COMPOSITAE 



COMPOSITE FAMILY 



ROSINWEED. COMPASS PLANT 



Silphium laciniatum L. 



All disk flowers of the plants in this genus are sterile. The 

 Compass Plant gets its name from the fact that its leaves have 

 a tendency to become twisted into a vertical plane with their 

 edges pointing north and 

 south. 



The Rosinweed or Com- 

 pass Plant is common on 

 prairies from Ohio to South 

 Dakota and south to Ala- 

 bama and Texas, blooming 

 from July to September. 



The stem is stout and 

 leafy and grows 6-12 feet 

 high. It and the leaves are 

 rough hairy. Basal leaves 

 are pinnatifid with oblong 

 or lanceolate lobes, long 

 petioled and often i foot or 

 more in length. Stem leaves 

 are alternate and mostly 

 sessile, gradually smaller 

 and less divided. 



The several to many 

 heads of yellow flowers are sometimes 5 inches broad. The 

 peduncles are bracted at the base. Only the 20-30 ray flowers 

 fruit. The akenes are oval, broadly winged, about one-half inch 

 long and notched at the end. The bracts of the involucre are 

 large, rigid and spreading at the tip. 



The Prairie Dock, Silphium terebinthinaceum Jacq., is also com- 

 mon on dry prairies. The stem is smooth or nearly so, 4-10 feet high 

 and leafless except at the base. The leaves, nearly all basal, are very 

 rigid and rough, ovate, mostly long petioled, pointed at the tip and 

 heart shaped at the base. They are often i foot long and 6 inches 

 wide. The heads are numerous, 2-3 inches broad and borne on smooth 

 peduncles. There are 12-20 ray flowers and both kinds of flowers are 

 yellow. The bracts of the hemispherical involucre are ovate-oblong, 

 erect and smooth or minutely hairy. The akenes are narrowly winged, 

 slightly notched at the end and 2-toothed. 



3S9 



