268 American Midland Naturalist Monograph No. 7 



53. Echinops L. — Globe Thistle 

 E. sphaeroccphalus L. Roadsides and waste places, occasional; in- 

 trod. from Eur.; apparently established in Kankakee Co., near Man- 

 teno, July 14, 1938, Steyermark & Standley 1726; s. of Peotone, 

 Will Co., June 27, \952. H. E. A hies 6334. 



54. Cirsium Mill. — Thistle 



1. Heads large, more than 2 cm in diameter; flowers all perfect; 



plants biennial. 



2. Leaves bristly on the upper surface, grayish-arachnoid beneath, 



strongly decurrent; bracts of the involucre all spine-tipped; 



flowers violet-purple; fields, roadsides, and waste places, 



common; nat. from Eur. July-Aug. Bull Tliistle [C. lan- 



ceolatum (L. ) Hill] C. vulgare (Savi) Tenore 



2. Leaves not bristly on the upper surface; outer involucral bracts 

 spine-tipped, the inner acuminate, soft, or all the bracts 

 spineless. 

 3. Leaves white- torn en tose beneath. 



4. Leaves pinnately parted into linear lobes, persistently 

 white-tomentose on both sides; flowers cream-color; sand 

 dunes near Lake Michigan. June- July. Beach Thistle 



C. pitcheri (Torr.) T. & G. 



4. Leaves pinnately lobed or merely toothed. 



5. Leaves pinnately lobed, the margins revolute; rich soil 



along roads, in fields or in woods throughout 111. 



Aug.-Sept. Field Thistle .... C. discolor (Muhl.) Spreng. 



5. Leaves merely toothed, or shallowly lobed, the margins 



flat; woods, locally throughout 111. Aug.-Sept. Tall 



Thistle C. altissimum (L.) Spreng. 



3. Leaves not white-tomentose. 



6. Heads 5-10 cm broad; stem stout, 30-60 cm tall; bracts 

 spine-tipped and with a prominent glutinous midvein; 

 gravelly soil, extending southward to Coles, Sangamon, 

 and Adams counties. June-July. Hill's Thistle [C 



pumilum sensu auth., non (Nutt.) Spreng.] 



C. hillii (Canby) Fern. 



6. Heads 2-3 cm broad; stem 1-2.5 m tall; bracts without 



prickle-points; wet ground, chiefly in the northern half 



of 111., extending southward to Macoupin and Wabash 



counties. Aug.-Sept. Swamp Thistle....^, muticinn Michx. 



1. Heads smaller, 1.5-2.5 cm high and 1-1.5 cm in diameter; plants 



dioecious; perennials with spreading rhizomes. 



7. Leaves deeply pinnately lobed, strongly prickly; fields and 



waste places; nat. from Eur. June- Aug. Canada Thistle 



C. arvense (L.) Scop. 



7. Leaves almost entire or slightly lobed, weakly prickly; occa- 

 sional in fields and waste places; nat. from Eur. June- Aug. 



[C. arvense var. int. egri folium Wimm. & Grab.] 



C. setosum (Willd.) Bieb. 



