THISTLE FAMILY 1009 



spines; heads subsessile, clustered on the crown, 2.5-3 cm. high; bracts glabrous, 

 lanceolate, the outer successively shorter and tipped with usually short spines, 

 the inner with lanceolate, slightly erose and twisted tips; corollas pinkish or 

 white. Cnicus Drummondii acaulescens A. Gray. Carduus acaulescens Rydb' 

 Carduus americanus Rydb., not Greene, Carduus longissimus Heller, and Cir- 

 sium americanum K. Schum. represent a form with long-spined involucral 

 bracts. Mountains: Colo. Utah Wyo. Submont. Mont. Je-Au. 



23. C. coloradense (Rydb.) Cockerell. Stem rather stout, simple, 3-5 dm. 

 high, striate, sparingly arachnoid; leaves 1.5-2 dm. long, pinnately lobed about 

 half-way to the midrib, sparingly arachnoid or glabrous above, more or less 

 white-tomentose beneath; lobes ovate, tipped with yellowish spines, 2-5 mm. 

 long; heads usually scattered, 3-4 cm. high and about as broad; bracts glabrous 

 or nearly so, firm, the outer with weak spines, the inner unarmed; corolla white 

 or slightly pinkish. Carduus coloradensis Rydb. Cnicus Drummondii A. Gray, 

 in part. C. scariosus A. Gray, in part. Mountains: Colo. Utah. Submont. 

 Mont. Jl-Au. 



C. acaulescens X coloradense. Intermediate between the two parents, usually 

 short-stemmed with small heads, in a flat-topped terminal cluster. Colo. Utah. 



C. coloradense X undulatum. Resembling C. undulatum in the red flowers, though 

 paler, in the bracts which have a glandular ridge, though less distinct, and in the leaf- 

 form; and approaching C. coloradense in the habit and the form of the bracts, the inner- 

 most of which have lanceolate twisted tips. Colo. 



24. C. Butleri Rydb. Stem angled, purple, sparingly arachnoid-hairy, very 

 leafy, 6-10 dm. high or more; leaves linear-oblanceolate or linear, almost entire 

 or sinuately lobed, spinulose-ciliate, and if lobed the short lobes ending in slightly 

 stronger spines, green and sparingly arachnoid above, grayish tomentose beneath ; 

 heads few, scattered, leafy-bracted, hemispheric, about 4 cm. high, 45 cm. wide; 

 outer bracts lanceolate, brownish, glabrous or nearly so, ending in short weak 

 spines 2-3 mm. long, the innermost linear-lanceolate, attenuate; corollas pinkish. 

 Carduus Butleri Rydb. Valleys: Mont. Jl-Au. 



25. C. oreophilum Rydb. Stem 4-8 dm. high, stout, angled; basal leaves 

 about 2 dm. long, thin, light green and glabrate above, more or less grayish 

 tomentose beneath, pinnately lobed; lobes triangular, usually 2-3-lobed, with 

 slender spines 3-10 mm. long; heads hemispheric, 2-2.5 cm. high; outer bracts 

 tipped with flat spines, 3-6 mm. long. Carduus oreophilus Rydb. Cirsium 

 eriophilumK. Schum. Wooded valleys: Colo. Utah. Submont. Subalp. Jl-Au. 



C. oreophilum Xscopulorum. Resembling C. scopulorum in the heads crowded at 

 the ends of the stem, the arachnoid involucres, and general habit; but the leaves are 

 broader, the involucral bracts broader at the base, and the flower-cluster not nodding; 

 differing from C. oreophilum in its less deeply dissected leaves and more arachnoid inflor- 

 escence. Colo. 



C. acaulescens X scopulorum. Resembling C. acaulescensin leaf-form and pubescence, 

 in the small and clustered heads, but is usually leafy-stemmed and has arachnoid invo- 

 lucres. Colo. 



C. foliosum X scopulorum. This has the habit and bracts of Cirsium foliosum, but 

 the involucre is densely arachnoid as in C. scopulorum and the leaves have more numer- 

 ous and crowded lobes. Wyo. 



C. griseum X scopulorum. With the habit, leaf-form and long flat involucral spines 

 of C. griseum, but inflorescence arachnoid-hairy and leaf-segments more numerous. 

 Carduus Osterhoutii Rydb. Colo. 



26. C. olivescens Rydb. Stem slender, somewhat tinged with purple, more 

 or less floccose, 4-8 dm. high; leaves linear in outline, 1-2 dm. long, densely 

 white-tomentose beneath, loosely floccose above, deeply pinnatifid, with numer- 

 ous lanceolate, often 2- or 3-cleft lobes, ending in short yellow spines; heads few, 

 peduncled, about 3 cm. high, 3-3.5 cm. wide; bracts slightly floccose on the mar- 

 gins, light olive-colored, ending in yellow spines 2-4 mm. long, or the innermost 

 innocuous; corollas straw-colored. Carduus olivescens Rydb. Tablelands: Utah. 

 Mont. Au. 



27. C. Drummondii T. & G. Stem low, 1-3 dm. high, slightly arachnoid- 

 hairy; leaves oblanceolate, in outline, green, somewhat arachnoid, but not at all 



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