Genus 50.] 



THISTLE FAMILY. 



407 



2. Silphium integrifdlium Michx. 

 Entire-leaved Rosin-weed. (Fig. 3866.) 



Silphium inlegrifolium Michx. Fl. Bor. Am. 2: 146. 



1803. 



Stem glabrous, rough or sometimes hirsute, 

 oorynibosely branched above, 2-5 high. Leaves 

 ovate to ovate-lanceolate, acute or acuminate, en- 

 tire, denticulate or remotely dentate, rough above, 

 pubescent or glabrous beneath, those of the stem 

 all closely sessile, often half-clasping but not con- 

 nate-perfoliate at the rounded base, 3 / -5 / long, 

 i / -2 / wide; heads usually numerous, i / -2 / broad; 

 involucre nearly hemispheric, its outer bracts 

 ovate or ovate-lanceolate, acute, spreading, cilio- 

 late or pubescent; rays 15-25; achenes oval or 

 obovate, 4 // ~5 // long, deeply emarginate. 



On prairies, Ohio to Minnesota, south to Louisiana, 

 Nebraska, Arkansas and Texas. Aug.-Sept. 



3. Silphium trifoliatum L. Whorled 

 Rosin-weed. (Fig. 3867.) 



Silphium trifoliatum L. Sp. PI. 920. 1753. 



Stem glabrous.sometimes glaucous, corym- 

 bosely branched at the summit, 4-7 high. 

 Leaves lanceolate or oblong-lanceolate, the 

 middle ones almost always whorled in 3's or 

 4's, acuminate at the apex, narrowed at the 

 base and usually somewhat petioled, rough 

 or roughish above, pubescent or nearly glab- 

 rous beneath, entire or denticulate, 3 '-7' long, 

 Yz'-iYz' wide; heads several or numerous, 

 \)/ z '-2 f broad; involucre hemispheric, its 

 outer bracts ovate or oval, acute or obtuse, 

 glabrous, or slightly pubescent.ciliolate; rays 

 15-20; achenes oval or obovate, narrowly 

 winged, emarginate, sharply 2-toothed. 



In woods, Pennsylvania to Ohio, south to Vir- 

 ginia and Alabama. July-Oct. 



4. Silphium Asteriscus L,. Starry 

 Rosin-weed. (Fig. 3868.) 



Silphium Asteriscus L. Sp. PI. 920. 1753. 



Stem hispid-pubescent, simple, or branched 

 above, 2-4 high, usually purple. Leaves 

 nearly all alternate, ovate, ovate-oblong, or 

 lanceolate, acute or obtusish, sessile, somewhat 

 clasping, or the lower narrowed into short peti- 

 oles, dentate, or the upper entire, 2 / -5 / long, 

 Yz'-\ f wide; heads commonly few, i / -2 / broad; 

 rays 12-15; involucre hemispheric, its bracts 

 mostly hispid, ovate to oblong, acute or obtuse, 

 squarrose; achenes oval or obovate, narrowly 

 winged, 2-toothed. 



In dry soil, Maryland to Tennessee and Missouri, 

 rsouth to Florida and Louisiana. June-Sept. 



