286 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



12. AIRA L. Hairgrass. 



Erect perennial bunchgrasses with slender simple culms and shining few-flowered 

 spikelets, the florets awned from the back below the middle. 



Panicles long and narrow; blades filiform 1. A. elongata. 



Panicle open, commonly nearly or quite as wide as long; blades not fiUform. 



Blades firm, folded, mostly 2 to 4 mm. wide 2. A. caespitosa. 



Blades soft, flat, 5 to 10 mm. wide 3. A. atropurpurea. 



1. Aira elongata Hook. At low and middle altitudes, in meadows or on open 

 slopes. B. C. to Ariz, and Wyo. (Deschampsia elongata Monro.) — Plants 30 to 60 cm- 

 tall, the loose narrow panicle being one-fourth to one-third the entire height of the 

 plant; spikelets commonly purple-tinged; awns exceeding the glumes. 



2. Aira caespitosa L. Common at low altitudes, in meadows, on stream or lake 

 banks, or on open hillsides. Alaska to Calif., N. Mex., N. J., and Newf.; also in 

 Eur. and Asia. (Deschampsia caespitosa Beauv.) — Plants 20 to 60 cm. tall, often 

 forming dense cushions, the spreading leaves mostly crowded toward the base of the 

 culms; panicles with spreading capillary branches in distant fascicles; spikelets 

 from pale to piu-plish bronze; awns inconspicuous. 



3. Aira atropurpurea Wahl. At middle and high altitudes, in woods or on open 

 slopes. Alaska to Calif., Colo., N. H., and Greenl.; also in Eur. (Deschampsia atro- 

 purpurea Scheele.) — Plants 30 to 50 cm. tall, with abundant soft green foliage and 

 drooping panicles, the piirplish spikelets 5 mm. long, the bent awns about reaching 

 the apex of the glumes. 



13. TRISETUM Pers. 



Erect perennials resembling Aira, the spikelets as in that genus, but the lemmas 

 keeled, awned from the back above the middle (the awn obsolete in one species) and 

 2- toothed at the acute apex. 



Panicles loose, drooping or nodding; blades elongate, lax, 8 to 15 mm. wide. Awns 

 more than twice as long as the spikelet. 



Panicle branches capillary, drooping, 5 to 10 cm. long 1. T. cernuum. 



Panicle branches slender but rather stiffly ascending 2. T. canescens. 



Panicles mostly dense (if rather loose, the awns nearly obsolete), erect; blades rarely 

 over 5 mm. mde. 



Awns minute or obsolete 3. T. wolfii. 



Awns conspicuous 4. T. spicatum. 



1. Trisetum cernuum Trin. Frequent at middle altitudes. Alaska to Calif, and 

 Mont.— A woodland grass, often 1 meter tall, with drooping scabrous blades; panicle 

 branches spikelet-bearing toward the ends only; spikelets about 1 cm. long, excluding 

 the spreading awns; rachilla joints half as long as the florets. 



2. Trisetum canescens Buckl. At low and middle altitudes, in damp or rocky 

 woods. B. C. and Mont, to Calif. — A woodland grass resembling the preceding, but 

 the leaves softly pubescent, the panicle more densely flowered, the stiff er panicle 

 branches spikelet-bearing nearly to the base, the rachilla joints short, bringing the 

 florets close together in the spikelet. 



3. Trisetum wolfii Vasey. At low and middle altitudes, in meadows or moist 

 woods or on open slopes. Wash, to Calif., Colo., and Mont. (Graphephonim wolfii 

 Vasey.) — Plants tufted, 50 to 90 cm. tall, leafy, the panicles mostly dense but not 

 spikelike, the awns minute or obsolete. 



4. Trisetum spicatum (L.) Richt. Very common above timber line in meadows; 

 sometimes also at middle elevations. Alaska to Calif., N. Mex., N. H., and Greenl.- 

 also in Eur. and Asia. — Plants densely tufted, 15 to 50 cm. tall, the foliage relatively 

 scant and crowded toward the base, commonly grayish-velvety, the panicles dense^ 

 spikelike, the awns spreading. 



