MANUAL OF THE GRASSES OF THE UNITED STATES 231 



Lemmas glabrous (sometimes pubescent in A. riparium). 

 Blades lax, flat. 



Glumes shorter than the spikelets; rachilla glabrous 2. A. repens. 



Glumes nearly as long as the spikelet; rachilla pubescent. 



4. A. PSEUDOREPENS. 



Blades firm, stiff, often involute. 



Spikelets much compressed, closely imbricate, the spike dense. 



3. A. PUNGENS. 

 Spikelets not much compressed, somewhat distant, the spike slender. 



8. A. RIPARIUM. 



Lemmas pubescent. 



Spike 6 to 12 cm. long; spikelets 1 to 1.5 cm. long; glumes 6 to 9 mm. long. 



6. A. DASYSTACHYUM. 



Spike as much as 25 cm. long; spikelets as much as 2.5 cm. long; glumes to 13 mm. 



long 7. A. ELMERI. 



lb. Plants without creeping rhizomes. 



Spikelets much compressed, crowded on the rachis 1. A. desertorum. 



Spikelets not much compressed nor divergent. 

 Spikelets awnless or awn-tipped only. 



Glumes 2 to 2.5 mm. wide, nearly as long as the spikelet; rachilla villous. 



Glumes with a broad subhy aline margin, unsymmetrical at the summit; lemmas 

 commonly pubescent; spike rarely more than 7 cm. long, the spikelets closely 



imbricate 14. A. latiglume. 



Glumes not thin-margined; lemmas glabrous; spike 10 to 25 cm. long, the spikelets 



mostly scarcely or slightly imbricate 13. A. trachycaulum. 



Glumes narrower, much shorter than the spikelet; rachilla scaberulous. 



Blades involute (rarely flat) 19. A. inerme. 



Blades fiat 21. A. parishii. 



Spikelets awned. 



Culms prostrate-spreading 17. A. scribneri. 



Culms erect (decumbent at base in A. pringlei). 

 Rachis finally disarticulating. 



Glumes narrow, 2-nerved; awns of lemmas spreading, out-curved or recurved. 



22. A. saxicola. 

 Glumes broader, with usually 3 to 5 distinct scabrous nerves; awn straight, 2 to 



5 cm. long 23. A. saundersii. 



Rachis continuous. 



Awn straight or nearly so. 



Spikelets about as long as the internodes of the rachis 21. A. parishii. 



Spikelets imbricate, longer than the internodes of the rachis. 



Lemmas coarsely pubescent 11. A. vulpinttm. 



Lemmas glabrous or scabrous toward summit only. 



12. A. SUBSECUNDUM. 



Awn divergent, when dry. 



Spikelets imbricate 15. A. bakeri. 



Spikelets distant. 



Spikelets 3 to 7 in a spike, about twice as long as the internode ; spike 4 to 



7 cm. long 16. A. pringlei. 



Spikelets mostly more than 7 in a spike, usually shorter than the internode; 

 spike mostly more than 8 cm. long. 



Spike 8 to 15 cm. long; blades 1 to 2 mm. wide 18. A. spicatum. 



Spike 15 to 30 cm. long; blades 4 to 6 mm. wide 20. A. arizonicum. 



1. Agropyron desertorum (Fisch.) 

 Schult. (Fig. 306.) Culms slender, 12 mm. long, 5- to 7-flowered, some- 

 erect or geniculate at base, in dense what spreading; glumes and lemmas 

 tufts, 25 to 100 cm. tall; sheaths gla- firm, glabrous to sparsely ciliate on 

 brous or the lower spreading-hirsute ; the keel, both abruptly narrowed into 

 blades 2 to 4 mm., occasionally to 5 an awn 2 to 3 mm. long, the lemma 

 mm. wide; spike 5 to 9 cm. long, 7 to about 6 mm. long, the awn commonly 

 11 mm. wide, somewhat bristly, the slightly bent to one side. % ("A. 

 short-jointed rachis pubescent; spike- cristatum" of Manual, ed. 1) — Grown 

 lets closely spaced on the rachis, 8 to in experiment stations and found here 



