GENUS 51. 



THISTLE FAMILY 



3. Silphium trifoliatum L. Whorled 

 Rosin-weed. Fig. 4423. 



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 gla- 

 brous beneath, entire or denticulate, 3'-?' long, 

 V-ii' wide; heads several or numerous, \\'-2.' 

 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, Ontario, Vir- 

 ginia and Alabama. July-Oct. 



4. Silphium Asteriscus L. Starry Rosin- 

 weed. Fig. 4424. 

 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 petioles, dentate, or 

 the upper entire, 2'-$' long, i'-i' wide; heads 

 commonly few, i'-2' broad; rays 12-15; invo- 

 lucre 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, 

 south to Florida and Louisiana. June-Sept. 



5. Silphium laciniatum L. Compass- 

 plant. Pilot- weed. Fig. 4425. 



Silphium laciniatum L. Sp. PI. 919. 1753. 



Rough or hispid, very resinous ; stem 6-i2 

 high ; basal leaves pinnatifid or bipinnatifid, 

 long-petioled, i long or more, the lobes ob- 

 long or lanceolate; stem leaves alternate, ver- 

 tical, their edges tending to point north and 

 south, sessile, or the lower short-petioled, the 

 upper cordate-clasping at the base, gradually 

 smaller and less divided ; heads several or 

 numerous, sessile or short-peduncled, 2'-$' 

 broad, the peduncles bracted at the base ; rays 

 20-30, i '-2' long ; involucre nearly hemispheric, 

 its bracts large, rigid, lanceolate or ovate, very 

 squarrose ; achenes oval, about 6" long, the 

 wing broader above than below, notched at 

 the apex, awnless. 



On prairies, Ohio to South Dakota, south to 

 Alabama, Louisiana and Texas. Turpentine- weed, 

 polar-plant, rosin-weed. July-Sept. 



