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 plains: N.D. — Mo. — Tex. — Colo. — Ida. Plain — SubmonL 

 Je-S. 



C. FlodmaniiXmegacephalum. Tnterraediate between the two parents, leaves much 

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

 manii, Colo. 



C. megacephalumXochrocentrum. Leaves broad, resembluig those of C. ochro- 

 centrunu but not decurreiit and involucral bracts with short spines as in C. megacephalum. 

 Neb. — Kans. 



57. C. ochrocentrumA. Gray. Stem stout, 3-15 dm. hig;h, tomentose; 

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

 tipi3er leaves usually conspicuously decurrent, white-tomentose beneath, floccose 

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

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

 bracts attenuate; corollas piirple, rose, or rarely white. Carduus ochrocenlrus 

 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 sessile, 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 arvemis L. Carduiis arvensis Robson. Canada Thistle. 

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

 Je-S, 



r 



134. ONOPdRDON (^ aiU.) 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 

 nnbricate in many series, tipped with long spines. Receptacle flat, hone^^-combed, 

 not bristlv. 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 spmy, 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 niarginal ones usuaUy neutral, and with funneKorm-dilated corollas. 

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

 5-cleft lunb. 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. i n Cuanu^ 



Involucral bracts with 3-5 spines; flowers yeUow. 2. C. solstitialis. 



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

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

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

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

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



