GRASS FAr^IILY 93 



Spikelets compressed, spreading. 5. A. arizonicum. 



Lemma awnless or with a verj- short erect awn; empty glumes usually narrowly 

 lanceolate, acuminate. 

 Sheaths conspicuously pilose. 16. A. Palmeri. 



Sheaths glabrous or nearly so. 



Lenuna glabrous or nierelj- scabrous. 



Spikelets erect, nearly cylindric or slightly compressed. 



Spike elongate: empty glumes nearly equalling the spikelets. 



17. A. pseudorrpens. 

 Spike short; empty glumes about half as long as the spikelets. 



18. A. riparium. 

 Spikelets much flattened, spreading. 19. A. Smithii. 



Lemma from villous to hispidulous. 

 Lemma short-pubescent. 



Spikelets compressed, more or less spreading; lemma acuminate or 



strongly acute. 20. A. moUe. 



Spikelets terete or nearly so, erect; lemma obtuse or acutish. 

 Spike loose, elongate; lemma spaiingly pubescent. 



21. A. lanceolatum. 

 Spike dense and short; lemma densely pubescent. 



22. A. subvillosum. 

 Lemma long-villous. 23. A. dasystachyum. 



1. A. Scribneri \'asev. Densely tufted perennial; stems decumbent and 

 geniculate at the base, 2-5 dm. high; leaf-blades short, 3-10 cm. long, 2-4 mm. 

 wide, rigid, attenuate-pointed; spike 5-7 cm. long, flexuous: spikelets 3-6- 

 flowered; empty gkmies linear-lanceolate or subulate, 3-o-nerved, smooth, long- 

 awned; lemma oblong-lanceolate, S-10 mm. long, smooth, 5-nerved; awn diverg- 

 ent, scabrous, 1.5-2.5 cm. long. This species connects the genus with Sitanion. 

 High moimtains: Mont. — X.^I. — Ariz. Subalp. — Alp. Jl-Au. 



2. A. Gmelini (Griseb.) Scribn. <t Smith. Stems 6-12 dm. high, glabrous, 

 slender; blatles of stem-leaves 12-30 cm. long, flat or involute; those of the basal 

 leaves 3-7 cm. long, 4-6 mm. wide; spike slender, 1-2.5 dm. long; spikelets 10- 

 20, 6-9 mm. long, 7-9-flowered ; empty glumes unequal, 10-14 mm. long, oblong- 

 lanceolate, acuminate or short-awned; lemma oblong-lanceolate, acuminate, 

 10-12 mm. long; awn scabrous, 15-30 mm. long, at last divergent. Hillsides: 

 Wash. — Alta. — -Wyo.; Siberia. Submont. Jl-Au. 



3. A. Vaseyi Scribn. <k Smith. Stem erect, 3-5 dm. high, wiry, glabrous; 

 leaf-blades 3-15 cm. long, 1-2 mm. wide, usually involute; spike slender, 5-10 

 cm. long, often somewhat iflexuose; spikelets 3-5-flowered; empU- glmnes oblance- 

 olate or oblong, acute or acuminate, 6-8 mm. long; lemma S mm. long, lanceo- 

 late, acute; awn 8-10 mm. long. Hills and moimtain sides: Wash. — Ore." — 

 Colo. — Mont. Submont. My-Au. 



4. A. spicatum (Pursh,) Scribn. k Smith. Stem 3-10 dm. high, glabrous; 

 leaf-blades 5-20 cm. long, 1-2 mm. wide, involute or rarely flat; spikes 8-20 cm. 

 long; spikelets 3-6-flowered, flattened; lemma 8-10 mm. long, scabrous above; 

 awn .stout, 12-25 mm. long. ^4. divergens Xees. Buxch Grass. Dry rocky 

 hills and bench-lands: B.C. — Calif. — Ariz. — Colo. — Mont. Plain — Submont. 

 Jt^Au 



5. A. arizonicum Sciibn. k Smith. Tufted, but occasionaU}- with long 

 stolons; stem 4-6 dm. high, minuteh* scabrous below; leaf-blades 1-3.5 dm. 

 long, 4-6 mm. wide; spike 7-20 cm. long, usually nodding: spikelets 7-14, distant, 

 5-7-flowered, 2-3.5 cm. long, 3-o-nerved; lemma 10-15 mm. long, acuminate, 

 scabrous; awn about 2.5 mm. long. Mountains: Colo. — X.M. — Ariz.;n^Iex. 

 Submont. — Subalp. Au-0. 



6. A. Bakeri E. Nels. Stem smooth, 3-5 dm. high; leaf-blades rigid, flat, 

 1-3 dm. long, 2-4 mm. wide; spike 9-12 cm. long, dense, scarceh* exserted; 

 spikelets about 5-flowered, 15-19 mm. long; empty glumes 11-12 mm. long, 

 scarious-margined, abrupth* acuminate, short awned; lemma scabrous or nearly 

 smooth, about 12 mm. long, attenuate; awn 1-3.5 cm. long. High moimtains: 

 Colo.— X.M. Mont. Au. 



7. A. Richardsoni (Trin.) Schrad. Stems smooth, 6-8 dm. high; leaf- 

 blades 8-20 cm. long, 2-6 mm. wide, scabrous, flat, often with involute tips; 

 spikes 7-10 cm. long, one-sided; spikelets 3-4-flowered; empty glume 12-16 mm. 



