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 1 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 1 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. 
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