312 OHIO BIOLOGICAL SURVEY 



14. Outer empty glume V 3 as long as the spikelet, short acute. P. scribnerianum. 



14. Outer empty glume y 2 as long as the spikelet, long acuminate. 



P. xanthophysum. 



15. Stem simple or with basal branches only. 16 



15. Stem at length fasciately branched. 22 



16. Hairs on the leaf sheath almost y$ in. long or longer, spreading, usually 

 dense. . P- linear {folium. 



16. No hairs on the leaf sheath, or with hairs less than tV in. long, sometimes 

 ciliate on the margin. 17 



17. Leaf blade i% in. or less wide, usually 18 or more times as long as wide; 

 spikelets usually glabrous. 18 



17. Leaf-blade usually much more than *4 m - wide, never more than 8 times 

 longer than wide ; spikelets more or less pubescent 20. 



18. Leaves much elongated; often 6 to 10 in. long, attenuate at the base. 



P. werneri. 



18. Leaves not elongated ; generally less than V/ 2 in. long, not attenuate at the 

 base, spikelet less than Y% in. long. P. bickiiellii. 



19. Spikelets roundish, not over tV in. long. 20 



19. Spikelets oblong-elliptic or elliptic, usually tV in. or more long. 21 



20. Nodes pubescent with appressed hairs, base of the leaves ciliate, panicle nearly 

 as wide as long. P. sphaerocarpon. 



20. Nodes glabrous, base of the leaves not ciliate; panicle not more than V> as 

 wide as long. P. polyanthes. 



21. Stems pubescent. P. tsugetorum. 



21. Stems glabrous. P. boreale. 



22. Spikelets glabrous. 23 



22. Spikelets pubescent. 24 



23. Nodes densely bearded. P. microcarpon. 



23. Nodes not bearded. P. dichotomum. 



24. Ligule at the top of the leaf sheath minute or absent. 25 



24. Ligule present. 26 



25. Nodes of the main stem glabrous or with a few hairs. P. boreale. 



25. Nodes of the main stem pubescent. P. ashei. 



26. Upper sheaths glabrous, ciliate on the margin. P. liiidheimeri. 



26. All of the sheaths pubescent. 27 



27. Upper surface of the leaves glabrous, except for a few long hairs near the 

 base. P. tsugetorum. 



27. Upper surface of the leaves pilose. 28 



28. Outer empty glume acute; spikelet tV in. long, pubescence on the sheath more 

 than i$ in. long. P. villosissimum. 



28. Outer empty glume blunt; spikelet less than tV in. long; pubescence on the 

 sheaths not so dense and less than tV in .long. 29 



29. Upper surface of the leaf-blade long-pilose; plants yellowish-green. 



P. huachucae. 



29. Upper surface of the leaf-blade long appressed pubescent. P. implicatum. 



30. Spikelet )/% in. or more long. 32 



30. Spikelet less than % in. long. 31 



3L Spikelet less than & in. long. - P. polyanthes. 



31. Spikelet more than ^ in. long. P. commutatum. 



32. Leaf sheaths mostly papillose-hispid.; nodes glabrous or short pubescent. 



P. eland es tin u in. 



32. Leaf-sheaths glabrous or soft-pubescent. 33 



33. Nodes glabrous. P. latifoliiuii. 

 :;.'!. At least the lower nodes pubescent or bearded. [14 



34. Panicle narrow, its brandies appressed, rarely a little spreading; upper nodes 

 at least not bearded. P. xanthophysum. 



34. Panicle open, ils branches spreading; the nodes appressed-pubescent. P. boseii. 



