178 



GRAMINEAE. 



Vol. I. 



33. ARISTIDA L. Sp. PL 82. 1753. 



Grasses varying greatly in habit and inflorescence. Leaf-blades narrow, often involute- 

 setaceous. Spikelets narrow, i-flowered. Scales 3, narrow, the two outer carinate; the third 

 rigid and convolute, bearing three awns occasionally united at the base, the lateral awns 

 rarely wanting or reduced to rudiments. Palet 2-nerved. Stamens 3. Styles distinct. 

 Stigmas plumose. Grain free, tightly enclosed in the scale. [Latin, from arista, an awn.] 



About 120 species, in the warmer regions of both hemispheres. The English name Three- 

 awned Grass is applied to all the species. Type species : Aristida adscensionis L. 



Awns not articulated to the scale. 

 Central awn coiled at the base. 



First scale usually equalling or sometimes slightly shorter than the second scale, which is 



commonly 3 I A"—4 I A" long. 1. A. dichotoma. 



First scale much shorter than the second (often but little more than yi as long), which 

 is s"-8" long. 

 Lateral awns short, straight and erect, j£"-i" long, the central awn usually more than 



five times their length, its straight portion 2 yi "-4" long. 2. A. Curtissii. 



Lateral awns more or less spreading, usually a little spiral at the base, the central awn 

 from yi again tc twice their lenth, its straight portion s"-8" long. 3. A. basiramea. 

 Central awn not coiled at the base. 



Panicle narrow, linear to oblong, branches short (or long in no. 13), erect or ascending. 

 Central awns and sometimes the lateral ones also stronlgy reflexed, the bend semicircular. 



f 4. A. ramosissima. 



Central awn from erect to spreading with no such bend at the base. 

 First scale much shorter than the second, usually about yi as long. 



Spikelets crowded, 4-6 on the short branches, which are spikelet-bearing to the 



base or nearly so. 5. A. fasciculata. 



Spikelets not crowded, usually 1-3 on branches naked at the base. 



Second scale of spikelet 8" long or less, equalling or exceeding flowering scale. 

 Panicle simple or nearly so, its branches bearing 1 spikelet ; culms com- 

 monly naked above. 6. A. Fendleriana. 

 Panicle compound, its branches bearing 2 or more spikelets; culms usually 

 leafy. 7. A. Wrightii. 

 Second scale of the spikelet 10" long or more, iyi-2 times as long as the 

 flowering scale. 8. A. longiseta. 

 First scale from a little shorter than to exceeding the second. 



Spikelets exceeding 10" long; first scale 5-7-nerved. 9. A. oligantha. 



Spikelets less than 8" long; first scale- 1-3-nerved. 

 Leaf-sheaths glabrous or sparsely pubescent. 



First scale generally shorter than or equalling the second. 

 Flowering scale 2yi"-3" long, its central awn usually 3"-5" 



10. A. „ 

 Flowering scale zyi"-\yi" long, its central awn exceeding 7" in length. 



11. A. intermedia. 

 First scale exceeding the second. 



Leaf-sheaths, at least the lower ones, densely wooly. 

 Panicle diffuse and open, the branches very long and widely spreading. 

 Awns articulated to the scale, united at the base into a spiral column. 

 Column conspicuous, 3" long or more. 

 Column inconspicuous, 1" long or less. 



long. 

 gracilis. 



12. A. purpurascens. 



13. A. lanosa. 



14. A. divaricata. 



IS. 



16. 



A. tuberculosa. 

 A. desmantha. 



i. Aristida dichotoma Michx. Poverty-grass. 

 Fig. 423. 



Aristida- dichotoma Michx. Fl. Bor. Am. 1 : 41. 1803. 



Culms 6'-2° tall, erect, slender, dichotomously 

 branched, -smooth or roughened. Sheaths much shorter 

 than the internodes, loose, smooth and glabrous ; ligule 

 very short, ciliate; blades 1-3' long, less than 1" wide, 

 involute, acuminate, usually scabrous ; spike-like racemes 

 or panicles 2-5-' long, slender; spikelets about 3" long; 

 outer scales nearly equal or the lower somewhat shorter, 

 usually awn-pointed ; third scale shorter than the second, 

 the middle awn horizontal, coiled at base, the terminal 

 straight portion 2"-$" long, the lateral awns 1" long 

 or less, erect 



Dry sandy soil, Maine to Nebraska, south to Georgia and 

 Texas. Aug.-Sept. 



