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. 358A 



Fig. 358B 



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



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



(A, drawings by Ada Hayden and Cliarlotte M. King; B, after HlUman, 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 oalled seed ; outer portions of achene blackish or 

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

 thick, short. In uncleaned clover seed. 



