208 COMPOSITAE 



1. A. mhius Schk. Burdock. 2°-6° high : leaves large, ovate cor- 

 date, more or less dentate and toraentose beneath : heads 6''-8'' broad. — 

 Common in waste places. July-October. 



46. CARDUUS L. 



Prickly herbs with alternate leaves and large terminal heads of purple 

 flowers. Involucral scales much imbricated, sharp-pointed. Pappug 

 plumose. 



Heads less than V broad. 

 Heads more than V broad. 

 Stems strongly wing-margined. 

 Stems not wing-margined. 



Leaves not white-tomentose above. 

 Leaves white-tomentose on both sides. 



1. C. arvensis (L.) Robs. Canada Thistle. Perennial by slender 

 rootstocks, l°-3° high : leaves oblong-lanceolate, siuuate-piunatifid, nearly 

 glabrous : heads dioecious : outer involucral scales appressed-tipped. — 

 Adventized in waste places near Brooklyn and 27th, Lydia and Inde- 

 pendence, and on South Troost, Kansas City, and at ShelVield. June- 

 July. 



2. C. lanceolatus L. CoJiMON Thistle. Biennial, 3°-5° high : 

 leaves sinuate-pinnatilid, woolly beneath : involucral scales tipped with 

 spreading sharp bristles —Commonly naturalized in fields. July-Sep- 

 tember. 



3. C. altissimus L. Tall Thistle. Biennial, 3°-10° tall : leaves 

 ovate-lanceolate, spinulosely dentate or rarely pinnatifid : outer involu- 

 cral scales sharp-tipped. — Abundant in thickets throughout. July-Oc- 

 tober. 



4. C. undulatus Nutt. Low Thistle. Biennial, 1°-4° high, woolly : 

 leaves oblong lanceolate, somewhat pinnatifid: outer involucral scales 

 sharp-pointed : heads large. — Adventized at Shelfield, Independence and 

 Glendale. July-September. 



47. CENTAUREA L. 

 Marginal flowers with enlarged corolla, neutral. Pappus of several 

 bristles. 



Plant floccose-pubescent above. 1. C. Ci/anus. 



Plant glabrate. 2. C. Americana. 



1. C. Cyanus L. Blue Bottle. Annual, l°-2° high : leaves linear- 

 lanceolate, entire : flowers bluish-purple, V broad.— Adventized around 

 Sibley and Independence. June-August. 



2. C. Americana Nutt. Star Thistle. Annual, l°-3° high : leaves 

 oblong-lanceolate, nearly entire : flowers pink-purple. 1^-2^' broad. — 

 Found as a waif between Dodson and Red Bridge. July-August. 



