AGROSTIDEAE 



55 



22. ARISTIDA L. 



Plants annual. 

 Plants perennial. 



Stems and branches of the panicle widely 

 spreading, straight and rigid. 

 Awns 3, all about the same length. 

 Awns apparently 1, the lateral ones very 

 short or wanting. 



Stems and panicles erect, or at most weakly 

 spreading. 



Empty glumes nearly the same length. 

 I'lant stout and strict, a foot high or 

 more, with short, straight pedicels; 

 empty glumes conspicuously awned. 

 Plant low and rather spreading, 10 inches 

 high or less, with slender though stiff 

 pedicels; empty glumes acuminate 

 but not awned. 

 Empty glumes very unequal in the length, 

 the lower one only about 1-2 as long as 

 the upper. 



Mature flowering glume not tapering up- 

 ward, the neck about the same diam- 

 eter as the base; second empty glume 

 considerably longer than the flower- 

 ing glume; the latter smooth; awns 

 very long, often 3 inches or more 

 Mature flowering glume tapering up- 

 wards into a slender neck; second 

 empty glume barely surpassing the 

 flowering or usually shorter, the lat- 

 ter scabrous; awns less than 2 inches 

 long usually (sometimes longer). 

 Spikelets small, 10 mm. long or less, 

 the awns never more than twice as 

 long, usually numerous. 

 Panicle strict, many flowered, and 



crowded, never spreading. 

 Panicle spreading at least at matur- 

 ity. 

 Pedicels weak and sinuous; awns 

 merely spreading; panicle 



spreading from the first. 

 Pedicels rigid, straight, ascending; 

 awns divergent at right angles 

 to the flowering glume; panicle 

 at first congested, opening at 

 last. 



Spikelets larger, 15 mm. long or more; 

 the awns usually more than twice 

 as long as the flowering glume. 

 Panicle simple or nearly so. 

 Panicle strict: spikelets numerous 

 and crowded, relatively small; 

 pedicels short, erect. 

 Panicle more lax; the pedicels long- 

 er: spikelets few. scattered, 15 

 mm. long. 

 Panicle compound, with numerous 

 large spikelets. 



Stems stout; panicle rigidly erect; 

 pedicels straight. 



1. A. Bromotdes, 



2. A. divaricata. 



3. A. schiediana. 



4. A. Arizonica. 



5. A. havardii. 



G. A. longiseta. 



7. A. vaseyu 



8. A. micrantha, 



9. A. n. sp. 



7. A. vaseyi. 



10. A. fendleriana. 



11. A. wrightii. 



