COMPOSITE FAMILY COMPOSITAE 
ENTIRE-LEAVED ROSINWEED 
Silphium integrifolium Michx. 
The,Entire-leaved Rosinweed is common on prairies from 
Ohio to Minnesota and south to Louisiana and Texas. The 
abundant resinous juices of this and related species are often 
used by children for chewing 
gum. : 
The plant is perennial and 
has a stout stem that is 
sometimes smooth and some- 
times rough hairy. It grows 
2-5 feet high and branches 
near the top. The leaves, us- 
ually entire but sometimes 
slightly toothed, are opposite, 
and because they are thick 
and rigid the plant is also 
called Stiff Rosinweed. Their 
form is ovate to ovate-lanceo- 
late, and they are rough 
above and hairy or smooth 
beneath. Those of the stem 
are closely sessile and often 
half-clasping by the rounded 
base. 
The heads of yellow flowers are quite numerous in August and 
september. The ray flowers are 15-25, pistillate and akene bear- 
ng. All but the inner bracts of the involucre are broad and have 
spreading leaflike tips. The receptacle is flat and chaffy. The 
akenes are flat oval or obovate, broadly winged and deeply 
1otched at the top. There is no pappus. 
The Cup Plant, Silphium perfoliatum L., grows in low moist 
places. The stem is square, stout and smooth and 4-8 feet high. The 
eaves are opposite, ovate and coarsely toothed, and the larger are 
)-12 inches long and 4-8 inches wide. The upper leaves are grown 
together by their bases, forming cup-shaped receptacles which are 
often partly filled with water and drowned insects. The heads are 
juite numerous and 2-3 inches broad. The 20-30 ray flowers are about 
| inch long. The akenes are winged and sometimes 2-toothed, 
360 
