430 



WEED FLORA OP IOWA 



Water Pepper {Polygonum hydropiper L.)- 



Achene lenticular, triangular; form broadly oblong or ovoid, 

 slightly gibbous; one-tenth in. in length; dull, color light. 



Mild Water Pepper {Polygonum hydropiperoides Mx.). 

 Achenes 3-angled, ovoid, angles between flattened, sides rounded, 

 one-eighth to one-tenth in. in length ; smooth, shining. 



Slender Pink Smartweed {Polygonum, lapathifoUum L.). 

 Achenes ovoid-oblong, lenticular, edges slightly angled along the 

 center, with a prominent remnant of the style at upper end, one- 



Figure 265A Figure 265B 



Pig. 265. A. Slender Pink Sniiartweed (.Polygonum lapathifoUum) . A, a side 

 view of an acliene bearing a part of the perianth at the base, enlarged. B, 

 a. group showing the natural size, one shown edgewise. C, a cross section 

 of an achene. 



B. Lady's Thumb iPolygonum perslcaria). A, B and C, side views of com- 

 mon forms of achenes ; C, a three-angled specimen. D, one covered by the 

 perianth (reduced from the size of A, B and C). B, a group showing the 

 natural size. F, a cross section of an achene. 



(After Hillman, Bull. Nev. Agr. Exp. Sta.) 



twelfth to one-tenth in. long; color light brown to dark brown, 

 shining; base of achene with remnant of perianth adhering. 



Pennsylvania Smartweed {Polygonum pennsylvanicum L.). 

 Achenes orbicular, usually broader than long, with edges as in 

 P lapathifoUum, remnant of style short, one-seventh to one-sixth 

 in. long; color blackish, dull, base of achene with perianth ad- 

 hering. 



Lady's Thumb {Polygonum persicaria L.). 



Achenes broadly ovate, lenticular, often somewhat 3-angled at 

 base, one-eleventh in. in length; surface smooth, shining; color 

 dark; remnant of perianth present at base. 



