13 



BROMUS L. Gen. PL 15. 1737. 



Spikelet.s few to many-flowered, slightly or more rarely strongly flattened laterally, 

 in panicles, or rarely racemed; rachilla articulated above the emj^ty glumes and 

 between the florets; florets hermaphrodite or the uppermost imperfect; empty 

 glumes at the base of the spikelet 2, unequal, acute, or the second short-awned, 

 1 to 7 nerved, shorter than the flowering glumes; flowering glumes keeled or 

 more often rounded on the back, 5 to 9 nerved, usually 2-toothed at the apex, 

 awned from the back just below or from between the teeth, sometimes awnless; 

 awn straight or divergent, sometimes twisted. Palea usually a little shorter 

 than the glume, 2-keeled. Stamens usually 3. Stigmas plumose, sessile, spring- 

 ing from below the hairy cushion-like apex of the ovary. Grain furrowed and 

 grown to the palea. Annual or perennial grasses with flat leaves and rather 

 large, erect or pendulous spikelets. 



The genus is very closely related to Festuca, from which it differs in general in its 

 larger spikelets, more or less dentate apex to the flowering glume and in the 

 character of the ovary, and the habit of growth which is very rarely csespitose. 

 Some species show close relationship with Avena, Trisetum, and Danthonia, while 

 others are very close to Melica. 



ANALYTICAL KEY TO THE SPECIES AND VARIETIES. 



1. Flowering glmne with pubescence about equally distributed over the whole dor- 

 sal surface 2 



1. Flowering glume with pubescence conspicuously unevenly distributed over the 

 dorsal surface, longest and densest on the margins or base or both 25 



1. Flowering glume smooth or scabrous So? 



2, Spikelets 5-9 mm. broad, laterally flattened before flowering 3 



2. Spikelets usually less than 5 mm. broad ] )ef ore flowering and terete or subterete . 6 



3. Awn not exceeding 7 mm. long, usually shorter 4 



3. Awn usually more than 7 mm. long 24 



4. Leaves linear, somewhat involute and pilose-pubescent .. 30 B. subvelutinus. 



4. Leaves linear-lanceolate, flat 5 



5. Panicle narrow, lower branches not exceeding 10 cm. long. 31 B. marginatus. 



5. Panicle rather broad, some of the lower branches exceeding 10 cm. long 



31 B. marginatus latior. 



6. Panicle rather lax and drooping in flower 7 



6. Panicle as a whole not conspicuously secund or drooping in flower 17 



7. Perennials, native 8 



7. Annual, introduced 14 B. tectorum. 



8. Species restricted to the Rocky ^lountains and westward 9 



8. Species east of the Rocky Mountains 14 



9. Lower empty glume l-nerved, lanceolate, acute 10 



9. Lower empty glume 3-nerved, broadly lanceolate, subacute 19 B. porteri. 



10. Lower empty glume 5 mm. or more long 11 



10. Lower empty glume usually less than 5 mm. long. . . 19y5 B. porteri havardii. 



11 . Sheaths densely pilose-pubescent 19a: B. porteri lanatipes. 



11 . Sheaths not densely pilose-pubescent 12 



12. Empty glumes more or less pubescent 13 



12. Empty glumes smooth 1 9^ B. porteri frondosus. 



13. Culm tall, stout; panicle heavy 20 B. pacificus. 



13. Culm rather slender; panicle not heavy 23 B. vulgaris. 



14. Lower empty glume l-nerved, acute 15 



14. Lower empty glume more or less distinctly 3-nerved 18 B. kalmii. 



