POACEAE. 



15 



2. P. philadelphicum. 



3. P. flexile. 



4. P. miliaceum. 



5. P. dichotomiflorum. 



6. P. virgatum. 



7. P. agrostoides. 



8. P. longifolium. 



9. P. stipitatum. 

 10. P. anceps. 



Leaves elongate: spikelets lanceolate to ovate, commonly the former, acute or 



acuminate. 

 Lower leaf-sheaths terete or but little flattened, not keeled. 



Stems finally branched : plants without long rootstocks or stolons. 

 Sheaths very pubescent. 



Spikelets lanceolate, 3 mm. long or less. 



Stems stout : panicle usually included at the base, its many 

 branches repeatedly divided and bearing numerous spikelets. 



1. P. capillare. 



Stems slender : panicle exserted, its few 

 branches but little divided and bear- 

 ing comparatively few spikelets. 

 Spikelets 2 mm. long, acute. 

 Spikelets 3 mm. long, acuminate. 

 Spikelets ovate, 5 mm. long or more. 

 Sheaths glabrous. 



Stems simple, from long stout rootstocks. 

 Lower leaf-sheaths much compressed, broad, keeled, often 



equitant. 

 Plants with no long rootstocks. 



Fourth scale of the spikelet sessile. 



Ligule naked : stems finally much branched. 

 Ligule ciliate : stems simple or nearly so. 

 Fourth scale of the spikelet distinctly stalked. 

 Plants with long scaly rootstocks. 



Leaves not elongate, except in nos. 11 and 12 : rosulate tufts 

 of leaves often present in the fall : spikelets oval to 

 obovate or globose, obtuse, or rarely acutish (acute 

 in no. 12). 



Middle leaf-blades of the main stem less than 1.5 cm. 

 broad, usually less than 1 cm., the base rounded 

 or truncate, rarely subcordate, sometimes nar- 

 rowed. 



Leaf-blades elongate, erect or nearly so, narrow, dis- 

 tinctly narrowed toward the base, especially 

 the lower ones. 

 Spikelets less than 3 mm. long, obtuse or 



acutish, pubescent. 



Spikelets 3-4 mm. long, acute, glabrous. 

 Leaf-blades not elongate, lanceolate, not manifestly 



narrowed toward the base. 



Stems, leaf-blades and sheaths glabrous, or the 

 latter two parts merely ciliate on the 

 margins. 

 Spikelets glabrous. 



Nodes of the stem naked. 

 Nodes of the stem densely barbed. 

 Spikelets pubescent. 

 Stems, leaf-blades, or sheaths, or all of them 



pubescent. 

 Spikelets 2.5 mm. long or less. 



Leaf-blades glabrous, or sometimes pubes- 

 cent beneath. 



Spikelets about 1.25 mm. long : stems 

 glabrous. 



11. P. linearifolium. 



12. P. depauperatum. 



13. P. dichotomum. 



14. P. microcarpon. 

 19. P. sphaerocarpon. 



Spikelets about 2.5 mm. long : stems 



puberulent. 

 Leaf-blades strongly pubescent beneath, 



usually also above. 

 Hairs on the lower surface long and 



stiff. 

 Hairs on the lower surface soft and 



copious. 



Spikelets exceeding 3 mm. in length. 

 Middle leaf-blades of the main stem 1.5 cm. wide, often 



3 cm., the base cordate and clasping. 

 Spikelets less than 3 mm. long. 



Spikelets about 1.5 mm. long : panicle oblong 



and dense : stems simple. 



Spikelets more than 2 mm. long : panicle ovoid 

 and open : stems branched. 



15. P. Lindheimeri. 

 22. P. Ashei. 



16. P. Huachucae. 



17. P. tennesseense. 



18. P. Scribnerianum. 



20. P. polyanthes. 



Leaf-sheaths glabrous. 



Leaf-sheaths papillose-hispid, especially 



short terminal ones on branches. 

 Spikelets 3 mm. long or more. 

 Nodes naked. 

 Nodes manifestly and copiously barbed. 



the 



21. P. commutatum. 



24. P. clandestinum. 



23. P. latifolium. 



25. P.Boscii. 



