This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol3", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Silphium trifoliatum L. Sp. Pl. 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 glabrous beneath, entire or denticulate, 3'-7' long, 1/2'-1 1/2' wide; heads several or numerous, 1 1/2'-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, Virginia and Alabama. July-Oct.
Silphium Asteriscus L. Sp. Pl. 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'-5' long, 1/2'-1' wide; heads commonly few, 1'-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, south to Florida and Louisiana. June-Sept.
Silphium laciniatum L. Sp. Pl. 919. 1753.
Rough or hispid, very resinous; stem 6°-12° high; basal leaves pinnatifid or bipinnatifid, long-petioled, 1° long or more, the lobes oblong or lanceolate; stem leaves alternate, vertical, 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'-5' broad, the peduncles bracted at the base; rays 20-30, 1'-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.
Silphium terebinthinaceum Jacq. Hort. Vind. 1: pl. 43. 1770.
S. pinnatifidum Ell. Bot. S. C. & Ga. 2: 462. 1824.
Silphium terebinthinaceum pinnatifidum A. Gray, Man. 220. 1848.
Stem glabrous or nearly so, branched and scaly above, 4°-10° high. Leaves 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 dentate, laciniate or pinnatifid; heads numerous, 1 1/2'-3'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 emarginate at the apex.
On prairies and in dry woods, southern Ontario and Ohio to Minnesota, south to Georgia, Iowa and Louisiana. Rosin-plant. July-Sept.
5. compositum reniforme T. & G. Fl. N. A. 2: 276. 1842.
Stem scape-like, 3°-6° tall, glabrous or nearly so, corymbosely branched above. Leaves mostly basal, broadly ovate to reni-form, 4'-15' long, obtuse or abruptly pointed, coarsely dentate, deeply cordate at the base, long-petioled; heads numerous, about 1' broad, the peduncles glabrous; involucre campanulate, the bracts ovate or broadly oblong to narrowly oblong or oblong-spatu-late, obtuse; rays several, yellow; achenes suborbicular or orbicular-obovate, 3 1/2" long, the wings prolonged enough to form a shallow apical sinus.
In dry or stony soil, mountains of Virginia and North Carolina. July-Aug.
Silphium compositum Michx., a related southern species with pedately parted leaves, is reported as observed in southern Virginia.