POACEAE 1 1 7 



11. Aristida purpurea Nutt. Stems tufted, 2-4 dm. tall, slender, simple, leafy : 

 leaf-blades involute, at least when dry, often curved, those on tlie stem 2-5, 4-12 cm. 

 long : panicle 1-2 dm. long, its branches spreading or ascending, filiform, flexuous, often 

 with a long naked l)ase : spikelets 12-15 mm. long, the 2 outer scales l-nerved, frequently 

 awned, the first about \ as long as the second, the flowering scale about 1 cm. long, a little 

 flhorter than the second scale, the awns ascending, the central one about 3-5 cm. long, 

 the lateral awns a little shorter. 



In dry sandy soil, Arkansas and Louisiana, to New Mexico. Spring and summer. 



12. Aristida micrdntha ( Vasey) Nash. Stems tufted, 2-4 dm. tall, slender, simple : 

 leaf-blades 4-15 cm. long, involute, at least when dry : panicle 8-12 cm. long, its branches 

 filiform, flexuous, spreading or ascending : spikelets 2-4 on the longer branches, the 2 

 outer scales l-nerved, the second one 8-10 mm. long, the flowering scale 6-8 mm. long, the 

 awns ascending or nearly erect, the central awn 1.5-2 cm. long, rarely longer, the lateral 

 awns a little shorter. 



In dry soil, Texas. Summer. 



13. Aristida longis^ta Steud. Stems tufted, 2-4 dm. tall, simple : leaf-blades 3-10 

 cm. long, involute, at least when dry : panicle 1-2 dm. long, its branches usually ascend- 

 ing, bearing generally 1 spikelet, or in the longer branches sometimes 2 spikelets : spike- 

 lets 2-2.5 cm. long, the 2 outer .scales l-nerved, tlie firet one about j as long as the second, 

 the flowering scale 12-16 mm. long, occasionally a little shorter, from a little over J f as 

 long as the .second scale, the awns ascending, the central one 6-11 cm. long, the lateral ones 

 equalling it or a little sliorter. 



In dry sandy soil, Montana and Washington to Nebraska, Texas and Mexico. Summer and fall. 



14. Aristida gyrans Chapm. Stems 3-4 dm. tall, slender, simple : leaf-blades 

 6-12 cm. long, involute, about 0.5 mm. in diameter : panicle about 12 cm. long, slender, 

 its few branches short and appressed : spikelets 10-11 mm. long, the 2 outer scales l-nerved, 

 the first one shorter than the second, the flowering scale about 6 mm. long, including the 

 1.5 mm. long callus, the apex a little twisted, the awns ascending, loosely twisted together 

 at the base, the central awn about 12 mm. long, the lateral ones a little shorter. 



In sand. Keys of Caximbas Bay, southern Florida ; also in Cuba. Summer and fall. 



15. Aristida Reverchonii ^'asey. Stems tufted, 2-4 dm. tall, simple : leaf-blades 

 2-12 cm. long, involute, about 0.5 mm. in diameter : panicle 1-1.5 dm. long, its Itranches 

 usually short and appressed, rarely long and somewhat spreading : spikelets on short pedi- 

 cels, the 2 outer scales l-nerved, tlie first one much sliorter than the second which is 8-10 

 mm. long, the flowering scale 9-11 mm. long, usually hispidulous, with a long slender 

 more or less twisted summit, a little exceeding the second scale, the awns ascending, the 

 central one 1.5-2.5 cm. long, the lateral ones a little shorter. 



In dry soil, the Indian Territory and Texas. Spring and summer. 



16. Aristida oligdntha Michx. Stems tufted, 2-6 dm. tall, branching : leaf-sheaths 

 shorter than the internodes, smooth and glabrous ; blades 0.5-2 dm. long, 1-2 mm. wide : 

 panicle 1-2 dm. long, simple, its branches very short and bearing a single spreading spike- 

 let : spikelets 2-3 cm. long, the 2 outer scales usually awned, the first 5-7 -nerved, from a 

 little shorter than tlie second to a little exceeding it, 1.5-2 cm. long, the awns ascending, 

 tlie central one 3.5-7 cm. long, the lateral ones a little shorter. 



In dry usually sterile soil. New Jersey to Nebraska, Mississippi and Texas. Summer and fall. 



17. Aristida striata Michx. Stems densely tufted, 5-10 dm. tall, simple : leaf- 

 sheaths, the lower ones and especially those on the innovations, villous at the apex ; blades 

 involute, even when fresh, 0.5-3 dm. long, about 0.7 mm. in diameter, the lower ones and 

 those on the innovations densely villous at the base : panicle 1-3 dm. long, the short ap- 

 pressed branches in alternate fascicles of 2 or 3 : spikelets 10-11 mm. long, the 2 outer 

 scales l-nerved, usually awn-pointed, the first shorter than the second, the flowering scale 

 7-9 mm. long, glabrous or sparingly hispidulous toward the summit, the awns more or less 

 spreading, the central one 11-17 mm. long, the lateral ones from | to nearly as long. 



In dry sandy soil, Virginia (according to S. Watson) to Florida. Spring to fall. 



18. Aristida condeusata Chapm. Stems single or few in a cluster, 6-10 dm. tall, 

 simple : leaf-sheaths confined to the lower part of the stem, overlapping, glabrous or spar- 

 ingly pubescent ; blades 2-3 dm. long, flat when fresh, 2-3 mm. wide at the base from 

 which they gradually taper to a long slender acumination : panicles 2-5.5 dm. long, usually 

 densely spikelet-bearing, its branches erect or nearly so, the longer from 3-13 dm. long, 

 the spikelets crowded and overlapping: spikelets 8.5-10 mm. long, the 2 outer scales 

 l-nerved, glabrous, the first equalling or very little shorter than the second, the flowering 

 scale about 7 mm. long including the 1 mm. long and densely pilose callus, glabrous, the 

 awns spreading, the central one 10-14 mm. long, the lateral ones from f as long as to 

 nearly equalling it. [.4. Cnmbsil Scribn. ABall.] 



In dry sandy soil, Florida. Fall. 



