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WEED FLORA OF IOWA 



Fig. 152-A. Distribution of Vervain. 



Distribution. — In damp situations in every county in .the state of 

 Iowa; also to the Atlantic coast and westward and southward. 



Extermination. — This weed, though abundant in low grounds, 

 seldom gives trouble where the field is drained and thorough culti- 

 vation is given. Spreads chiefly by the seed. 



Hoary Vervain (Verbena stricta Vent,). 



Description. — A soft, pubescent, perennial 1-3 ft. high; leaves 

 downy, ovate or oblong, serrate and sessile ; large blue flowers borne 

 in a dense sessile spike, 6 in.-l ft. long; trichomes several-celled, 

 thick-walled, pitted. 



The white vervain (V. urticaefolia) grows much taller than 

 V. stricta and has very small white flowers on elongated spikes. 

 It is a weed of thickets and waste grounds. 



Distribution. — In dry soil, prairies of Ohio to South Daktoa and 

 Wyoming, New Mexico and Texas. Commonly naturalized east- 

 ward. A common weed in every part of Iowa; frequent in pas- 

 tures. 



Extermination. — Easily destroyed by cultivation; rarely found 

 in cultivated fields for that reason. 



