118 



WEED FLORA OF IOWA 



Distribution. — Common in every county in the state of Iowa and 

 east to northeast ; indigenous to the Rocky mountains. 



Extermination. — Easily exterminated by cultivation. 



Water Hemp (Acnida tuberculata Moq.). 



Description. — A tall, erect annual; leaves lanceolate to rhombic- 

 ovate, acute, or acutish; flowers dioecious; pistillate flowers small, 

 green, clustered in naked or leafy terminal and axillary spikes; 

 staminate flowers pale; dehiscent pericarp thin. 



The Acnida tamariscina (Nutt.) "Wood, of similar habit. Has 

 circumscissille fruit, otherwise like the A. tuberculata. 



Distribution. — Common along water courses, prairies and marshes 

 from northeast to Minnesota and Dakota. Found in Iowa in Story, 

 Boone, Polk, Pottawattamie, Woodbury, Emmet, Cerro Gordo, Clin- 

 ton, Linn, Marshall and Allamakee counties. 



Fig. 67. 



Water Hemp (.Acnida Uiberculata) . Common plant with yellowish 

 aspect. In old lake beds and prairies. 

 (Photographed by Colburn.) 



