168 NORTH AMERICAN FLORA [VorumE 17 
Fruiting scale smooth and shining; stems from long 
. branching rootstocks. XXVII. DIsTIcHa. 
Spikelets with the first scale broadly winged. 
Wing lacerate ; spikelets glabrous. XXIII. FIMBRIATA. 
Wing entire; second scale papillose-hispid. XXXII. PECTINATA. 
B. Spikelets with long hairs 2-3 times their length; first scale with 2 
lateral nerves only, these extending at the base into decided projec- 
tions, the midnerve wanting and the internerve hyaline and very 
delicate. XXXIII. SacCHAROIDEA. 
I, ELONGATA. 
A single species in our range. 1. P. elongatum, 
II. STELLATA, 
Rachis-wings brown, not reticulate. 
Ciliate hairs on the spikelets of one kind. 2. P. cymbiforme. 
Ciliate i on the spikelets of two kinds, one much stouter than the 
other. 
Spikelets 2-2.5 mm. long, only the first scale ciliate, or the second 
short-ciliate toward the apex. 
_Spikelets 2.5-3 mm. long, the 2 outer scales ciliate. 
Rachis-wings yellowish-green, reticulate. 
P. heterotrichon, 
. P. stellatum, 
. PB. trachycoleon,. 
Cp 
III. DissectTa. 
Spikelets of 2 scales. 
Spikelets 2-2.5 mm. long; leaves smooth. 6. P. candidum. 
Spikelets 1.5-1.75 mm. long ; leaves very hispidulous. 7. P. scabrum, 
Spikelets of 3 scales. 
Rachis-internodes longer than the spikelets which are apparently in 
1 row. 8. P. longicuspe. 
-Rachis-internodes shorter than the spikelets which are apparently 
in 2 rows. 
Inflorescence of 2-4 racemes. 
Spikelets obtuse, about 2 mm. long, oval. 9. P. dissectum. 
Spikelets acute, 3-5 mm. long, elliptic. 10. P. acuminatum. 
Inflorescence of numerous, 7 or more, racemes. 
Spikelets glabrous, about 2 mm. long, obtuse ; racemes broad. 11. P. prostraium. 
Spikelets pubescent, 1.5-1.75 mm. long, acute or acutish; 
racemes slender. 12. PB. mucronaium. 
IV. SETACEA. 
Leaf-blades glabrous, or rarely with a few scatteredihairs on the margin. 
Blades narrowly linear, 3-5 mm. wide. 13. P. rigidifolium. 
Blades linear to lanceolate, 7 mm. wide or more. 
Spikelets glabrous. 14. P. epile. 
Spikelets pubescent. 15. P. Eggertit. 
Leaf-blades pubescent. ; 
Blades glabrous on the surface, at least the lower surface, or rarely 
with a few scattered long hairs, the margins conspicuously 
ciliate. 
‘Spikelets about 1.5 mm. long; leaves more numerous at the base 
of the stem. ‘ 
Spikelets 1.8 mm. long or more ;. leaves scattered. 
Blades firm, appressed-pubescent on the upper surface with 
16. P. longepedunculatum. 
short hairs. ; 17. P. stramineum, 
Blades thin, membranous, glabrous on the upper surface. 
Spikelets glabrous. 18. P. ciliatifolium. 
Spikelets pubescent. 19. P. Chapman, 
Blades densely pubescent on the’ surface, the margins sometimes 
ciliate. 
Spikelets less than 2 mm. long. 
Stems slender; leaf-blades narrow and scattered. 22. P. setaceum. 
Stems stout; leaf-blades broad, cordate at the base ; pubescence 
very long and copious. 25. P. debile. 
Spikelets 2 mm. long or more. ' 
Pubescence on foliage of copious, soft, short, appressed hairs, 
Stems prostrate, the lower blades 1 dm. long or less. 20. P. psammophilum, 
Stems erect, the lower blades 1.5 dm. long or more. 21. P. Bushii. 
Pubescence on foliage of long, stiff, spreading hairs. 
Stems long-hirsute below the racemes; basal sheaths usually 
glabrous or nearly so. 24. P. pubescens. 
Stems glabrous throughout; basal sheaths usually hirsute. 
Racemes on the main stem 1 or sometimes 2; spikelets 
glabrous; blades not thick. 23. P. Muhlenbergit. 
Racemes on the main stem 2 or 3; spikelets usually pubes- 
cent; blades thick. 26. P. supinum. 
V. PEDUNCULATA. 
Second scale not more than one half as long as the spikelet. 27. P. pedunculatum. 
Second scale as long as the spikelet or nearly so. 
