THISTLE FAMILY 1005 



Bracts narrow, with weak or slender spines. 



Bracts greenish, sometimes slightly arachnoid on the margins, but not 



floccose; lobes of the leaves obtuse. 25. C. oreophilum. 



Bracts slightly floccose when young; lobes of the leaves acute. 



Involucral spines more or less spreading; bracts yellowish; leaves 



slightly lobed. 15. C. nevadense. 



Involucra-1 spines ascending; bracts greenish; leaves deeply lobed. 



26. C. olivescens. 

 Inner bracts with conspicuous dilated, ovate or lanceolate, erose and twisted tips. 



Leaves not at all tomentose; heads usually solitary; corollas rose-purple. 



27. C. Drummondii. 

 Leaves more or less tomentose beneath; heads usually clustered; corollas white or 



pale rose. 

 Heads on short branches solitary in the axils of the leaves. 



28. C. magnificum. 

 Heads subsessile and clustered at the end of the stem. 



Plant more or less arachnoid as well as tomentose; leaves linear in outline. 



29. C. foliosum. 

 Plant not arachnoid, dark green; leaves broader. 30. C. lacerum. 



VIII. PULCHELLA. 



Leaves glabrous or at least glabrate in age. 



Spines of the middle bracts fully 1 cm. long and longer than the bracts. 



31. C. diffusum. 



Spines of the middle bracts 3-7 mm. long, shorter than the bracts. 

 Divisions of the leaves linear to triangular; involucre campanulate. 



Divisions of the leaves linear or linear-lanceolate, often again pinnatifld; 



leaves scarcely decurrent. 32. C. bipinnatum. 



Divisions of the leaves ovate or triangular; leaves conspicuously decurrent. 



33. C. calcareum. 

 Divisions of the leaves semi-orbicular, rounded-ovate; involucre hemispheric. 



34. C. lactucinum. 

 Leaves permanently tomentose, at least beneath. 



Tips of the inner bracts chartaceous, yellow, spreading, and slightly erose. 



35. C. spathulatum. 

 Tips of the inner bracts soft, erect and usually purplish. 



Spines of the middle bracts more than 1 cm. long, stout. 36. C. nidulum. 

 Spines of the middle bracts 3-6 mm. long, slender. 



Divisions of the leaves narrow; corolla rose-purple; involucre narrow. 



37. C. pulchellum. 



Divisions of the leaves broad and short, ovate; corollas crimson; involucre 

 broad. 38. C. arizonicum. 



IX. GRISEA. 

 Leaves green above, tomentose beneath; bracts not viscid. 



Bracts, with short spines, the outer not spinulose-ciliate. 35. C. spathulatum. 

 Bracts, with long spines. 



Spines of the bracts stout; heads 2.5-3 cm. broad. 39. C. griseum. 



Spines of the bracts slender; heads about 1.5 cm. broad. 40. C. modestum. 



Leaves loosely floccose on both sides; bracts decidedly viscid. 41. C. canovirens. 



X. UNDULATA. 

 Leaves white-tomentose beneath. 



Flowers ochroleucous. 



Involucral bracts very viscid, with broad glutinous dorsal ridge; divisions of the 



leaves rather few; spines of the bracts short. 

 Tips of the inner bracts more or less dilate and crisp; involucre of the terminal 



head 4-5 cm. in diameter. 42. C. plattense. 



Tips of the inner bracts linear-lanceolate, neither dilated nor crisp; heads 



usually less than 4 cm. in diameter. 



Bracts very numerous and small, with small spreading spines. 

 Stem-leaves deeply pinnately lobed, with rather stout spines. 



Lobes, at least of the lower leaves, oblong to rounded-ovate, obtuse. 



43. C. Nelsonii. 

 Lobes of the leaves lanceolate or linear-lanceolate, acute. 



Heads more than 3 cm. broad; bracts linear-lanceolate. 



44. C. palousense. 

 Heads less than 3 cm. broad; middle bracts ovate-lanceolate or 



ovate. 45. C. Tracyi. 



Stem-leaves sinuate-dentate or sinuately lobed, merely spinulose; 



heads 2.5-3 cm. broad. 46. C. nebraskense. 



Bracts comparatively few and broad, with erect spines; leaves sinuate- 

 ' dentate or slightly lobed. 47. C. brevifolium. 



Involucral bracts greenish or yellowish, scarcely viscid, with inconspicuous dorsal 

 ridge; divisions of the leaves numerous; spines of the bracts long and slender. 



48. C. acuatum. 



Flowers rose or purple, rarely white; dorsal viscid ridge not so prominent. 

 Involucres less than 4 cm. broad. 



Spines of the middle bracts 5-10 mm. long. 



Spines of the middle bracts slender and spreading. 48. C. acuatum. 



