326 MISC. PUBLICATION 200, U. S. DEPT. OF AGRICULTURE 



Panicle open, the branches ascending, no long stolons developed. 

 Culms producing rather stout creeping leafy stolons. 9. A. nigra. 

 Culms decumbent at base; rhizomes wanting. 7. A. stolonifera. 



Culms erect; rhizomes present 10. A. alba. 



lb. Palea obsolete, or a minute nerveless scale (in A. exarata and A. californica 

 as much as 0.5 mm long or more). 

 3a. Plants annual; lemma with a slender awn 5 to 10 mm long. 



Awn flexuous; Southeastern States 15. A. elliottiana. 



Awn straight; Pacific coast. 



Spikelets 5 to 6 mm long; lemma awned from the middle — 



13. A. HENDERSONII. 



Spikelets about 1.5 mm long; lemma awned below the tip 



14. A. EXIGUA. 

 3b. Plants perennial; lemma awned or awnless, the awn when present not 

 much exserted. 

 4a. Plants spreading by creeping rhizomes (those of A. lepida short). 



Hairs at base of lemma 1 to 2 mm long 16. A. hallii. 



Hairs at base of lemma minute or wanting. 



Rhizomes short; alpine tufted plants 17. A. lepida. 



Rhizomes long and slender. 



Panicle spikelike 18. A. pallens. 



Panicle open 19. A. diegoensis. 



4b. Plants without rhizomes, stolons sometimes developed. 



5a. Panicle narrow, contracted, at least some of the lower branches 



spikelet-bearing from near the base. 



Culms slender, in dense tufts with numerous basal leaves; blades not 



more than 5 cm long, less than 2 mm wide; panicles seldom more 



than 5 mm wide. 



Blades involute; culms spreading; panicles strict — 20. A. blasdalei. 



Blades flat; culms erect; panicles not strict 21. A. rossae. 



Culms stouter, not in tufts with dense basal foliage; blades or some of 



them at least 8 to 10 cm long and 4 to 5 mm wide, commonly much 



larger. 



Panicle from loose to dense, if dense, in glomerules or interrupted; 



glumes, except the keel, smooth to scaberulous; palea less than 



one fourth as long as the lemma 22. A. exarata. 



Panicle dense and spikelike; glumes very scabrous; palea one fourth 



to one third as long as the lemma 23. A. californica. 



5b. Panicle open, sometimes diffusely spreading; lower branches not 

 spikelet-bearing at the base. 

 Awn attached near the base of the lemma; panicle diffuse. 



24. A. howellii. 

 Awn when present attached about the middle of the lemma or above. 



Panicles very diffu.se, the scabrous capillary branches branching 

 toward the end or (in A. hiemalis var. geminata) above the middle. 



25. A. hiemalis. 

 Panicles open but not diffuse, the branches branching at or below the 



middle. 

 Lemmas awnless (occasional plants with awned lemmas; see also 

 A. baker i). 

 Spikelets about 1.5 mm long; plants of high altitudes, delicate, 



10 to 30 cm tall 26. A. idahoensis. 



Spikelets 2 to 3 mm long; more robust plants of low and medium 

 altitudes. 

 Panicles rather lax, sometimes delicate and divaricately 

 spreading; blades flat, as much as 6 mm wide; eastern 



United States 28. A. perennans. 



Panicles rather stiff, the branches whorled and rather stiffly 



ascending; Pacific coast 29. A. oregonensis. 



Lemmas awned. 



Spikelets about 2 mm long; introduced 30. A. canina. 



Spikelets 2.5 to 3 mm long; native. 



Branches of panicle nearly smooth. Foliage mostly basal. 



31. A. borealis. 

 Branches of panicle scabrous. 



Awn short and straight 27. A. bakeri. 



Awn geniculate, exserted 32. A. longiligula. 



