Silphium Compositae 957 



Stem leafy throughout; large basal leaves wanting. 



Stems quadrangular; large plants with the upper leaves large and connate-perfoliate. 



2. S. perfoliatum. 



Stems more or less terete, the upper leaves not very large or connate. 



Leaves pinnately parted, large, all alternate; involucres generally 2-3 cm broad. 



Involucre and peduncle glandless 3. S. laciniatum. 



Involucre and peduncle glandular 3a. S. laciniatum var. Robinsonii. 



Leaves not parted or pinnatifid, entire, dentate or serrate, generally opposite or 



whorled or sometimes some of them alternate; involucres mostly 1-1.5 cm 



broad; involucral bracts ciliate. 



Outer involucral bracts glabrous on both faces; stems terete, glabrous and usually 



very glaucous; leaves lanceolate, oblong-lanceolate or lanceolate-ovate, 



opposite or usually the middle ones in 3's or 4's, tapering at the base into a 



distinct petiole except the upper ones which are sessile; petioles mostly 



0.3-3 cm long. 



Plant with at least the upper surface of the leaves pubescent; leaves chiefly 



verticillate though often opposite or alternate 4. S. trifoliatum. 



Plant glabrous; leaves usually opposite 4a. S. trifoliatum var. latifolhim. 



Outer involucral bracts more or less pubescent on one or both faces, sometimes 

 the whole involucre also glandular; stems more or less compressed to 4-sided, 

 usually somewhat scabrous or pubescent, rarely glabrous, but scabrous in the 

 inflorescence; leaves opposite, rarely a few ternate or alternate, ovate to 

 lanceolate-ovate, all sessile or the lower ones on very short petioles, narrowed, 

 rounded or cordate-clasping at the base. 



Involucral bracts pubescent but not glandular 5. S. integrifolium. 



Involucral bracts glandular-pubescent 5a. S. integrifolium var. Deamii. 



1. Silphium terebinthinaceum Jacq. Dock Rosin weed. Map 2094. 

 Found here and there in all parts of the state but frequent to common in 

 the prairie area. It has a very wide range of habitat — from the crest of a 

 wooded sandstone ridge to a marsh. It is generally found in a prairie 

 habitat along roadsides and railroads and rarely on open, wooded or gravel- 

 ly slopes. 



Ont. to Minn., southw. to Ga. and La. 



2. Silphium perfoliatum L. Cup Rosinweed. Map 2095. Found through- 

 out the state although it may be absent from a few of our northern coun- 

 ties. It is generally found on the alluvial banks of streams and on the low 

 borders of lakes. It is found both in woodland and in open places and 

 sometimes in low ground along roadsides. 



Mass. to Minn., southw. to Ga., Miss., and Okla. 



3. Silphium laciniatum L. Compassplant. Map 2096. This species is 

 a true prairie plant and in its distribution in Indiana it was restricted 

 to the prairie areas. All of our prairie areas are under cultivation and it is 

 found now only in moist prairie habitats along railroads and roadsides. 

 The published records extend its range somewhat beyond that shown on 

 the map. Beyond the area indicated by the map, it has been reported from 

 the area of Delaware, Jay, Randolph, and Wayne Counties, and from Elk- 

 hart, Knox, and Noble Counties. 



Ohio and Ind. to Minn., southw. to Okla. and Tex. 



