484 



WEED FLORA OF IOWA 



"Western Ragweed {Ambrosia psilostachya DC). 



Bur teretish, one-eighth to one-fifth in. long, obovoid, with beak 

 less prominent than in preceding species; tubercles when present, 

 short ; ridges 4-5 ; color grayish ; pubescent ; involucre pitted, readily- 

 removed leaving brown achenium, with short beak ; cotyledons large, 

 fleshy, oily. In clover seed. 



Large Ragweed (Ambrosia trifida L.). 



Achene one-fifth to three-tenths in. in length, one-sixth in. across 

 at widest portion near upper end, containing seed one-fifth to three- 

 tenths in. long, or in extreme cases nearly one-half in. ; width at 

 upper end 1.6 in., involucre obovate, narrow below, gradually 

 widening toward top, tipped by tapering beak; fruit prominently 



Fig. 358 A 



Fig. 358B 



Fig. 358. A. White-leaved Franseria (Franseria discolor). B. Franseria 



Hookeriana. A, bur enlarged ; B, natural size ; C, bur cut lengthwise. 

 (A, drawings by Ada Hayden and Charlotte M. King; B, after Hillman, Bull. 



Nev. Agr. Exp. Sta.) 



ridged, forming rather long projecting tubercles, 4-10 in number, 

 near upper end; involucre pitted or marked by cross ridges; color 

 grayish or brownish ; pubescent or nearly smooth ; encloses a single 

 achene, commonly called seed ; outer portions of achene blackish or 

 brownish; embryo with large thick cotyledons; seed oily, cauliele 

 thick, short. In uncleaned clover seed. 



