GRASS FAMILY 



33 



III. Platyphyllae. 



Ligules tnincate or abruptly acute 

 Ligules lanceolate, long attenuate. 



5. P. ocddenlalis. 



6. P. callida. 



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; 



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. high, not cespitose, with a creeping rootstock; 

 floral glumes acuminate. 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. 

 Intermediate nerves of the lemma glabrous; plant usually over 3 dm. high; 



stem-leaves several, flat and flaccid. 

 Hairs of the miduerves and lateral nerves copious and spreading. 

 Lemma ovate, abruptly acute, usually purple. 13. P. reflexa. 

 Lemma lanceolate, gradually acute, usually pale green. 



14. P. nervosa. 

 Hairs of the midnerves and lateral nerves few and appressed or none. 



15. P. leptocoma. 

 Cobweb lacking; internerves and the intermediate nerves glabrous; midnerves and 



lateral nerves hairy; habit like P. arctica. 16. P. alpicola. 



V. COMPRESSAE. 



One species. 



VI. APERTAE. 



Branches of the inflorescence short, usually in pairs. 

 Branches of the inflorescence very long, in 3's to 5's. 



17. P. compressa. 



18. P. aperta. 



19. P. macroclada. 



VII. Tkiflorae. 

 Lemma 5 mm. long. " 4. P. rhizomata. 



Lemma 3 mm. long or less. 



Stem stout; leaves 2-5 mm. wide; ligule 3-4 mm. long, triangular; branches of the 

 panicle at last spreading; second glume narrower than the lemma, three- 

 fourths as long or more. 20. P. triflora. 

 Stem slender; leaves seldom over 2 mm. wide; ligule about 1 mm. long, truncate; 

 branches of the panicle ascending or erect. 

 Flowers green; the second empty glume with broad, scarious margins and strong 

 lateral nerves 

 Inflorescence with erect branches; second empty glume narrower than the 



lemma. 21. P. subtrivialis. 



Inflorescence with ascending branches; second empty glume not narrower 

 than the lemma. 22. P. interior. 



Flowers usually purple-tinged; scarious margin of the empty glumes scarcely 

 evident and lateral nerves faint. 23. P. crocata. 



One species. 



VIII. Alpinae. 



IX. Whbelerianae. 



24. P. alpina. 



Lower sheaths retrorsely strlgulose. 



Internerves of the acute lemma merely strigulose or scabrous. 

 Nerves of the lemma scabrous; Ugules short, truncate. 



Branches of the inflorescence ascending. 25. P. Olneyae. 



Branches of the Inflorescence reflexed. 26. P. subreflexa. 



Nerves of the lemma silky or villous on the lower portion. 



Ligules 2 mm. long, truncate; leaf-blades narrow, ascending. 



27. P. Wheeleri. 

 Ligules 4-5 mm. long, lanceolate, acuminate; leaf-blades broad, spreading 



30. 

 31. 



Vaseyana. 

 tricholepis. 



Tracyi. 

 curta. 



Internerves of the obtusish lemm.a villous, at least below. 

 Leaf-sheaths all glabrous and smooth. 

 Ligules lanceolate, acute, 3 mm. long. 

 Ligules truncate, about 1 mm. long. 



X. Phoeniceae. 



Plant tall, 4 dm. high or more; nerves and internerves of the lemma villous. 



32. P. Gray ana. 



Plant low, usually less than 3 dm. high; internerves of lemma glabrous. 



■^ 16. P. alpicola. 



