15. Ligules thin and membranous, rarely ciliolate, usually acute, those of the 

 innovations and lower culm leaves usually over 1 mm. long, those 

 of the upper culm leaves mostly 2-7 mm. long 9. P. nevadensis. 



1. Poa compressa L. Canada bluegrass. 



Perennial; culms basally long-decumbent, stoloniform or subrhizomatous, 

 strongly compressed, 1-2.5 mm. broad, with 2 longitudinal keels; aerial culms 

 ascending, somewhat geniculate; lower sheaths shorter than the internodes; blades 

 3-12 cm. long, 1-3 mm. broad, flat or folded; panicles conic-cylindric, 3-10 cm. 

 long, open with few short branches per whorl rather strikingly ascending; pedicels 

 5-10 mm. long; spikelets crowded, laterally compressed, 3- to 6-flowered; lowest 

 lemma 2-3 mm. long, firm, green-stramineous, keeled, 5-nerved, the lower part 

 of the midnerve and marginal nerves minutely pubescent, the very obscure inter- 

 mediate nerves and internerve areas glabrous, basally with very short scant tuft 

 of silky hair or this absent. 



Tame pastures, wet meadows and in marshy soil, in Okla. (Waterfall) and 

 n.-cen. Tex. and the Rio Grande Plains, probably elsewhere, not persistent but 

 repeatedly introd., N.M. (Taos, San Miguel and Colfax cos.) and Ariz. (Apache, 

 Navajo, Coconino, Graham and Gila cos.), spring; nat. of Eur., now widely 

 introd. in Am. 



2. Poa pratensis L. Kentucky bluegrass. Fig. 84. 



Tufted perennial with fragile rhizomes 1-2 mm. thick and to 2 dm. long; 

 aerial culms 3-6 dm. long, mostly erect, slightly flattened but not two-keeled; 

 ligule a short usually erose scale; blades thin, 2-4 mm. broad, flat or folded, 

 basally not markedly broader than the top of the sheath; panicles 5-13 cm. long, 

 conical, usually open and with a whorl of 5 flexuous basally naked branches at 

 the lowest node, the successively higher nodes with fewer branches; pedicels 

 0.5-1.5 mm. long; spikelets somewhat laterally compressed, crowded, 4- to 

 6-flowered; lowest lemma 3-4 mm. long, green with a broad thin whitish margin, 

 dorsally keeled, 5-nerved, the lower part of the midnerve and marginal nerves 

 pubescent, the intermediate nerves and internerve area glabrous, basally with a 

 long tuft of flexuous silky hairs. 



Meadows and tame pastures, and in wet soil on edge of lakes and ponds, in 

 n.-cen., e. and Trans-Pecos Tex., infrequent and probably not persistent, N. M. 

 (Sandoval Co.) and Ariz. (Apache to Mohave, s. to Cochise, Santa Cruz and Pima 

 COS.), spring; nat. of Euras., now widely introd. in moist temp, areas of N.A. and 

 S.A. 



3. Poa glaucifolia Scribn. & Williams. 



Plants glaucous; culms in loose tufts, 6-10 dm. tall; blades 2-3 mm. wide; 

 panicle narrow, open, mostly 1-2 dm. long, the branches usually in somewhat 

 distant whorls, mostly in threes, ascending, very scabrous, naked below; spikelets 

 2- to 4-flowered; glumes 4-5 mm. long; lemmas about 4 mm. long, villous on 

 the lower half of the keel and marginal nerves and more or less so on the inter- 

 mediate nerves below. 



In wet meadows, ditches and stream bottoms, in N.M. (Hitchcock) and Ariz. 

 (Coconino Co.), July-Aug.; B.C. and Alta. to Minn., Neb., N.M., Ariz, and Nev. 



4. Poa Grayana Vasey Arctic bluegrass. 



Culms loosely tufted, erect from a decumbent base, 1-3 dm. tall; ligule pointed, 

 to 4 mm. long; blades mostly basal, flat or folded, mostly 2-3 mm. wide, with 

 one short blade about the middle of the culm; panicle open, pyramidal, 5-10 cm. 

 long, the lower branches usually 2 and spreading or sometimes reflexed, bearing 

 a few spikelets toward the tip; spikelets 5-8 mm. long, 3- or 4-flowered; lemmas 

 densely villous on the keel and marginal nerves and pubescent on the lower part 



189 



