170 FARM WEEDS OF CANADA 



PERENNIAL SO V THISTLE {Sonchus arvmsis L.) 



Other English names: Field Sow Thistle, Creeping Sow 

 Thistle, Corn Sow Thistle (in England), also sometimes incorrectly 

 called Russian Ihistle, which, however, is an entirely different 

 plant, described in the Spinach family. 



Introduced from Europe. Perennial, deep-rooted, with 

 large and vigorous running rootstocks. Stems 1 to 5 feet high, 

 hollow, simple, with few leaves, and branching at the top. Whole 

 plant filled with a bitter, milky juice. Leaves 6 to 12 inches 

 long, pointed, deeply cut, the lower divisions directed backward, 

 clasping the stem by their heart-shaped base, and edged with 

 soft spines. Flowers bright yellow, 1^ inches across, in corymbs, 

 closing in strong sunlight; the flower stalk and the scaly bracts 

 surrounding the flower-heads bristly, covered, 'n the common 

 form, with long, glandular hairs. A perfectly smooth variety 

 is common in parts of New Brunswick and also occurs at Port 

 Hope, Ontario. 



The seed (Plate 76, fig. 94) is about 1/8 inch long, dark reddish- 

 brown, oblong, closely and deeply ridged lengthwise, the ribs 

 wrinkled transversely, giving the seed the appearance of being 

 ridged both ways, bearing at the top a tuft of white, silky and 

 persistent hairs which spread in drying and enable the seed 

 to be carried long distances by the wind. 



Time of flowering: June to August; seed ripe by July. 



Propagation: Very rapid, by seeds and running rootstocks. 



Occurrence: Abundant in cultivated fields and along road- 

 sides, rapidly spreading from the Atlantic Coast to Manitoba; 

 introduced in a few localities from there westward. 



Injury: Perennial Sow Thistle, from its exceptionally 

 vigorous running rootstocks and the large amount of seed it 

 matures, is one of our most aggressive weed enemies. It causes 

 enormous loss, both on account of the difficulty of eradicating 

 it and by reducing crop yields. Wherever established, it chokes 



