 1, or sometimes 2 together ; spike- 
lets glabrous; leaf-blades not thick. 
Racemes on the main stem 2 or 8; spikelets usually more or 
less pubescent ; leaf-blades thick. 
b. Stems simple, no raceme-bearing branches from the uppermost sheath. 
1. Racemes 2-several, scattered, never in pairs. 
*Stems tufted. 
Spikelets rounded or obtuse at the apex, not ciliate on the mar- 
spikelets 
gins. 
2Spikelets convex on one side. 
Spikelets 3 mm. long or less. 
Spikelets singly disposed. 
Spikelets oval, 14 as thick as broad or more, the outer 
scales firm. 
Spikelets 2 mm. long, the flowering scale deep seal 
brown at maturity. 
Spikelets 2.5 mm. long, the flowering scale yellow- 
ish white at maturity. 
Leaf-sheaths glabrous. 
Blades short ; racemes usually 2 or 3. 
Blades elongated ; racemes usually 3-5. 
Leaf-sheaths hirsute, at least on the margins. 
Blades short, glabrous on the lower surface. 
Sheaths hirsute only on the margins, or 
the basal ones sometimes sparingly so 
on the surface. 
Sheaths broad and much compressed, 
densely hirsute all over with very 
long weak hairs. 
Blades elongated, more or less hirsute on 
both surfaces. : 
Spikelets circular or nearly so, about L4 as thick as 
broad, the outer scales very thin. ` 
Spikelets in pairs. 
Mature flowering scale white or yellowish. 
Spikelets 2 mm. long or less; stems slender. 
Spikelets obovate, 1.5 mm. long, pubescent with 
ope glandular-tipped hairs. 
Spikelets elliptie, 2 mm. long, sparsely pubes- 
cent with long appressed hairs. 
Spikelets 2.5-3 mm. long ; stems usually stout. 
Spikelets pubescent. 
Spikelets glabrous. 
Stems rooting at the lower nodes; blades 
thin, long ; racemes 4-8. 
Stems not rooting at the lower nodes; blades 
firm, short; racemes 3, rarely 4. 
Mature Verse scale deep seal brown. 
Rachis broadly winged, wider than the spikelets 
which are about 2 mm. long. 
Rachis narrowly winged, much narrower than the 
spikelets which are 2.5-3 mm. long. 
Spikelets more than 3 mm. long. 
Racemes long and strictly erect, or short and ascending. 
Leaf-blades short ; racemes short and ascending. 
Sheaths glabrous or nearly so. 
Sheaths densely hirsute. 
21. 
26. 
31. 
32. 
7. P. ciliatifolium. 
. P. Kentuckiense. 
. P. longepedunculatum. 
. P. Eggertii. 
. P. rigidifolium. 
SP epue. 
. P. elatum. 
. P. latifolium. 
. P. gracillimum. 
. P. pubescens. 
. P. setaceum. 
. P. villosissimum. 
. P. Muhlenbergii. 
. P. dasyphyllum. 
P. scrobiculatum. 
. P. laeve. 
. P. angustifolium. 
. P. australe. 
. P. longipilum. 
P. praelongum. 
. P. circulare. 
. P. Simpsonii. 
. P. Blodgettii. 
. P. Hallii. 
P. laeviglumis. 
P. geminum. 
. P. Boscianum. 
. P. plicatulum. 
5. P. difforme. 
36. 
P. altissimum. 
