34 



POACEAE. 



spikelets 2-6-flowered, compressed, the rachilla usually glabrous; 

 flowers perfect or rarely dioecious; glumes membranous, keeled, 

 1-3-nerved; lemmas membranous, keeled, awnless, longer than 

 the glumes, generally with a tuft of cobwebby hairs at the base, 

 5-7-nerved, marginal nerves usually pubescent, often also the 

 dorsal one; palea a little shorter than the lemma, 2-nerved or 

 2-keeled ; grain free, or sometimes adherent to the palea. 



Annual; lemma without cobwebby hairs at base. P. annua. 



Perennials. 



Plants with creeping rootstocks. 



Stems compressed, 2-edged; panicles small. P. compressa. 



Stems cylindric. 



Lemma webbed, that is with a tuft of hairs at base. P. pratensis. 

 Lemma without a tuft of hairs at base. P. olneyae. 



Plants tufted, without rootstocks. 

 Web present at base of lemma. 



Panicle close; leaf blades flat, thin and lax. P. bolanderi. 



Panicle open; leaf blades narrow, not thin and lax. 

 Ligule 3-5 mm. long; panicle loose, somewhat 



drooping, 10-30 cm. long. P. Iriflora. 



Ligule very short; panicle erect, 4-10 cm. long. P. nemoralis. 

 Web absent from base of lemma. 



Stems coarse and tall, 60^-100 cm. high. 



Leaves narrow, pale, involute; panicle narrow, 



erect. P. brachyglossa. 



Leaves flat, rarely involute, green or rarely 



glaucescent; panicle ample. P. ampla. 



Stems not coarse or tall, usually less than 60 cm. 



tall. 

 Leaves flat or folded, not filiform. 



Lemmas pubescent at base; leaves 1 mm. 



broad, usually folded. P. sandbergii. 



Lemmas puberulent at base; leaves 2 mm. 



broad, usually flat. P. saxalilis. 



Leaves involute and filiform. 



Florets close; ligule long. P. idahoensis. 



Florets loose; ligule short. P. capillarifolia. 



Poa annua L. Annual Bluegrass. Annual, the compressed stems 5-15 cm. 

 tall; leaves glabrous, the blades short and soft; panicle pyramidal, sometimes 

 1-sided; spikelets 3-7-flowered, crowded, 4 mm. long; lemma 3-3.5 mm. long, 

 not hairy at base. In moist places becoming common, apparently native 

 in the foothills. 



Poa compressa L. Canada Bluegrass. Usually low, spreading by root- 

 stocks and forming dense mats; the much compressed stems 15-40 cm. high, 

 decumbent at base, glabrous; panicle 3-7 cm. long, contracted, the branches 

 spikelet-bearing to the base or nearly so; spikelets 3-9-flowered; lemmas ob- 

 scurely nerved, the nerves slightly pubescent below. Sparingly introduced. 



Poa pratensis L. Kentucky Bluegrass. Perennial, with conspicuous run- 

 ning rootstocks, the terete stems 30-90 cm. tall; panicle pyramidal, open, 

 6-20 cm. long, the ascending or spreading branches in whorls of 3-5, spikelet- 

 bearing above the middle; spikelets 3-5-flowered ; lemmas 3-5 mm. long with 

 prominent intermediate nerves, silky-pubescent on the midnerve and margins, 

 cobwebby at the base. Everywhere introduced. 



