198 



POACEAE 



Keel and lateral nerves villous. 



Sheaths retrorsely scaberulous; culms 1-1.5 meters tall. 17. P. occidentalis. 



Sheaths glabrous or very slightly scaberulous. 



Plants of the Alpine Zone, low and tufted; web scant. 16. P. Icptocoma. 



Plants of the Transition Zone, mostly 50-100 cm. tall; web abundant. 



18. P. pahistns. 



l.emma with no tuft of cobwebby hairs at base. 



Blades short and flat, 2-5 mm. wide; an alpine plant. 19. P. alpiiia. 



Blades long and slender, mostly folded or involute. 

 Blades soft and lax, flat or loosely involute. 



Panicles long-exserted; culms stiffly erect; plants of alpine regions. 20. P. vnpicola. 

 Panicles short-exserted; culms somewhat decumbent at base; plants of the seacoast. 



21. P. pachypholis. 

 Blades firm and stiff, mostly basal, the panicles long-exserted; plants of deserts. 



Ligule 5-7 mm. long, acute. 22. P. longUigula. 



Ligule short, rounded or truncate. 23. P. fendlenana. 



Lemma not villous on nerves nor with tuft of cobwebby hairs at base, sometimes pubescent on lower 

 part of back. 

 Lemma minutely pubescent on the lower half or third, the hairs somewhat curled. 



Sheaths scaberulous; panicle usually narrow and rather long, the branches short and appressed. 



24. P. scabrclla. 



Sheaths smooth. 



Culms decumbent and loose at base; plants usually lax; panicle open, the branches slender, 



spreading. ^5. P. graciUiina. 



Culms erect trom a densely tufted base; panicle narrow, the branches appressed except 

 during anthesis. 

 Plants slender, averaging less than 30 cm. tall; blades in a short basal cluster, usually 



folded. -^- P- saiidbergii. 



Plants stout, averaging over 50 cm. tall; blades not usually conspicuously basal, usually 

 flat. 27. P. can by I. 



Lemmas glabrous or scabrous. 



Panicle narrow, mostly over 10 cm. long, the branches appressed, except in anthesis; plants ro- 

 bust, usually over 50 cm. tall. 

 Sheaths scabrous; ligule long. 28. P. iiciadensis. 



Sheaths smooth; ligule short. 



Blades flat. 29. P. awp'a. 



Blades involute. 30. P. brachyglossa. 



Panicle short, compact or open, less than 10 cm. long. 



Blades of the culm flat, those of the lower culm 2-i mm. wide; alpine grasses. 



Panicle rather loose, short-exserted, mostly green; culms low, in tufts from firm branched 



caudices. 31. P. curUfoha. 



Panicle compact, spikelike, Icng-exserted, mostly purple; culms 20-40 cm. tall, slender, 

 mostly solitary or few in a tuft. 32. P. epilis. 



Blades narrow or filiform, usually folded or involute. 



Panicle oblong, compact and spikelike, 2-6 cm. long, 1-2 cm. thick: I'^nts of seacoast 



(-lifls 33. P. unilateralis. 



Panicle open, or if narrow, few-flowered; plants of the interior. 



Panicle short and open, few-flowered, the capillary branches bearing 1-2 spikelets; 



culms 10-20 cm. tall. 34. P. vaseyochloa. 



Panicle narrow and few-flowered or somewhat open and many-flowered. 



Panicle somewhat open; blades filiform, scabrous; plants of the Arid Transition 



2one. 35. P. cusickii. 



Panicle narrow, the branches short and appressed; blades short and narrow.^rather 

 firm, glabrous; plants of the alpine regions. 

 Glumes 4-5 mm. long; panicle shining, usually pale. 36. P. pniiglet. 



Glumes 3 mm. long; panicle usually purple. 



Blades more than 5 cm. long; panicle long-exserted. 37. P. Icibcrgh. _ 

 Blades less than 5 cm. long; panicle short-exserted. 38. P. Icttcnnam. 



1. Poa annua L. 



Annual Bluegrass. Fig. 453. 



Poa annua L. Sp. PL 68. 1753. 



Poa infirma H. B. K. Nov. Gen. & Sp. 1: 158. 1816. 



Poa aestivalis Presl, Rel. Haenk. 1: 272. 1830. 



Annual, tufted, bright green, glossy ; culms flatten- 

 ed, decumbent at base, sometimes rooting at the 

 lower nodes; sheaths loose; blades soft and lax; 

 panicle pyramidal, open, 2)-7 cm. long: spikelets 

 crowded, 3-6 flowered, about 4 mm. long; lemma not 

 webbed at base, distinctly 5-nerved, the nerves pilose 

 on lower half. 



Open ground, along roadsides and in waste places, Alaska 

 to Mexico, east to the Atlantic Ocean; introduced from 

 Europe. Jan.-Tune. Type locality, European. 



