6(5). Panicles open, the spikelets on slender pedicels 6. M. asperifolia. 



6. Panicles narrow, more or less condensed, the spikelets on short pedicels (7) 



7(6). Culms smooth, widely creeping, the blades fine, conspicuously recurved, 

 spreading 4. M. utilis. 



7. Culms nodulose-roughened, erect or decumbent at base, sometimes spreading 



but not widely creeping 5. M. Richardsonis. 



8(5). Hairs at base of floret copious, as long as the body of the lemma 



7. M. andina. 



8. Hairs at base of floret inconspicuous, not more than half as long as the lemma 



(9) 



9(8). Glumes with stiff scabrous awn-tips, much-exceeding the awnless lemma; 

 panicles terminal on the culm or leafy branches, compact inter- 

 rupted, bristly 8. M. racemosa. 



9. Glumes acuminate, sometimes awn-tipped but not stiff and exceeding the 



lemma; panicles terminal and axillary, numerous, not bristly (10) 



10(9). Culms glabrous below the nodes; panicles not compact, the branches 

 ascending; plants sprawling, top-heavy, the branchlets geniculate- 

 spreading 9. M. frondosa. 



10. Culms strigose below the nodes; panicles compact or (if not) the branches 



erect or nearly so; plants often bushy-branching but not sprawling 

 with geniculate branchlets (11) 



11(10). Panicles not compactly flowered; lemma with awn as much as 1 cm. 



long or more; some of the blades 1-1.5 dm. long or more 



10. M. sylvatica. 



11. Panicles compactly flowered or (if not) lemma awnless; blades commonly 



less than 1 dm. long but sometimes longer 11. M. mexicana. 



12(4). Culms decumbent and rooting at the nodes 12. M. Schreheri. 



12. Culms erect or spreading but not rooting at nodes 3. M. filiformis. 



1. Muhlenbergia minutissima (Steud.) Swall. Fig. 117. 



Tufted annual; culms 10-35 cm. long, 0.4-1 mm. thick, geniculately branched 

 near the base; ligule a hyaline soon lacerate scale about 2 mm. long, not auricled; 

 blades 3-10 cm. long, 1-2 mm. broad, usually flat, folded or involute on drying, 

 minutely pubescent; panicles 1-2 dm. long, 2-3 cm. broad, open and diffuse, the 

 numerous main branches often flexuous, ascending, much-branched secondarily; 

 glumes 0.6-1 mm. long, minutely pubescent (use strong lens); lemma 1.2-2 mm. 

 long, very finely pubescent, broadly elliptical, blunt or apically minutely bifid, awn- 

 less or with an awn to about 1 mm. long; palea about equaling lemma. M. texana 

 Buckl., M. sinuosa Swall. 



Rocky grassy slopes, border of marshes and wet canyon walls, in the Tex. 

 Trans-Pecos (Davis Mts.), rare, N. M. (Hitchcock) and Ariz. (Apache, Navajo, 

 Coconino, Yavapai, Gila and Pima cos.), late summer-fall; Mont, to Wash, and 

 s. to Mex. 



2. Muhlenbergia pectinata C. O. Goodd. 



Culms 1-2.5 dm. tall or long, erect to decumbent, sometimes rooting at the 

 lower nodes, freely branching, angular; sheath margins often ciliate; ligule erose 

 to ciliate, about 0.5 mm. long; blades flat to involute, 1-6 cm. long, 1-2 mm. 

 wide, pubescent or sparsely pilose; panicles numerous, narrow, 2-12 cm. long; 

 spikelets 3.5-4.5 mm. long; glumes abruptly acute to acuminate, commonly 

 aristate, 1.5-2 (-3) mm. long, the awn about half the entire length; lemma 3- to 

 5-nerved, scabrous to prominently ciliate on the lateral nerves, the callus appressed- 

 pubescent; awn 1-3 cm. long. 



246 



