1014 CARDUACEAE 



gent spines and conspicuous dorsal glutinous ridges, the inner tapering into slender 

 tips; corollas rose or purple, rarely white. Cnicus undulatus megacephalus A. 

 Gray. Prairies and j)lains: N.D. — ]Mo. — Tex. — Colo. — Ida. Plain — Submont. 



C. FlodmaniiXmegacephalum. Intermediate between the two parent.s, leaves much 

 broader and with broader lobes, heads larger and bracts more glutinoas than in C. Flod- 

 manii. Colo. 



C. megacephalum X ochrocentrum. Leaves broad, resembling those of C. ochro- 

 centrum, but not decurrent and involucral bracts with short spines as in C. megacephalum. 

 Neb. — Kans. 



57. C. ochrocentrum A. Gray. Stem stout, 3-15 dm. high, tomentose; 

 leaves pinnatifid, with crowded, triangular segments and long, yellow spines, the 

 upper leaves usually conspicuously decurrent, white-tomentose beneath, floccose 

 above, greener but scarcely glabrate in age; heads 4-6 cm. high; bracts numerous, 

 lanceolate, with conspicuous broad glutinous ridges; spines yellow, stout; inner 

 bracts attenuate; corollas purple, rose, 'or rarely white. Carduus ochrocentrus 

 Greene. Plains: Neb. — Tex. — Ariz. Son. — Plain. Je-Au. 



58. C. arvense (L.) Scop. Perennial, with a horizontal rootstock, dioe- 

 cous; stems striate, 3-10 dm. high, branched above, hirsutulous or glabrous; 

 leaves sessUe, slightly clasping, or the lower petioled, green on both sides, gla- 

 brous or slightly pubescent, pinnatifid, with oblong, lanceolate or triangular 

 lobes; heads numerous, corymbose, about 2 cm. high; involucres of the staminate 

 heads hemispheric, those of the pistillate ones campanulate; corollas purple or 

 rarely white. Cnicus arvensis L. Carduus arvensis Robson. Canada Thlstle. 

 Fields, roadsides, and waste places: Newf. — Va. — Utah — B.C.; nat. from Eu. 

 Je-S. 



134. ONOPORDON (Vaill.) L. Cotton Thistle, Scotch Thistle. 



Coarse biennial or perennial herbs. Leaves alternate, lobed, spinescent, con- 

 spicuously decurrent on the stem. Heads discoid. Involucre globose; bracts 

 imbricate in many series, tipped with long spines. Receptacle flat, honej^-combed, 

 not bristly. Flowers all hermaphrodite and fertile. Corolla mostly purplish; 

 tube slender; throat dilated, and limb 5-cleft. Filaments pilose; anthers sagit- 

 tate at the base. Achenes 4-angled, oblong. Pappus of many plumose or bar- 

 bellate bristles, in several series, united at the base. 



1. O. Acantium L. Biennial: stem 1-3 m. high, white-tomentose, wing- 

 angled by the decurrent leaves; leaf-blades oblong, densely white-tomentose, with 

 triangular lobes, very spiny, the lower often 3 dm. long; heads 3-5 cm. broad; 

 bracts floccose and arachnoid-hairy, ending in short spines; flowers pale purple. 

 Waste places: N.S. — N.J. — Mich.; Utah — Colo.; native of Eurasia, cultivated 

 and escaped. Jl-S. 



135. CENTAUREA L. Blue Bottle, Cornflower, Bachelor's 



Buttons, Star Thistle. 



Perennial or annual herbs. Leaves alternate, entire or lobed. Heads dis- 

 coid. Involucres ovoid or globose, or urn-shaped; bracts imbricate in several 

 series, with appressed bases and spreading, lacerate, erose or spine-tipped ap- 

 pendages. Receptacle flat, densely bristly. Flowers all hermaphrodite and 

 fertile, or the marginal ones usually neutral, and with funnelform-dilated corollas. 

 Corolla of the fertile flowers purple, pink, yellow, or blue, with slender tube and 

 5-cleft limb. Anthers sagittate at the base. Style-branches short and obtuse. 

 Achenes compressed or obtusely 4-angled, obliquely attached, and crowned by a 

 disk or margin. Pappus of several series of bristles or palea, rarely wanting. 



Involucral bracts with lacerate broad appendages; flowers blue. 1. C. Cyanus. 



Involucral bracts with 3-5 spines; flowers yellow. 2. C. solslitialis. 



1. C. Cyanus L. Annual; stem 3-7 dm. high, with slender, ascending 

 branches, more or less floccose; leaves linear or linear-lanceolate, floccose, entire 

 or the lowest dentate or somewhat pinnatifid; heads long-peduncled ; involucres 

 round-urceolate, about 15 mm. high; bracts greenish yellow, with dark brown 

 fimbriate margins and tips; flowers blue, varying to rose or white. Waste places 



