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 tliin. glabrous. 



Leaves 2-3 cm. long, over 1 mm. wide, hght 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 tliicker. 



Leaves le.ss than 1 mm. wide: bracts glabrous. 10. C. albidux. 

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



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



11. C. coUinus. 

 Leaves 3-6 cm. long; Involucre somewhat viscid, merely arachnoid- 

 ciliate on the margin. 12. C. wyomingensis 



Hracts 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 tomen- 

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

 mm. long. 

 Bracts and mature leaves perfectly glabrous. 



Bracts ovate, 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 



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



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

 obtuse, about 0.5 nam. long, erect in age._ 



1 . . C. pinifolius. 

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



Inflorescence elongate-thyrsoid. IS. C. concolnr. 



Inflorescence corymbiform, flat or round-topped. 



Bracts lanceolate, acute; leaves le^s 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, linear-lanceolate, strongly cai-inate. 

 almost glabrous, except the erose-cUiate margins. 



21. C. pulcherritnus. 

 Bracts usually broader, more or less densely tomentose 



and viscid as weU as ciliate. 

 Stems equally leafy tliroughout; leaves all alike, 

 strongly ascending: bracts strongly cai-inate. 



22. C. frigidus. 

 Stems more leafy towards the ends; upper leaves 



much shorter; bracts sUghtly carinate. 



23. C. palUdus. 

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



tose on the back. 

 Bracts scarcely carinate; older branches not densely and 



thickly woolly. 24. C. speciosus. 



Bracts strongly carinate; older branches densely and thickly 

 woolly. 25. C. nauseosus. 



Bracts elUptical, 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 hispidulous-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, 1-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. puriilus. 

 Bracts strongly carinate and mth conspicuous green tips. 



Bracts acute; upper leaves not much reduced. 



30. C. elegans. 



