MANUAL OF THE GRASSES OF THE UNITED STATES 369 



2.5 to 3 mm long, the glumes about half as long, awn-tipped, the first 

 rather narrow, acuminate, the second broader, 3-nerved, sharply 3- 

 toothed, rarely entire or erose only ; 

 lemma pubescent on the lower 

 half, tapering to ana wned tip. % 

 — Open sandy or rocky soil, 2,000 

 to 3,000 m 'altitude, Wyoming, 

 Colorado, and New Mexico. 



18. Muhlenbergia arizonica 

 Scribn. (Fig. 757.) Perennial, 

 in close tufts; culms slender, 

 erect or decumbent at base, 15 

 to 40 cm tall; sheaths keeled; 

 ligule thin, 1 to 2 mm long, 

 decurrent; blades flat or folded, 

 mostly less than 5 cm long, 1 to 

 2 mm wide, the margins and mid- 

 nerve white, cartilaginous; pan- 

 icle open, 5 to 12 cm long, 4 to 

 8 cm wide, the branches capillary, 

 compound ; spikelets long-pedicel- 

 late, about 3 mm long, the glumes 

 about one third as long, ovate, 

 subacute ; lemma narrowly lanceo- 

 late, minutely pubescent along 

 the midnerve and margins below, 

 the awn about 1 mm long, from a 

 minutely notched apex. % — 

 Stony hills, southern Arizona and 

 northwestern Mexico. 



19. Muhlenbergia dumosa 

 Scribn. (Fig. 758.) Perennial, 

 with short, stout creeping scaly 

 rhizomes; culms robust, solid, 

 thick, and scaly at base (here as 

 much as 6 mm thick), the main 

 culm erect or leaning, 1 to 3 m 

 tall, the lower part clothed with 

 bladeless sheaths, freely branching 

 at the middle and upper nodes, 

 the branches numerous, fascicled, 

 spreading, decompound, the ultimate branchlets filiform; blades flat or 

 soon involute, smooth, those of the branches mostly less than 5 cm 



long and 1 mm wide; panicles numerous on the 

 branches, commonly exceeded by the leaves, 1 

 to 3 cm long, narrow, somewhat flexuous; spike- 

 lets, excluding the awn, about 3 mm long, the 

 glumes scarcely half as long, thin, pale with a 

 green midnerve, usually minutely awn-tipped; 

 lemma narrow, pubescent about the base and 

 margin, pale with green nerves, the awn from the 

 slightly notched apex, flexuous, 3 to 5 mm long. % — Canyons and 

 valley flats, southern Arizona to Jalisco Mexico. Has the aspect of a 

 small bamboo. 



Figure 752. — Muhlenbergia uniflora. Plant, 

 X 1; glumes and floret, X 10. (Chamber- 

 lain 147, Maine.) 



Figure 753.— Distribution of 

 Muhlenbergia uniflora. 



