POACEAE 



115 



Spikelets crowded, 4-6 on the short panicle-branches which are 



spikelet-bearins to the base or nearly so. 

 Spikelets not crowded, usually 1-3, or if more numerous the branches 

 of the panicle, or their divisions, with a long naked base. 

 Flowering scale not twisted at the summit. 



Second scale of the spikelet 1.5 cm. long or less, usually 

 equalling or slightly exceeding the flowering scale. 

 Panicle simple or nearly so; branches bearing 1 spikelet, 

 or the longer sometimes 2 spikelets : stems commonly 

 naked above. 

 Branches appressed, the longer, exclusive of the spike- 

 lets, usually 1 cm. long or less. 

 Branches spreading or ascending, sometimes flexuous, 

 the longer, exclusive of the spikelets, usually 1.5-3 

 cm. long. 

 Panicle compound ; branches bearing 2 or more spikelets : 

 stems usually leafy. 

 Stems stout : panicle branches straight. 

 Stems slender : panicle branches filiform, flexuous. 

 Second scale of the spikelet 12-15 mm. long, the awns 

 of the flowering scale cornmonly 3-4.5 cm. long. 

 Second scale of the spikelet usually less than 1 cm. 

 long, the awns of the flowering scale generally 

 2 cm. long or less, rarely longer. 

 Second scale of the spikelet 2 cm. long or more, from y^ again as 

 long as to nearly twice the length of the flowering scale. 

 Flowering scale twisted at the summit. 



Spikelets few and scattered : flowering scale without a long 

 beak, much shorter than the second scale, the awns inter- 

 lacingly coiled at the base. 

 Spikelets many and crowded : flowering scale with a long 

 beak, equalling or exceeding the second scale, the awns 

 not coiled at the base. 

 ** First scale a little shorter than or exceeding the second. 

 Flowering scale not twisted. 



Spikelets exceeding 2 cm. long : first scale 5-7-nerved. 



Spikelets less than 1.5 cm. long : first scale 1-3-nerved. 



Sheaths glabrous, or pubescent only at the apex. 



Leaves, at least the lower ones and those on the innova- 

 tions, with the base of the strongly involute blades 

 densely villous. 

 Leaves with the base of the flat blades at least not villous. 

 First scale of the spikelet 1-nerved. 



First scale glabrous : stems single or few in a tuft. 

 First scale hispidulous : stems densely tufted. 



First scale generally shorter than or equalling the 

 second. 

 Annual : flowering scale equalling or exceeding 

 at least the body of the second scale. 

 Flowei-ing scale 5^6 mm. long, its central awn 



usually 6-10 mm. long. 

 Flowering scale 7-9 mm. long, its central awn 

 exceeding 15 mm. in length. 

 Perennial : flowering scale manifestly shorter 

 than the second scale. 

 First scale usually exceeding the second. 

 First scale of the spikelet strongly 2-3-nerved. 

 Sheaths, at least the lower ones, densely woolly pubescent. 

 Flowering scale twisted above for the greater part of its length, 

 b. Panicle diffuse and open, the branches elongated and widely spread- 

 ing, with a long naked base. 

 B. Awns united at the base into a spiral column which is articulated to the scale. 

 Column conspicuous, 6 mm. long or more. 

 Column inconspicuous, 2 mm. long or less. 



7. A.fasciculata. 



8. A. Fendleriana. 



9. A. subuniflora. 



10. A. Wrightii. 



11. A. pxirptirea. 



12. A. micrantha. 



13. A. longiseta. 



14. A. gyrans. 



15. A. Reverchonii. 



16. A. oUgantha. 



17. A. stricta. 



18. A. condensata. 



19. A. gracilis. 



20. A. intermedia. 



21. A. Chapmaniana. 



22. A. purptirascens. 



23. A. palustris. 



24. A. lanosa. 



25. A. spiciformis. 



26. A. patula. 



27. A. fubcrculosa. 



28. A. desmantha. 



1. Aristida dichotoma Michx. Stems densely tufted, slender, 2-6 dm. tall, finally 

 1)ranching: leaf-blades erect, 2-9 cm. long, 1.5 mm. wide or less, sparingly pilose above 

 toward tlie base: panicle 3.5-7 cm. long, the branches short or erect : spikelets 7-9 mm. 

 long, the 2 outer scales about equal in length, or the first a little the shorter, usually awn- 

 pointed, the flowering scale 5-7 mm. long, the lateral awns very short, erect, the central 

 awn spreading, spiral at the base, the straight portion 2-5 mm. long, rarely longer. 



In dry sandy soil, Maine to Ontario, Missouri and the Indian Territory, Florida and Texas. Sum- 

 mer and fall. Poverty Gr.\ss. 



2. Aristida Curtissil (A. Gray) Nash. Stems tufted, 2-5 dm. tall, branching : leaf- 

 blades 4-16 cm. long, 1-2 mm. wdde, sometimes sparsely pilose above near the base : pani- 

 cle 5-9 cm. long, the branches erect: spikelets generally 10-12 mm. long, rarely longer, 

 the first scale much shorter than the second which usually about equals the flowering one, 

 rarely somewhat exceeding it, the flowering scale 7-11 mm. long, the lateral awns very 

 short, 1-2 mm. long, straight and erect, usually less than i as long as the central awn 

 which has the straight portion 5-8 mm. long. 



In dry soil, Missouri and Kansas to the Indian Territory ; also in Virginia. Fall. 



