CLASSIFICATION OF ANGIOSPERMS. 525 



dark brown, cordate-winged, 3-angled akene. The dried root is 

 somewhat fusiform, reddish-brown, and with a bitter, astringent 



FIG. 291. Polygonum Pennsylvanicum (Fam. Polygonaceae), one of about 30 species 

 of knotweeds, being common in waste places, all herbaceous, and characterized by the leaves 

 having sheathing stipules. Typical of this group is P. Pennsylvanicum, having lanceolate 

 leaves and short, erect terminal spikes with bright rose-colored flowers. After Brown. 



taste. It contains chrysophanic acid, tannin, calcium oxalate, and 

 some of the other constituents found in rhubarb (Fig. 289). 



Rume.r Acetosella (field or sheep sorrel) is a slender annual 

 herb with hastate leaves, having flowers in compound racemes. 



