332 



WEED FLORA OF IOWA 



Pig. 192. Perennial Ragweed (Ambrosia psilostachya) . 



roadsides. 

 (Photographed by Quade.) 



Pastures, drift soils. 



Marsh Elder {Iva xanthifolia Nutt.). 



Description. — An annual 1-8 ft. high; stem frequently pubescent 

 when young ; leaves opposite, rhombic, ovate, or lowest heart-shaped, 

 doubly serrate, or cut-toothed, obscurely lobed; upper surface 

 minutely scabrous, caneseent beneath, especially when young; 

 petiole frequently ciliate at its upper end ; flowers borne in spikelike 

 clusters forming a compound panicle ; heads small, crowded ; outer 

 bracts of the involucre broadly ovate, greenish; inner membrana- 

 ceous; achenes glabrate. This plant is also known botanieally as 

 Cyclachaena xanthifolia Fr. 



Distribution. — Common in the eastern Eockies, to Saskatchewan 

 and western "Wisconsin, most abundant in Iowa along Missouri 

 river where it is troublesome in fields, along highways, and in 



