BUCKWHEAT FAMILY 57 



2. Flowers in several to many axillary or terminal 

 racemes or clusters 



a. Flowers in large axillary and terminal racemes 



(1) Stems twining or trailing; leaves ovate- 



arrow-shaped or heart-shaped ; bindweeds 



(a) Leaves ovate to lance-arrow-shaped; 



stems .5-4 ft. long; sepals not winged 



in fruit P. convolvulus 



(b) Leaves ovate-heart-shaped; stems 3-10 



ft. long ; sepals broadly winged in fruit P. scdndens 



(2) Stems erect, not twining; leaves not ar- 



row-shaped, or heart-shaped 



(a) Papery sheaths at the swollen stem joints 



fringed with bristles 

 x. Racemes erect 



(x) Racemes oblong, dense P. persicdria 



(y) Racemes cylindric, narrow, often 



interrupted 



m. Sepals covered with waxy dots P. punctdtum 

 n. Sepals without waxy dots P. hydropiperoides 



y. Racemes nodding ; flowers greenish ; 



juice sharp P. hydro piper 



(b) Papery sheaths not fringed with bristles 

 x. Racemes nodding, lance-cylindric, nar- 

 row ; stamens 6 P. I apathi folium 



y. Racemes erect, oblong, broad; stamens 



usually 8 P.pennsilvdnicum 



b. Flowers mostly in small axillary clusters, the 



ends of the branches in some raceme-like; 

 knotweeds 



(1) Clusters all axillary, the stems leafy 



throughout 



(a) Plants prostrate, or nearly so; leaves 



small; stamens mostly 8 P.aviculdre 



(b) Plants erect; leaves large; stamens 5-6 P. erectum 



(2) Clusters axillary, but the upper leaves in- 



conspicuous 



(a) Flowers and fruits erect 

 x. Achenes projecting beyond the calyx 



for half its length or more P. exsertum 



