268 American Midland Naturalist Monograph No. 2 



1. Leaves all pinnatifld or coarsely sinuate-dentate; plants annual. 



5. Rays conspicuous; bracts not black-tipped; fields, s. 111. May-June. [5. 

 lobatus Pers.] Butterweed S. glabettiis Poir. 



5. Rays none; bracts often black-tipped; cult, ground and waste places, occa- 

 sional; nat. from Eur. June-July. Groundsel S. vulgaris L. 



Tribe 11. Cynareae 



48. Arctium L. — Burdock 



1. Involucre 1-2 cm. broad; inner bracts not exceeding the €owers; heads race- 

 mose; petioles hollow, not deeply furrowed; waste places, common; nat. 

 from Eur. July-Sept. Common Burdock A. minus (Hill) Bernh. 



1. Involucre 2.5-3 cm. broad; inner bracts equalling or exceeding the flowers; 

 heads corymbose; petioles solid, deeply furrowed; waste places, occasional; 

 nat. from Eur. July-Oct. Great Burdock A. lappa L. 



49. EcHiNOPS L. — Globe-thistle 



E. sphaerocephalus L. Roadsides and waste places, occasional; introd. from 

 Eur. Apparently established in Kankakee Co., near Manteno, July 14, 1938, 

 Steyermark & Standley 1726. 



50. CiRSiUM Hill — Thistle 



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

 nial. 

 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 Thistle [C. lanceolatum (L.) Hill] .- 



C. vtilgare (Savi) Airy-Shaw 



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-tomentose beneath. 



4. Leaves pinnately parted into linear lobes, persistently white-tomen- 

 tose 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 III., common. Aug. -Sept 



Field Thistle C. discolor (Muhl.) Spreng 



5. Leaves merely toothed, or shal lowly 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, n 

 111., extending southw. to Kankakee, Peoria, and Adams counties 

 June-July. Hill's Thistle C. hillit (Canby) Fern 



