f.00 



WEED FLORA OF IOWA 



Sow Thistle (Sonchus oleraceus L.). 



Achenes light brown, flattened, ribbed, the prominent ribs rough- 

 ened ; one-eighth in. long ; pappus of white capillary bristles, much 

 like the preceding. "Apt to occur among grass seeds." 



Wild Lettuce (Lactuca canadensis L.). 



Achene three-twentieths in. in length, straight or curved, sides 

 somewhat unequal, transversely wrinkled, blackish brown, beak one- 

 twentieth in. long, shorter than in L. floridana; one faint rib on each 

 side of prominent midrib ; decidedly convex on each side of midrib 

 to the flattened margin ; scar with whitish ring and small depression ; 

 pappus white, capillary. Much like L. floridana, beak smaller and 

 shorter. With commercial seed. 



Fig. 379A Fig. 379B 



Fig. 379. Seeds of Lettuce. A. Lactuca canadensis; a, enlarged achene, b, 



natural size. B. Lactuca floridana. 

 (A, after Hillman, Bull. Mich. Agr. Exp. Sta. ; B, drawing by Charlotte M. King.) 



False Lettuce (Lactuca floridana (L.) Gaertn.). 



Achene brown, transversely wrinkled, three-twentieths to seven- 

 fortieths in. in length, straight or slightly curved; beak light 

 brown, about one-fifth in. long, generally persistent, convex ; ribs 

 rather faint, 1 on each side of prominent midrib, strongly convex 

 on each side of midrib, margin flattened; pappus white, capillary. 



Prickly Lettuce (Lactuca scariola var. integrata Gren. & Godr.). 



Achenes brownish, margin somewhat lighter, surface roughened, 

 one-ninth to one-sixth in. long: beak one-tenth to one-eighth in. long, 

 lance-shaped, straight or slightly curved, upper end tapering 



