208 COMPOSITAE 



1. A. minus Schk. BURDOCK. 2-6 high : leaves large, ovate cor- 

 date, more or less dentate and tomentose 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. Pappus 

 plumose. 



Heads less than V broad. 1. C. arvensis. 

 Heads more than V broad. 



Stems strongly wing-margined. 2. C. lanceolatus. 

 Stems not wing-margined. 



Leaves not white-torn en tose above. 3. C. altissimm. 



Leaves white-tomentose on both sides. 4. C. undulatus. 



1. C. arvensis (L.) Robs. CANADA THISTLE. Perennial by slender 

 rootstocks, l-3 high : leaves oblong-lanceolate, sinuate-pinnatifid, 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 Sheffield. June- 

 July. 



2. C. lanceolatus L. COMMON THISTLE. Biennial, 3-5 high : 

 leaves sinuate-pinnatifid, 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, l-4 high, woolly : 

 leaves oblong lanceolate, somewhat pinnatifid : outer involucral scales 

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

 Glendale. July-September. 



47. CENTAUREA L. 



Marginal flowers with enlarged corolla, neutral. Pappus of several 

 bristles. 



Plant floccose-pubescent above. 1. C. Cyanus. 



Plant glabrate. 2. C. Americana. 



1. C. Cyanus L. BLUE BOTTLE. Annual, l-2 high : leaves linear- 

 lanceolate, entire : flowers bluish-purple, l x 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. I'-SJ' broad. 

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



