84 MISC. PUBLICATION 42 3, U. S. DEPT. OF AGRICULTURE 



Key to the species 



1. Spikelets flattened, the glumes and lemmas compressed-keeled: Section Cera- 

 tochloa (2). 

 2. Lemmas awnless or nearly so, light green, the margins usually pale. 



1. B. CATHARTICUS. 



2. Lemmas distinctly awned, dark green throughout (3). 



3. Awns more than 7 mm. long 2. B. carinatus. 



3. Awns less than 7, usually 5 to 6 mm. long (4) . 



4. Sheaths and lemmas pubescent 3. B. marginatus. 



4. Sheaths glabrous; lemmas glabrous or scabrous 4. B. polyanthus. 



1. Spikelets not conspicuously flattened, the lemmas rounded on the back (5). 

 5. Plants perennial: Section Bromopsis (6). 



6. Rhizomes present; lemmas nearly awnless 5. B. inermis. 



6. Rhizomes wanting (7). 



7. Lemmas villous-ciliate on the margins, pubescent on the lower part of 



the back, the upper portion glabrous 6. B. ciliattjs. 



7. Lemmas evenly pubescent or pilose on the back, the pubescence some- 

 times sparse (8). 

 8. Culms usually less than 60 cm. high; panicles less than 10 cm. long, 

 with lax, few-flowered branches; first glume 3-nerved. 



7. B. ANOMALUS. 

 8. Culms usually 80 to 120 cm. high; panicles more than 10 cm. long, 

 with relatively stiff branches; first glume 1-nerved (9). 

 9. Panicle branches short, stiffly ascending or spreading, few-flowered; 



spikelets appressed, short-pediceled 8. B. orcuttianus. 



9. Panicle branches long, arcuate-spreading; spikelets long pediceled 

 (10). 

 10. Lower sheaths glabrous or nearly so; leaf blades mostly less 



than 5 mm. wide 11. B. frondosus. 



10. Lower sheaths usually conspicuously retrorse-pilose ; leaf 

 blades more than 5 mm. wide (11). 

 11. Culms leafy, many-noded; sheaths much longer than the 



internodes; blades often auriculate 9. B. latiglumis. 



11. Culms few-noded; sheaths usually shorter than the inter- 

 nodes; blades not auriculate 10. B. PURGANS. 



5. Plants annual (12). 



12. Awns geniculate; teeth of the lemma aristate 20. B. trinii. 



12. Awns straight or somewhat spreading; teeth of the lemma not aristate 

 (13). 

 13. Lemmas narrow, acuminate, hyaline toward the tip: Section Eubromus 

 (14). 

 14. Panicle dense, contracted; culms pubescent below the panicle. 



17. B. RUBENS. 

 14. Panicle open, the branches widely spreading (15). 



15. Panicle branches slender; pedicels flexuous; awns 12 to 14 mm. 



long 18. B. TECTORUM. 



15. Panicle branches relatively stout; pedicels straight; awns 3.5 to 



5 cm. long 19. B. rigidus. 



13. Lemmas broad, acute (16). 



16. Panicle dense, the branches appressed (17). 



17. Spikelets glabrous 12. B. racemosus. 



17. Spikelets pubescent 13. B. mollis. 



16. Panicle open, the branches spreading (18). 



18. Panicle branches stout, stiffly spreading or drooping; lemmas firm. 



14. B. COMMUTATUS. 



18. Panicle branches slender, flexuous; lemmas rather thin (19). 



19. Palea much shorter than the lemma 15. B. japonicus. 



19. Palea as long as the lemma 16. B. arvensis. 



1. Bromus catharticus Vahl, Symb. Bot. 2: 22. 1791. 



Bromus unioloides H. B. K., Nov. Gen. et Sp. 1: 151. 1815. 



Mohave, Maricopa, and Pima Counties, a weed in waste places, 

 especially around Tucson, May to September. Southern United 



