GRASS P^AMILY 73 



Branches of the iullorescence hi fruit reflexed or at least spreading; lemma 

 usually acuminate or very acute; cobweb scant or sometimes none. 

 Spikelets many, li^ht green; branches of the inflorescence numerous, the 



lower in 3's, or 4's, or o's; rootstock creeping. III. Pl.\typhyll.\e. 



Spikelets few, usually more or less purple, except in P. leptocoma; branches 

 of the inflorescence few, the lower usually in 2's, rarely in 3's, spikelet- 

 bearing towards the ends. IV. Reflex.^e. 



Intermediate nerves of the lemma faint or obsolete. 



Stem compressed; lemma obtuse. V. Compre.ssae. 



Stem not compressed ; lemma acute or acuminate. 



Branches of the panicles reflexed; rootstock creeping. VI. Apertae. 

 Branches of the panicles not reflexed. VII. Triflorae. 



Cobweb wanting. 



Spikelets rounded at the base; empty glumes very broad and their keel strongly 

 arched ; low tufted perennials, with short open panicle and broad leaves. 



VIII. ALPINAE. 



Spikelets acute at the base; empty glumes narrower, not strongly arched on their 

 keels. 

 Plants with horizontal creeping rootstocks; not buncli-grasses. 



Spikelets strongly compressed; lemma strongly keeled, strongly 5-nerved, 



conspicuously scabrous; glumes very acute. IX. \Vheeleri.\xae. 



Spikelets not strongly compressed; lemma neither strongly compressed 



nor strongly nerved (except in P. pra(fnsf/or-7?HS), not conspicuously 



scabrous. 



Lemma acuminate, dark purple; innovations e.xtravaginal. 



X. Phoexice.\e. 

 Lemma obtuse or acutish, green or merely tinged with purple; innova- 

 tions both extra- and intra vaginal. XI. Aridae. 

 Plants without extra vaguial rootstocks; densely tufted bunch-grasses. 

 Lemma 3-4 mm. long. 



Low alpine plants, with narrow panicles of few purplish spikelets; 



lemma ovate. XII. Rupicol.ae. 



Slender plants, 4-.5 dm. high, with open panicles; lemma narrowly 

 lanceolate in side-view. XIII. Multxomae. 



Lemma .5 mm. long or more; plants comparatively robust. 



Spikelets decidedly flattened; lemma acute and keeled on the back. 

 Pubescence on the nerves of the lemma, if any, not stronger than 

 on the internerves; flowers perfect. 

 Inflorescence dense and spike-like. XIV. Epile.s. 



Inflorescence open; branches spikelet-bearing towards their 

 ends. XV. Gracillimae. 



Pubescence of the nerves of the lemma villous or pilose, that of the 

 internerves none or almost none; plants dioecious. 



XVI. Fexdlerianae. 

 Spikelets little flattened; lemma ro4.mded on the backs towards the 

 apex, almost straight, obtuse. XVII. Buckleyan.\e. 



I. AXXUAE. 



Low, 1-2 dm. high; branches of the panicle spreading. 

 Taller, erect, 2-5 dm. high ; branches of the panicle erect. 



II. Pr.\tenses. 

 Lemma 3-4 mm. long; ligule trmicate. 

 Lemma 5 mm. long; ligule not trtmcate. 



III. Pl.\typhyll.\e. 

 Ligules truncate or abruptly acute. 

 Ligules lanceolate, long attenuate. 



IV. Reflexae. 

 Cobweb present but often scant. 



Lemmas obtuse; cobweb dense. 7. P. lanala. 



Lemmas acute or acuminate; cobweb scant. 



Internerves of the lemma more or less pubescent, at least below. 



Spikelets 3-4-flowered; stem-leaves usually folded or involute; plant usually 

 less than 3 dm. high, tufted. 

 Internerves of the lemma short-pubescent below; leaves filiform, involute; 



those of the sterile shoots usually arcuate. 8. P. cenisia. 

 Internerves of the lemma long-hairy, at least below; leaves 1-2 mm. wide, 

 usually conduplicate, rather firm. 

 Plant low, 1-3 dm. high, usually cespitose; lemma acute. 



9. P. arctica. 

 Plant tall, 3-5 dm. liigh, not cespitose, with a creeping rootstock; 

 floral glumes acuminate. 10. P. lonqipila. 



Spikelets 5^7-flowered; leaves all flat, 3-4 mm. wide; stem fully 3 dm. high. 



11. P. callichma. 

 Internerves of the lemma glabrous; plants with creeping rootstocks. 



Intermediate nerves of the lemma pubescent; plant 3 dm. or less high; leaves 

 mostly basal, firm; stem-leaves 1-2, usually conduplicate. 



12. P. pudica. 



