766 



MANUAL OF POISONOUS PLANTS 



staminate borne in spikes surrounded by the larger bract-like leaves; the in- 

 volucre is turbinate to ovoid, S-7-ribbed, beaked, each rib bearing a tubercle 

 near the summit; the involucre enclosing a single achene. 



Distribution. The greater ragweed is distributed from Quebec to Florida 

 throughout the Atlantic region to Texas, common throughout the Mississippi 

 Valley west to Colorado and Northwest Territory, in Manitoba and Saskatch- 

 ewan. 



Fig. 444. Small Ragweed (Ambrosia arte- 

 misiifolia). In the lower left hand corner is a 

 bur that contains the seed; upper right hand 

 Fig. 443. Tall TZgvfeed (Ambrosia triUda). corner, a flower; in middle, branch and leaf. 

 (U. S. Dept. Agr.) Probably poisonous. (Ilolm-Britton). 



Ambrosia artemisiifolia L. Hogweed. Bitterweed 



A puberulent or hirsute branched annual 1-3 feet high; leaves thin, once to 

 twice pinnatifid; the upper alternate, the lower usually opposite, pale or canescent 

 beneath; flowers monoecious, the staminate above and the pistillate in the lower 

 axils of the leaves; the fertile heads are obovoid or globose, short beaked 

 and 4-6 spined. 



Distribution. A troublesome weed in northern states. Its distribution in 

 North America is from Nova Scotia to Florida throughout the Atlantic states 

 and Mississippi Valley; in the Rocky Mountain region and west to British 

 Columbia; also in Mexico and the West Indies and South America. 



Poisonous properties. The greater ragweed is regarded as especially 



