LAMSON-SORIBNKR AND MERRILL — GRASSES OF ALASKA. 67 



the dorsal and marginal nerves usually soft-hairy and often with a tuft of long, cob- 

 webby hairs at. the base, rarely glabrous. Annual or perennial grasses with usually 

 open panicles. 



Annuals 1. P. annua. 



Perennials. 



Culms slender, rarely exceeding 30 cm. in height. 

 Leaves short, 2 to 4 mm. wide, abruptly acute. 



Leaves firm, rigid; panicle branches short, spread- 

 ing, densely flowered 2. P. alpina. 



Leaves thin, soft; panicle branches elongated, slen- 

 der, ascending, few-flowered 4. P. glacialis. 



Leaves usually elongated, 2 mm. wide or less, gradually 

 narrowed to the apex. 



Lemmas pubescent on the back below 3. P. arnica. 



Lemmas glabrous between the nerves. 



Basal leaves thin, soft, elongated, the panicle 



branches spreading 5. P. paueispieula . 



Basal leaves rallur firm, .^hort, often somewhat 

 involute, the panicle branches ascending. . . 6. P. lam. 

 Culms usually much exceeding 30 cm. in height, mostly stout. 

 Spikelets exceeding 6 mm. in length. 



Leaf blades narrow, 3 mm. wide or less. 



Panicles elongated, narrow, often nodding, the 



branches ascending 13. P. stenantha. 



Panicles ovate, open, erect, the branches spread- 

 ing 14. P. acutiglumis. 



Leaf blades 4 to 10 mm. wide. 



Panicles ovate, densely flowered, 2 to 4 cm. in 

 diameter, the branches short, ascending, 



flower-bearing throughout 17. P. trinii. 



Panicles open, the branches naked below, 

 spreading or ascending. 



Panicle branches straight, rigid 18. P. eminens. 



Panicle branches flexuous. 



Panicles erect 16. P. lanata. 



Panicles nodding, leaf blades rather 



soft; lemmas 7 mm. long 15. P. turneri. 



Spikelets 6 mm. or less in length. 



Lemmas 4 to 6 mm. long; panicles contracted; lem- 

 mas not webbed at the base 13. P. stenantha. 



Lemmas less than 4 mm. long. 



Pedicels commonly shorter than the spikelets. 



Lemmas obscurely nerved 7. /'. tri flora. 



Lemmas prominently nerved. 



Lateral nerves silky-villous 10. P. pratensis. 



Lateral nerves glabrous 9. /'. trivialis. 



Pedicels equaling or much exceeding the spike- 

 lets. 

 Spikelets 5 to 6 mm. long; panicle branches 



glabrous 12. P. leptocoma. 



Spikelets less than 5 mm. in length; panicle 

 branches scabrous. 



Leaf blades thin, soft, flaccid; lemmas 



3 mm. long 11. P. rotundata. 



Leaf blades firm; lemmas 2.5 mm. long. 8. P. neinoralis 



