CHAPTER XXII 



POLYGONACE^ (Buckwheat Family) 



Herbaceous representatives of this family are largely found 

 in temperate regions, tree- 

 like species in Anierican 

 tropics, while shrubby ones 

 are limited to western Asia. 

 There are about 30 genera 

 and 800 species. Rhubarb 

 and buckwheat are the prin- 

 cipal cultivated members, 

 while a number of species of 

 Rumex (dock) , and of Polygo- 

 num (knotweed, bind-weed, 

 etc.) are bad weeds. 



Stems.— The stems are 

 conspicuously jointed and 

 usually swollen at the joints. 

 The leaves are alternate 

 (Fagopyrum), opposite {Ma- 

 counastrum) , or whorled 

 (mountain sorrel, Oxyria 

 digyna). They are mostly 

 entire, rarely lobed or divided. 

 The stipules, with a few ex- 

 ception s, are membranous, 

 sheathing, and united to 



form a very characteristic structure, the ocrea (plu. ocreae) 



(Fig. no). 



284 



Fig. 1 10. — Leaf of common buckwheat 

 (Fagopyrum vulgare). X i. 



