POACEAE. 53 



Dioecious, seashore plant ; spikelets 10-15 mm. 



long. p. macrantha. 



Perfect; spikelets 4-5 mm. long. P. pratensis. 



Lemma not webbed. 



Low seashore plant with narrow involute leaves 



and small panicle; spikelets close. P. confinis. 



Taller grass, not maritime, with flat or folded 



leaves; spikelets loose. P. nervosa. 



Plants tufted, without rootstocks. 



Lateral nerves ot lemmas prominent; web present. P. trivialis. 



Lateral nerves of lemmas not prominent. 

 Web present at base of lemma. 



Leaves flat or folded, not soft and flaccid. 



Panicle short pyramidal; spikelets 6-7 mm. 



long; low alpine plant. P. arctica. 



Panicle ample, spreading; spikelets 3-4 mm. 



long. P. triflora. 



Leaves flat, rather short, soft and flaccid. 



Panicle lax and spreading; spikelets 5-6 mm. 



long; florets not early deciduous. P. leptocoma. 



Panicle narrow, the rays usually erect; 



florets early deciduous. 



Lemma glabrous or nearly so. P. bolanderi. 



Lemma pubescent. P. howellii. 



Web absent, no tuft of hairs at base of lemma. 

 Nerves of the lemma pilose below. 



Alpine plant ; leaf blades flat, green, broad. P. alpina. 

 Maritime plant; leaf blades narrow or 



folded, glaucescent. _ P. pachypholis. 



Nerves of the lemma not pilose. 



Stems low, 5-20 cm. high; grasses of the 



highest mountains. 

 Leaves soft; panicle purple, very short; 



plants 5-10 cm. high. P. lettermani. 



Leaves rather rigid; panicle pale, narrow, 



elongated; plant 10-20 cm. high. P. suksdorfii. 



Stems taller, usually 20-40 cm. high, mostly 



grasses of rupestrine habitat. 

 Panicle close, erect; leaves flat. 



Lemmas pubescent at base; leaves 



rather narrow, sometimes folded. P. sandbergii. 

 Lemmas glabrous; leaf blades 



broader. P. paddensis. 



Panicles loose; leaves narrow, flat or 



involute. 



Ligules of the sterile shoots obsolete; 

 of the stem leaves short and trun- 

 cate. P. multnomae. 

 Ligules well developed on all the 



leaves. 

 Rays of the panicle in about 5 



series; ligules 2-5 mm. long P. alcea. 

 Rays of the panicle in fewer 

 series; ligules 1-2 mm. long. 

 Panicle close; glumes firm; 



blades flat. P. saxatilis. 



Panicle loose; glumes thin; 



blades involute. P. gracillima. 



