768 



MANUAL OF POISONOUS PLANTS 



Distribution. Common in waste grounds from Ontario to Missouri and 

 Texas to Florida. Native to the old world. 



Fig. 445. Thorny Clot-bur (Xanthium 

 sfinosum). After Hochstein. 



Xanthium Strumarium h. 



A low, rough, branching annual from 1-2 feet high; leaves slender, petioled, 

 broadly ovate or orbicular, 3-5-lobed, both surfaces rough; bur oblong, smooth 

 or nearly so, with two straight or nearly straight beaks. 



Distribution. In waste places along the Atlantic seacoast. Native to 

 Europe. 



Xanthium canadense Mill. Cockle Bur 



A coarse rough annual from 1-3 feet high, stem marked with brown punct- 

 ate spots; leaves alternate, cordate or ovate, 3-nerved, long petioled; flow- 

 ers monoecious, staminate and pistillate flowers in diff^erent heads, the pistillate 

 flowers clustered below ; the involucre of the staminate flowers somewhat 

 flattish of separate scales, receptacles cylindrical; scales of the fertile involucre 

 closed in fruit, 2-beaked, containing 2 achenes ; the bur is densely prickly 

 and hispid, achenes oblong without pappus. 



Distribution. In Iowa this species is very common along the sandy bottoms 

 of our streams and river courses. It is less troublesome in uplands but here 

 and there it does occasion some trouble even in the central and southern part 

 of the state. However, in southern and southeastern Iowa the weed is often 

 quite troublesome in cornfields, coming up in enormous quantities. In Texas, 

 too, it appears in the very richest soil. Its distribution in North America is 



