70 



POACEAE 



Spikelets glabrous : 



2 mm. long : leaves scattered along the stem. 

 1.5 mm. long : leaves crowded at tiie 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 



hrst 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 Iwng 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 paiirs. 

 ♦Stems tufted. 



tSpikelets 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, 3^ 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. ciUati/olium. 



8. P. Kentuckiense. 



9. P. longepeduncuMum. 



10. P. Eggertii. 



11. P. rigid i folium. 



12. P. epile. 



13. P. elatum. 



14. P. lati/vlium. 



15. P. gracillimum. 



16. P. pubescens. 



18. P. st'taceum. 



19. P. villosissimum. 



17. P. Muhlevbergii. 



20. P. dasyphyllum. 



21. P. scrobicidatum. 



22. P. laeve. 



23. P. angustifolium. 



24. P. australe. 



25. P. longipilum. 



26. P. praelongum. 



27. P. circutare. 



28. P. Simpsonii. 



29. P. lUodgettii. 



30. P. Hallii. 



31. P. laeinglumis^ 



32. P. gemimim. 



33. P. Boiirianum.. 



34. P. plicatidnm. 



35. P. difforme. 



36. P. aliissimum. 



