MANUAL OF THE GRASSES OF THE UNITED STATES 615 



9b. Sheaths pubescent. 



Pubescence ascending or appressed. 



Spikelets 3 to 3.2 mm long; first glume conspicuously remote. 



62. P. MALACON. 



Spikelets 3.5 to 4 mm long; first glume not remote. 



93. P. OLIGOSANTHES. 



Pubescence spreading, sometimes sparse. 



Plants robust, about 1 m tall; blades usually 2 cm or more wide. 



108. P. CLANDESTINUM. 



Plants rarely more than 50 cm tall; blades rarely more than 1.5 cm 

 wide. 

 Panicle about as wide as long; blades ascending or spreading. 

 Spikelets attenuate at base, 3.5 to 4 mm long. 



See 14. Pedicellata. 



Spikelets not attenuate at base, not more than 3.3 mm long. 



Spikelets 3.2 to 3.3 mm long; blades firm; sheaths, or some 



of them, more or less hispid. _ 92. P. scribnerianum. 



Spikelets not more than 3 mm long; blades rather thin; 



sheaths, or some of them, glabrous or sparsely hispid. 



91. P. HELLERI. 



Panicle narrow, the branches erect (sometimes ascending in P. 

 vrilcoxianum) , or spreading at anthesis only; blades erect. 

 Spikelets not more than 3 mm long; blades not more than 6 mm 



wide 89. P. wilcoxianum. 



Spikelets 3.7 to 4 mm long; blades 8 to 20 mm wide. 



Blades papillose-hispid 95. P. leibergii. 



Blades glabrous on both surfaces 96. P. xanthophysum. 

 6b. Spikelets less than 3 mm long. 



10a. Blades elongate, not more than 5 mm wide; secondary panicles at the 

 base only or wanting. 

 Culms single or few in a tuft; spikelets turgid, 2.7 to 3 mm long. 



6. P. PERLONGUM. 



Culms in large tufts; spikelets not turgid, not more than 2.7 mm long. 



Sheaths pilose 7. P. linearifolitjm. 



Sheaths glabrous 8. P. werneri. 



10b. Blades usually not elongate; secondary panicles not at the base. 

 11a. Spikelets attenuate at base, mostly prominently pustulose. Blades 

 narrow, stiff, strongly nerved, tapering from base to apex. 

 Nodes bearded; plants grayish-villous. Autumnal blades flat. 



Spikelets 2 mm long 15. P. chrysopsidifolium. 



Spikelets 2.5 to 2.8 mm long 16. P. consanguineum. 



Nodes not bearded; plants villous only at the base, or nearly glabrous. 

 Autumnal blades flat; lower panicle branches spreading or reflexed. 



17. P. ANGUSTIFOLIUM. 



Autumnal blades involute; lower panicle branches more or less 

 ascending. 

 Plants glabrous or nearly so; autumnal culms erect. 



Spikelets subsecund along the suberect panicle branches. 



21. P. NEURANTHUM. 



Spikelets not subsecund; panicle loose and open. 



20. P. OVINUM. 



Plants pubescent, at least on the lower half. 



Spikelets about 2.4 mm long; vernal blades 7 to 12 cm long; 



autumnal blades not falcate 19. P. arenicoloides. 



Spikelets not more than 2 mm long; vernal blades 4 to 6 cm 



long; autumnal blades falcate 14. P. aciculare. 



lib. Spikelets not attenuate at base. 



12a. Sheaths retrorsely pilose. Blades soft and lax. 



Blades ciliate and more or less pilose on the surface; spikelets 2 mm 



long 10. P. xalapense. 



Blades glabrous or nearly so on the surface and margin; spikelets 



2.2 mm long 9. P. laxiflorum. 



12b. Sheaths not retrorsely pilose. 



13a. Ligule manifest, mostly 2 to 5 mm long, at least 1 mm long. 

 Sheaths, or all but the lowest, glabrous; spikelets not more than 

 1.6 mm long. 

 Panicle narrow, one-fourth to one-third as wide as long. 



38. P. spketum. 



