Ambrosia 



COMPOSITAE 



961 



50 



Map2I05 



Ambrosia elatior L 



50 



Map 2107 



Xanthium spinosum L 



3. Ambrosia elatior L. (Ambrosia artemisii folia L. and Ambrosia 

 elatior var. artemisiifolia (L.) House.) (For a discussion of this species 

 see Jones. Studies on Ambrosia. Amer. Midland Nat. 17: 673-700. 1936 

 and Fernald & Griscom. Ambrosia artemisiaefolia and its variations in 

 temperate North America. Rhodora 37: 184-185. 1935.) Common Rag- 

 weed. Map 2105. I am referring all of our reports under whatever name 

 reported to this species. As Jones has pointed out, it is a highly variable 

 plant, producing pistillate plants and also plants bearing both stamens 

 and pistils. 



An abundant weed everywhere in cultivated and fallow fields, waste 

 places, roadsides, and almost any place where the ground is not covered 

 with a sod of grass. Milch cows are usually kept out of pastures and 

 stubble fields where it is abundant because when they eat this plant the 

 milk has a nauseating taste. 



The ragweeds are a few of the species whose pollen causes autumnal 

 hay fever. On account of the abundance of these plants they have the 

 credit of being the chief cause of this disease. 



N. S. to B. C, southw. to Va., Colo., and Wash. 



4. Ambrosia coronopifolia T. & G. (Ambrosia psilostachya of Gray, 

 Man., ed. 7 and Britton and Brown, Illus. Flora, ed. 2.) WESTERN Ragweed. 

 Map 2106. This is a western species that has been reported several times 

 in Indiana, probably mostly as a railroad migrant. It has been reported 

 from the dunes by Peattie and I have a specimen from near Hammond. 

 It has also been reported from Jefferson and Marion Counties, and from 

 the Lower Wabash Valley. In 1933 1 found it as a common weed in dry, 

 sandy soil along the C. E. & I. Railroad just south of Emison, Knox 

 County. It is common in sandy soil in a woods about 1 mile southeast 

 of Notre Dame, St. Joseph County (Nieuwland). Ek has found it in two 

 places along railroads in Howard County. 



Mich, to Sask., southw. to Idaho and n. Mexico; introduced into Conn. 



