GRASS FAMILY 73 



Branches of the inflorescence in fruit reflexed or at least spreading; lemma 

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

 Spikelets many, light 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 usual! j- in 2's, rarely in 3's, spikelet- 

 bearing towards the ends. IV. Reflexae. 



Intermediate nerves of the lemma faint or obsolete. 



Stem compressed; lemma obtuse. V. Compressae. 



Stem not compressed; lemma acute or acuminate. 



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

 Branches of the panicles not reflexed. VII. Trifixjrae. 



Cobweb wanting. 



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

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



VIII. Alpixae. 

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

 keels. 

 Plants with horizontal creeping rootstocks; not bimch-grasses. 



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



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



Spikelets not strongly compressed; lemma neither strongly compressed 



nor strongly nerved (except in P. pra^ensj/ormis), not conspicuously 



scabrous. 



Lemma acuminate, dark purple; innovations extravaginal. 



X. Phoexice.\e. 

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

 tions both extra- and intra vaginal. XI. Arid.\e. 

 Plants without extravaginal rootstocks; densely tufted bunch-grasses. 

 Lemma 3-4 mm. long. 



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



lemma ovate. XII. Rupicol.\e. 



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

 lanceolate in side-view. XIII. Multxoiiae. 



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 interuerves; 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. Fexdleriax.\e. 

 Spikelets little flattened; lemma roimded on the backs towards the 

 apex, almost straight, obtuse. XVII. Bt:cKLETAXAE. 



I. AXNUAE. 



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



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



II. Pr.\texses. 



Lemma .3-4 mm. long; ligule trimcate. 3. P. pratensis. 



Lemma 5 mm. long; ligule not truncate. 4. P. rhizomala. 



III. Plattphtllae. 



Ligules truncate or abruptly acute. 5. P. occidenlalis. 



Ligules lanceolate, long attenuate. 6. "P. caUida. 



IV. Reflexae. 

 Cobweb present but often scant. 



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



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; 



thoseof 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. high, not cespitose, with a creeping rootstock; 

 floral glumes acimiinate. 10. P. longipila. 



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



11. P. callichroa. 

 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. 



