70 



POACEAE 



Spikelets glabrous : 



2 mm. long : leaves scattered along the stem. 

 1.5 mm. 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; spikelets 



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 lng 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 3 ; 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. 



fSpikelets rounded or obtuse at the apex, not ciliate on the mar- 

 gins. 



gSpikelets convex on one side. 

 Spikelets 3 mm. long or less. 

 Spikelets singly disposed. 



Spikelets oval, % 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 % 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 



spreading glandular-tipped hairs. 

 Spikelets elliptic, 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 flowering 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. 



7. P. ciliatifolium. 



8. P. Kentuckiense. 



9. P. longepedunculatum. 



10. P. Eggertii. 



11. P. ngidifolium. 



12. P. epile. 



13. P. elatum. 



14. P. lattfoUum. 



15. P. gracillimum. 



16. P. pubescent. 



18. P. setaceum. 



19. P. villosissimutn. 



17. P. Muhtenbergii. 



20. P. dasyphyUum. 



21. P. scrobiculaturn. 



22. P. laeve. 



23. P. angustifolium. 



24. P. australe. 



25. P. longipilum. 



26. P. praelongum. 



27. P. circulare. 



28. P. Simpsonii. 



29. P. Blodgettii. 



30. P. Hattii. 



31. P. laeviglumis. 



32. P. geminum. 



33. P. Boscianum. 



34. P. plicatulum. 



35. P. difforme. 



36. P. altissimuin. 



