ROSIN WEED (Compass Plant) 

 Silphium laciniatum L. 



July - September A giant on the prairies, the rosin weed grows in the 

 Prairie roadsides blazing hot sunshine of the Illinois summer. It is 



part of that picture which remains to tell of the old 

 prairie when plants like this one grew for miles and their resinous odor 

 filled the late summer air. 



Kosin weed is one of the giant Silphiums which still are guide-])Osts to 

 prairie conditions. Like the finger-posts of Spartina grass and Sullivant's 

 milkweed, the Silphiums, in particular the rosin weed and prairie dock, 

 indicate the presence of that dense black soil, unplowed and undisturbed 

 since the days when the prairie itself was unplowed and undisturbed. 

 The rosin weed gi-ows tall. It is seldom less than five feet tall and 

 often reaches twice that height. Its stout, densely liairy stem is tough 

 and resinous; globules of white resin ooze out and are sticky along the 

 stalk. The upper half of the stalk contains bright yellow sunflowers, two 

 to three inches broad with a calyx of overlapping haiiy, resinous bracts, 

 the flowers set alternately and spir;\lly around the stem. There may be 

 a dozen or two flowers all in Ifloom at once. Below tliem are the remark- 

 able leaves. They are thick, resinous, tough, so deeply lobed that they 

 almost appear compound. On the wide, open prairies the leaves of this 

 plant are often disposed so that they present their edges to north and 

 south, hence the name of compass plant by wliicli it is commonly called. 



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