GRASS FAMILY 93 



Spikelets compressed, spreading. 5. A, arizonicum. 



Lemma a^vnless or with a very short erect awn ; empty glumes usually narrowly 

 lanceolate, acuminate. 

 Sheaths conspicuously pilose. 16. A. Palmeri. 



Sheaths glabrous or nearly so. 



Lemma glabrous or merely scabrous. 



Spikelets erect, nearly cyliiidric or sliglitly compressed. 



Spike elongate: empty glumes nearly equalling the spikelets. 



17. A. pseudorrpcns. 



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



18. A. riparium. 

 Spikelets much flattened, spreading. 10. A. ST7iithii. 



Lemma irom villous to hispidulous. 

 Lemma short-pubescent. 



Spikelets compressed, more or less spreading; lemma acuminate or 



strongly acute. 20, A. mollc. 



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

 Spike loose* elongate; lemma sparingly pubescent. 



21. A. lanceolatum. 



Spike dense and short; lemma densely pubescent. 



22. A. subrillosum. 

 Lemma long-villous. ' 23. A, dasystachvum. 



1. A. Scribneri Vasey. 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 glumes linear-lanceolate or subulate, 3-5-ncrvcd, smooth, long- 

 awned; lemma oblong-lanceoLate, 8-10 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.— N.M.— Ariz. Subalp.~AIp, Jl-Au. 



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

 slender; blades 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: 

 ^yash, — Alta. — Wyo.; Siberia. Submont, Jl-Au. 



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

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

 cm. long, often somewhat flexuose; spikelets 3-5-flowered; empty glumes oblance- 

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

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

 Colo. — Mont. Submont. My-Au. 



4. A. spicatum (Pursh) Scribn. & 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. A. divergens Nees. Bunch Guass. Dry rocky 

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



Je--Au. 



5. A. arizonicum Sciibn. & Smith. Tufted, but occasionally with long 

 stolons; stem 4-6 dm. high, minutely 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, 3-5-nerved; lemma 10-15 mm. long, acuminate, 

 scabrous; a\\'n about 2.5 mm. long. Mountains: Colo.— X.M.— Ariz.; n Mex. 

 Submont. — Subalp. Au-0. 



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

 dm. long, 2-4 mm. wide; spike 9-12 cm. long, dense, scarcely exserted; 



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

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

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

 Colo.— N.M. Mont. Au. 



7. A. Richardsoni (Trin.) Schrad. Stems smooth, 6-8 dna. 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. 



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