382 COMPOSITAE cARDUus 



or less compressed, attached by their very base. Pappus of co- 

 pious and rather rigid, long and plumous bristles in a single 

 series, connected at the very base into a ring, so that they remain 

 united after detaching. 



§ Perennials with comparatively small dioecious heads. 



C. ARVENSis Robs. Brit. Fl. 163. (Canada Thistle.) Stems 1-3 feet 

 high from creeping perennial rootstocks, corymbosely branching, usually 

 glabrate and green : leaves lanceolate, pinnatifid and toothed, furnished 

 with abundant weak prickles : heads loosely cymose, less than an inch 

 high, dioecious, in staminate plants ovate-globular with the flowers well 

 exserted : the pistillate oblong-campanulate, the flowers less exserted : 

 bracts of the involucre appressed, short, 'with very small weak prickly 

 points. A troublesome weed introduced from Europe : becoming too com- 

 mon in the Willamette Valley. 



§ 2 Biennials with the flowers all perfect. 



* Bracts of the involucre more or less unequal, all but the inner- 

 most terminating in subulate, spinose spreading appendages. 



C. LANCEOLATUS L. Sp. 821. (CoMMON THISTLE.) Stems stout, 2-4 feet 

 high, much branched: more or less villous-hirsute : leaves lanceolate, 

 deeply pinnatifid with lanceolate lobes, rigidly prickly, upper face strigose- 

 setulose; the base decurrent on the stem into interrupted prickly wings: 

 heads obovoid, 1-2 inches high, terminating the stems and branches: 

 bracts of the involucre arachnoid-woolly, lanceolate and mostly attefiuate 

 into slender spreading spines : corollas rose-purple. Pastures and waste 

 places throughout the northern United States. Naturalized from Europe. 



* * Bracts of the ovoid or hemispherical involucre appressed-imbri- 

 cate, the outer successively shorter, all with loose and dilated fimbri- 

 ate or lacerate white-scarious tips. 



C. Americanus Greene Proc. Philad. Acad. Stems rather slender, 2-4 

 feet high, branching above, the branches bearing solitary or scattered 

 naked heads, leaves white-tomentose beneath, lanceolate or broader, sin- 

 uately pinnatifid or some nearly dentate, others pinnately parted, weakly 

 prickly: heads erect, one inch high; principal bracts of the involucre 

 naked-edged or merely fimbriate-ciliate below, and the dilated scarious 

 apex as broad as long, fimbriate-lacerate, tipped with barely exserted cusp 

 or mucro ; innermost with lanceolate nearly entire scarious tips : flowers 

 ochroleucous : stronger pappus-bristles dilated-clavellate at tip. Willam- 

 ette Valley, Oregon to Colorado and New Mexico. 



* * * Bracts of the involucre mostly loose, not appressed-imbricate 

 nor rigid, tapering gradually from a narrow base to a slender prickly 

 muticose apex; outer not ver^ much shorter than the inner, wholly 

 destitute of dorsal glandular ridge or spot. 



■*" Some bracts of the involucre with scaiious or fringed tip or mar- 

 gins, at least the innermost slightly or not at all prickly-pointed: 

 leaves not decurrent on the stem, moderately prickly. 



C. remotifolius Hook. Fl. i, 302. Loosely arachnoid-woolly when 

 young : stems 2-8 feet high : leaves from sinuately to deeply pinnatifid, 

 more or less whitened by the loose tomentum beneath even in age: heads 

 12-18 lines high, pedunculate, scattered, naked or nearly so at base: in- 

 volucre lightly arachnoid and glabrate ; the bracts attenuate, the outer into 

 a weak small prickle ; the inner or some of them with a scarious entire or 

 sparingly lacerate tip : corollas ochroleucous, their lobes much shorter 

 than the throat : pappus of coarse bristles, the strongest with conspic- 



