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. 

 Perennials. 



Plants with creeping rootstocks. 



Stems compressed, 2-edged; panicles small. 

 Stems cylindric. 



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

 Lemma without a tuft of hairs at base. 

 Plants tufted, without rootstocks. 

 Web present at base of lemma. 



Panicle close; leaf blades flat, thin and lax. 

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

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



drooping, 10-30 cm. long. 

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

 Web absent from base of lemma. 



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



Leaves narrow, pale, involute; panicle narrow, 



erect. 

 Leaves flat, rarely involute, green or rarely 



glaucescent; panicle ample. 

 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. 

 Lemmas puberulent at base; leaves 2 mm. 



broad, usually flat. 

 Leaves involute and filiform. 

 Florets close; ligule long. 

 Florets loose; ligule short. 



P. annua. 



P. compressa. 



P. pralensis. 

 P. olneyae. 



P. bolanderi. 



P. Iriflora. 

 P. nemoralis. 



P. brachyglossa. 

 P. ampla. 



P. sandbergii. 

 P. saxalilis. 



P. id.ahoeni.is. 

 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. 



