150 FARM WEEDS OF CANADA 



GREAT RAGWEED {Ambrosia trifida L.) 



Other English names : Tall Ragweed, Crown weed, Kingweed, 

 Bitterweed. 



Native. Annual. A tall, coarse-branching plant, 4 to 8 

 feet high, with rough stems and leaves. Leaves pale green, 

 opposite, on long, margined footstalks, variable in shape, on 

 young plants deeply indented but scarcely lobed; as the stems 

 grow, 3 or even 5-lobed leaves are produced, but on many plants 

 leaves may be found without lobes. The male and female 

 flowers are borne in different heads on the same plant; the 

 male in long, slender spikes at the ends of the branches, and the 

 female 2 or 3 together, stalkless, in the axils of the leaves at the 

 base of the spikes. Male flowers 1/4 inch across, cup-shaped, 

 nodding; stamens yellow and conspicuous. Female flowers 

 inconspicuous; pistils slender and purplish. 



The seed (Plate 75, fig. 78) is about 1/4 inch long, brown, 

 urn-shaped, tipped with a tapering beak and bearing around 

 the base of this, about 1/3 from the top, 6 or 8 blunt spines, like 

 the points of a crown, which are the ends of more or less distinct 

 ribs. This crown-like appearance of the top of the seed has 

 suggested the names Kingweed and Crownweed, sometimes 

 used by millers. 



Time of flowering : July, seed ripe by the beginning of August. 



Propagation : By seeds, which are distributed in grain and 

 carried by water. Wheat from some districts of the West often 

 contains considerable quantities of Great Ragweed seed. 



Occurrence: Ontario and occasional in other eastern prov- 

 inces. Abundant in the rich Red River Valley in Manitoba 

 and extending westward mostly along the railways. 



