THISTLE FAMILY 235 



Leaves and branches white-tomentose. 



Leaves mostly erect, the upper reduced, not exceeding the heads. 



6. C. Newberryi, 

 Leaves arcuate-spreading, the upper longer than the heads. 



7. C. Howardii. 

 Outer bracts short, neither produced nor foliaceous. 



Heads 5-8 mm. high; bracts thin, grabrous. 



Leaves 2-3 cm. long, over 1 mm. wide, light green. 8. C. Greenei. 

 Leaves 1-2 cm. long, less than 1 mm. wide, dark green. 



9. C. filifolius. 

 Heads about 1 cm. long; bracts thicker. 



Leaves less than 1 mm. wide; bracts glabrous. 10. C. albidus. 

 Leaves 1 mm. broad or broader; bracts arachnoid-ciliate. 



Leaves 1-2 cm. long; involucre lanate as well as arachnoid. 



11. C. collinus. 

 Leave? 3-6 cm. long; involucre somewhat viscid, merely arachnoid- 

 ciliate on the margin. 12. C. wyomingensis. 

 Bracts not acuminate. . * 



Bracts 6-7 in each vertical row. 13. C. formosus. 



Bracts 3-5 in each vertical row. 



Achenes pubescent; bracts acute or obtuse. 



Branches, at least when young more or less whitened with a pannose tomeu- 

 . tum; style-appendages longer than the stigmatic portion; corolla 7-12 

 mm. long. 

 Bracts and mature leaves perfectly glabrous. 



Bracts orate, or the outer triangular; involucre about half as long as 



the flowers. 14. C. virens. 



Bracts lanceolate to linear; involucre more than half as long as the 

 flowers. 

 Leaves nearly erect or strongly ascending, straight, 1-2 mm. wide. 



15. C. graveolens. 

 Leaves scarcely 1 mm. wide. 



Leaves spreading or reflexed, more or less falcate; lobes of the 



coroUas lanceolate, mostly acute. 10. C. patens. 



Leaves erect, about 0.5 mm. wide; lobes of the corolla ovate, 

 obtuse, about 0.5 mm. long, erect in age. 



17. C. pinifolius. 

 Bracts erose-ciliate on the margin, or tomentose, or both. 



Inflorescence elongate-thyrsoid. 18. C. concolor. 



Inflorescence corymbiform, flat or round-topped. 



Bracts lanceolate, acute; leaves less than 2.5 mm. wide. 

 Bracts more or less erose-ciliate on the thin margins. 



Mature leaves glabrous or nearly so, about 1 mm. wide, erect. 



19. C. oreophilus. 

 Mature leaves more or less densely white-tomentose; bracts 



lanceolate. 

 Leaves 1 mm. wide or less, spreading. 



20. C. plattensis. 

 Leaves 1-2.5 mm. wide. 



Bracts narrow, Unear-lanceolate, strongly carinate, 

 almost glabrous, except the erose-ciliate margins. 



21. C. pulcherrimus. 

 Bracts usually broader, more or less densely tomentose 



and viscid as well as ciliate. 

 Stems equally leafy throughout; leaves aU alike, 

 strongly ascenduig; bracts strongly carinate. 



22. C. JTigidus. 

 Stems more leafy towards the ends; upper leaves 



much shorter; bracts slightly carinate. 



23. C. palUdus. 

 Bracts not at all ciliate on the thicker margin, but white-tomen- 

 tose on the back. 



Bracts soai-cely carinate; older branches not densely and 



thickly woolly. 24. C. spedosus. 



Bracts strongly carinate; older branches densely and thickly 

 woolly. 25. C. nauseosus. 



Bracts elliptical, nearly glabrous, the thinner ones obtuse; leaves 

 3—4 mm. wide. 26. C. salicifolius. 



Branches without tomentum; style-appendages shorter than the stigmatic por- 

 tion; corolla 5-7 mm. long. 

 Leaves and the white or straw-colored stem glabrous or nearly so, except 

 the hispidiUous-ciliate margins of the former. 

 Leaves narrowly linear, 2 mm. wide or less. 



Bracts neither strongly carinate nor with conspicuous green tips. 

 Leaves less than 1 mm. wide, l-nerved. 



Bracts linear, the innermost rounded at the apex. 



27. C. stenophyllus. 

 Bracts ovate-lanceolate, acute. 28. C. laricinus. 



Leaves 1-2 mm. wide, 3-nerved; bracts lanceolate. 



29. C. pumilus. 

 Bracts strongly carinate and with conspicuous green tips. 



Brztcts acute; upper leaves not much reduced. 



30. C. elegans. 



