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



3a. Mature lemma 2 to 3 mm long. Awn capillary, nexuous, about 5 cm 



l on g 32. S. TENUISSIMA. 



3b. Mature lemma at least 5 mm long. 



4a. Lemma densely appressed-villous with white hairs 3 to 4 mm long, 



rising above the summit in a pappuslike crown 5. S. cokonata. 



4b. Lemma often villous but the hairs not more than 1 mm long, or some- 

 times those at the summit as much as 2 mm long. 

 5a. Summit of mature lemma smooth, cylindric, whitish, forming a 

 ciliate crown 0.5 to 1 mm long (see also S. pulchra). 



3. S. LEUCOTRICHA. 



5b Summit of mature lemma not forming a crown. 



6a. Lemma 2-lobed at summit, the lobes extending into awns 2 to 



3 mm long on each side of the central awn 4. S. stillmanii. 



6b. Lemma not lobed at summit or only slightly so. 



7a. Awn plumose below, the hairs ascending or spreading (com- 

 pare S. pulchra, with appressed-hispid awn). 

 Sheaths pubescent. 



Awns once or obscurely twice-geniculate. _ 22. b. curvifolia. 

 Awns distinctly twice geniculate. 



Lemmas 6 to 7 mm long; glumes thin 17. S. elmeri. 



Lemmas 8 to 9 mm long; glumes firm.. 18. S. latiglume. 



Sheaths glabrous. 



Ligule 3 to 6 mm long 16. S. thurberiana. 



Ligule very short. 



Hairs on upper part of the lemma much longer than those 



below 21. S. CALIFORNICA. 



Hairs short all over the lemma 19. S. occidentals. 



7b. Awn scabrous or nearly glabrous, rarely appressed-hispid, not 

 plumose. 

 8a Lemma more than 7 mm (often 1 to 2 cm) long, glabrous or 

 sparsely pubescent above the callus, mostly cylindric (some- 

 what fusiform in S. pulchra). 

 Mature lemma pale or finally brownish, sparsely pubescent to 

 summit, mostly more than 1 cm long__ 10. S. comata. 

 Mature lemma dark. 



Lemma 8 to 10 mm long. 



Glumes 3-nerved. Summit of lemma hispidulous-ciliate, 

 the hairs erect, nearly 1 mm long; lemma somewhat 

 fusiform, pubescent in lines above the callus. 



11. S. PULCHRA. 



Glumes 5- to 9-nerved. 



Lemmas glabrous above the base, minutely roughened at 



apex; callus with fine sharp point. 8. S. avenacea. 



Lemmas sparsely pubescent to apex; callus rather 



blunt 12. S. PRINGLEI. 



Lemma 12 to 25 mm long, cylindric. 



Mature lemma glabrous above the callus. 



7. S. AVENACIOIDES. 



Mature lemma more or less pubescent above the callus. 



9. S. SPARTEA. 



8b. Lemma less than 7 mm long, or if as long as 7 to 8 mm, 

 distinctly pubescent on the upper part. 

 Panicle open, the branches spreading or ascending, naked at 

 base. . 



Panicle diffuse, the branches divergent, drooping; lemma 

 about 5 mm long; awn about 2 cm long. 



6. S. RICHARDSONI. 



Panicle open but not diffuse. 



Ligule 3 to 6 mm long; awn about 5 cm long, the terminal 



segment flexuous 13. S. eminens. 



Ligule 1 mm long or less; awn 2.5 to 4 cm long. 



14. S. LEPIDA 



Panicle narrow, the branches appressed. 



Hairs on lemma copious, at least at summit, 2 mm long. 

 Lemmas evenlv villous all over; summit with lobes 0.8 to 



1.5 mm long 20. S. lobata. 



Lemmas conspicuously villous above, less so below; sum- 

 mit not lobed or obscurely so. 



