482 



WEED FLORA OF IOWA 



Daisy Fleabane (Erigeron annuus (L.) Pers.). 



Achenes pale straw color, smooth, shining, flattened, obovate; 

 length 0.7-0.9 mm.; the apex bears a row of small straw -colored 

 bristles. 



Horseweed {Erigeron canadensis L.). 



Achenes one-twenty-fourth to one-twentieth in. long, white or 

 whitish, oblong lance-shaped, much flattened, one side often more 

 convex than the other; scar of seed with small, whitish, raised 



Fig. 355D 



Achenial hairs of Asters and Bigelovia. A. Aster laevis. B. Aster 

 macrophyllus. . C. Aster drummondii. D. Bigelovia nudata. 

 (Drawings by Mary A. Nichols and S. B. Fracker.) 



border, pubescent; pappus small, of numerous, fragile, capillary 

 bristles, usually breaking away. With grass seeds and lawn mix- 

 tures. 



Cup Plant (Silphium perfoliahim L.). 



Achenes large, two-fifths in. in length, dorsally flattened, 2- 

 winged, notched at apex, grayish or bronze-colored, margins thin. 



Marsh Elder (Iva xanthifolia Nutt.). 



Achenes obovoid, brown to black, with somewhat flattened longi- 

 tudinal faces 1.5 to 2 mm. in length, longitudinally striate with 

 fine markings. 



Small Ragweed (Ambrosia artemisiaefolia L.). 



Involucre containing a single achene one-twelfth to one-sixth in. 

 long, obovoid or globular, tipped by a tapering beak one-quarter 

 length of involucre; ridges several (4-10), prominent, with pro- 

 jecting tubercles, short, acute ; color grayish or brownish, pubescent ; 



