POACEAE. 27 



Spikelets not articulated below the 

 empty glumes. 

 Empty glumes saccate at the base, 

 several times larger than the 

 flowering glumes; inflorescence 

 spike-like. 18. Gastridium. 



Empty glumes not saccate, never 

 exceeding the flowering glumes 

 more than a third. 

 Empty glumes smooth or minute- 

 ly scabrous along the keel. 17. Agrostis. 

 Empty glumes more or less 



hairy; inflorescence spike-like. 13. Alopecurus. 

 Flowering glumes awnless. 



Pericarp free from the grain. ^ 14. Sporobolus. 



Pericarp closely adherent to the grain. 



Empty glumes abruptly awn-pointed. 12. Phleum. 

 Empty glumes not abruptly awn- 

 pointed. 17. Agrostis. 



9. ARISTIDA L. Triple-awned Grass. 



Plants various in habit and inflorescence, with very 

 narrow, often involute setaceous leaves. Spikelets nar- 

 row, 1-flowered. Glumes 3, narrow, the 2 empty ones 

 carinate; the third rigid and convolute, bearing 3 awns, 

 sometimes rudimentary or rarely wanting. Palea 2- 

 nerved. Stamens 3. Styles distinct. Grain free, tight- 

 ly enclosed in the glumes. 



1. A. bromoides H. B. K. Culms slender, branching below and 

 tufted, 8-35 cm. high; sheaths shorter than the internodes; ligule 

 reduced to a short fringe; sterile shoots few, the leaves 2-8 cm. long, 

 involute, setaceous, scabrid above; panicle exserted, spike-like, 

 secund, purplish, 2-5 cm. long; spikelets on short pedicels; empty 

 glumes narrow, linear, abruptly pointed, scabrous on the back, the 

 first 3-5 mm. long, second 5-9 mm. long; flowering glume scabrous 

 on the keel, about as long as the second glume; central awn shorter 

 to a little longer than its glume, the lateral ones a little shorter, all 

 scabrous; palea less than 1 mm. long. 



Occasional in dry open places in the chaparral belt about Pasa- 

 dena and San Diego; Catalina Island. 



2. A. purpurea Nutt. Rather stout, tufted, glabrous, 3-6 dm. 

 high; culms simple; sheaths longer than the internodes, pilose at the 

 throat; leaves involute, the lower numerous, 3-10 cm. long, 1-2 mm. 

 wide, those of the culm about 3, usually 3-4 cm. long; panicle 

 purplish, the branches capillary, generally erect or ascending, usu- 

 ally many-flowered, 3-5 at each node; spikelets pale or purplish; 

 second empty glume twice as long as the first, equaling the flowermg 

 glume, both cleft at the apex, the midnerve excurrent as a scabrous 

 awn, 1-2 mm. long; flowering glume about 10 mm. long, strongly 



