4o8 



COMPOSITAR. 



[Vol. III. 



6. Silphium terebinthinaceum 



Jacq. Prairie Dock. Prairie 

 Burdock. (Fig. 3870.) 



Silphium terebinthinac€Uin Jacq. Hort. 

 Vind. I: pi. 4j. 1770. 



Stem glabrous or nearly so, branched 

 and scaly above, 4°-io° high. I.,eaves 

 all basal or nearly so, coriaceous, ovate, 

 mostly long-petioled, acute at the apex, 

 cordate at the base, rough on both sides, 

 often 12' long and 6' wide, sharply den- 

 tate; heads numerous, 'iVz'-Z' broad, 

 borne on glabrous peduncles; involucre 

 hemispheric, its bracts ovate-oblong, 

 erect, glabrous or minutely pubescent; 

 rays 12-20; achenes obovate, narrowly 

 •winged, slightly 2-toothed and emargin- 

 ate at the apex. 



(^n prairies and in dry woods, southern 

 Ontario and Ohio to Minnesota, south to 

 Georgia, Iowa and Louisiana. Called also 

 Rosin-piant. July-Sept. 



Silphium terebinthinaceum pinnatifidum (Kll.) 



A. Gray, Man. 220. 1S4S. 

 S. pinnalifidum Ell. Bot. S. C. & Ga. 2: 462. 



1824. 



Leaves laciniate or pinnatifid. Ohio to 

 Georgia. 



5. Silphium laciniatum L. Com- 

 pass-plant. Pilot-weed. 

 (Fig. 3869.) 



Silphium lacinialum L. Sp. PI. 919. 1753, 



Rough or hispid, very resinous; stem 

 6''-l2° high; basal leaves pinnatifid or bi- 

 pinnatifid, long-petioled, 1° long or more, 

 the lobes oblong or lanceolate; stem leaves 

 alternate, vertical, their edges lending 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, ses- 

 sile 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 

 Alabatna, Louisiana and Te.xas. Called also 

 Turpentine-weed, Polar-plant, Rosin-weed. 

 July-Sept. 



51. CHRYSOGONUM L. Sp. PI. 920. 1753. 



Pubescent perennial herbs, with opposite and basal petioled leaves, and sleuder-peduncled- 

 axillary and terminal, rather large heads of both tubular and radiate, yellow flowers. In 

 volucre hemispheric, its bracts in 2 series of 5, the outer large, obovate or spatulate, folia- 

 ceous, the inner oval, firm, each subtending a pistillate ray-flower. Receptacle chafl"y, each 

 scale subtending and partly enclosing a perfect but sterile tubular flower with a 5-toothed 

 corolla. Anthers nearly entire at the base. Achenes obovate, compressed, their margins- 

 acute, not winged, i-nerved on the back, 1-2-ribbed on the iuner side. Pappus a short half- 

 cup-shaped crown. [Greek, golden-knee.] 



A raonotypic genus of eastern North America. 



