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



Section 3. Chaetaria 



la. Central awn spirally coiled at the base, the lateral straight. Plants annual. 

 (Group Dichotomae.) 

 Lateral awns half to two-thirds as long as the central, somewhat spreading. 



8. A. BASIRAMEA. 



Lateral awns much shorter than the central, 1 to 3 mm long, erect. 



Glumes nearly equal, 6 to 8 mm long; lemma sparsely appressed-pilose, 5 to 



6 mm long 9. A. dichotoma. 



Glumes unequal, the second longer, about 1 cm long; lemma glabrous except 

 the keel, scabrous toward the apex, about 1 cm long. 10. A. curtissii. 

 lb. Central awn not spirally coiled (in a few species all the awns loosely con- 

 torted in the lower part) . 

 2a. Plants annual. (Group Adscensiones.) 



Awns mostly 4 to 7 cm long, about equal, divergent. _ 11. A. oligantha. 

 Awns mostly less than 2 cm long, often unequal. 



Central awn with a semicircular bend at base, spreading or reflexed. 

 Lateral awns much reduced; lemma about 2 cm long. 



12. A. RAMOSISSIMA. 



Lateral awns one-third to half as long as the central; lemma 4 to 5 mm 



long 13. A. LONGESPICA. 



Central awn not sharply curved, the awns about equally divergent. 

 Glumes unequal; awns flat at base, 10 to 15 mm long. 



14. A. ADSCENSIONIS. 



Glumes about equal; awns terete, 15 to 20 mm long. 



15. A. INTERMEDIA. 



2b. Plants perennial. 



3a. Panicle open, the branches spreading (in A. pansa ascending), naked 

 at base. (Group Divaricatae.) 

 Panicle branches stiffly and abruptly spreading or reflexed at base. 



Branchlets divaricate and implicate 16. A. barbata. 



Branchlets appressed. 



Summit of lemma narrowed into a twisted neck 2 to 5 mm long. 



17. A. DIVARICATA. 



Summit of lemma somewhat narrowed but not twisted. 



18. A. HAMULOSA. 



Panicle branches drooping or ascending, not abruptly spreading at base. 

 Lateral awns one-fourth to half as long as the central one. 



19. A. PATULA. 



Lateral awns about as long as the central, at least more than half as 



long 20. A. pansa. 



b. Panicle narrow, the branches ascending or appressed (branches some- 

 times somewhat spreading in A. parishii and A. purpurea). 

 Column 1 cm or more long, twisted; glumes awned. 21. A. spiciformis. 

 Column less than 1 cm long. 



Creeping rhizomes present. Glumes unequal, awned; awns loosely 

 twisted at base, the central a little longer, 18 to 24 mm long. 



31. A. RHIZOMOPHORA. 



Creeping rhizomes wanting (sometimes short ones in A. stricta). 



4a. First glume about half as long as the second (as much as two-thirds 

 as long in A. glauca). (Group Purpureae.) 

 Lemma tapering into a slender somewhat twisted beak 5 to 6 mm 

 long; awns 1.5 to 2.5 cm long, widely spreading. 



22. A. GLAUCA. 

 Lemma beakless or only short-beaked. 



Branches of the rather loose and nodding panicle slender and 

 flexuous (see also A. longiseta var. rariflora). 

 Lemma about 1 cm long; awns 3 to 5 cm long. 



23. A. purpurea. 

 Lemma 7 to 8 mm long; awns about 2 cm long. 



24. A. roemeriana. 

 Branches of the erect panicle stiff and appressed, or the lowermost 

 sometimes somewhat flexuous. 

 Panicle mostly more than 15 cm long, the branches several- 

 flowered; awns about 2 cm long. Sheaths with a villous 



line across the collar 25. A. wrightii. 



Panicle mostly less than 15 cm long, the branches few flowered; 

 awns 2 to several cm long. 



