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..
Tall perennial herbs, with resinous juice, opposite whorled or alternate leaves, and large corymbose or paniculate (rarely solitary) peduncled heads of both tubular and radiate yellow flowers. Involucre hemispheric or campanulate, its bracts imbricated in few series. Receptacle flat or nearly so, chaffy, the chaff subtending the disk-flowers. Ray-flowers in 2 or 3 series, pistillate, fertile, the ligules numerous, linear. Disk-flowers perfect but sterile, their corollas tubular, 5-toothed, the style undivided. Anthers minutely 2-toothed or entire at the base. Achenes broad, dorsally flattened, 2-winged, notched at the apex. Pappus none, or of 2 awns confluent with the wings of the achene. [Greek, from the resinous juice.]
About 12 species, natives of North America, known as Rosin-weed or Rosin-plant. Type species: Silphium Asteriscus L.
Stem leafy, the leaves opposite, alternate, or verticillate.
Leaves, or their petiole-bases, connate-perfoliate: stem square.
1. S. perfoliatum.
Leaves not connate-perfoliate, sessile or petioled.
Leaves opposite, or the uppermost alternate; cauline sessile.
2. S. integrifolium.
Leaves, or some of them, verticillate in 3' s or 4' s, petioled.
3. S. trifoliatum.
Most or all of the leaves alternate, entire or dentate.
4. S. Asteriscus.
Leaves all alternate, pinnatifid or bipinnatifid, large.
5. S. laciniatum.
Stem leafless or nearly so, scaly above; leaves basal, large. Leaves sharply serrate to pinnatifid; achenes obovate.
6. S. terebin hinaceum.
Leaves coarsely dentate; achenes suborbicular.
7. S. reniforme.
S. perfoliatum L. Sp. Pl. Ed. 2, 1301. 1763.
Stem square, glabrous, or rarely somewhat hispid, branched above, or sometimes simple, 4°-8° high. Leaves ovate or deltoid-ovate, opposite, the upper connate-perfoliate, the lower abruptly contracted into margined petioles, all thin, usually scabrous on both sides, or pubescent beneath, coarsely angulate-dentate, or the upper entire, the larger 6-12' long, 4'-8' wide; heads commonly numerous, 2'-3' broad; rays 20-30, about 1' long and 2" wide; involucre depressed-hemispheric, its outer bracts broad, ovate, ciliolate, spreading or erect; achenes obovate, emarginate, sometimes 2-toothed.
In moist soil, southern Ontario to Minnesota, South Dakota, New Jersey, Georgia, Nebraska and Louisiana. Naturalized near New York City, and elsewhere escaped from cultivation. Called also ragged-cup. July-Sept.
S. integrifolium Michx. Fl. Bor. Am. 2: 146. 1803.
Stem glabrous, rough or sometimes hirsute, co-rymbosely branched above, 2°-5° high. Leaves ovate to ovate-lanceolate, acute or acuminate, entire, denticulate or remotely dentate, rough above, pubescent or glabrous beneath, those of the stem all closely sessile, often half-clasping but not connate-perfoliate at the rounded base, 3'-5' long, 1'-2' wide; heads usually numerous, 1'-2' broad; involucre nearly hemispheric, its outer bracts ovate or ovate-lanceolate, acute, spreading, ciliolate 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.