Aquatic and Wetland Vascular Plants of the Northern Great Plains
49. Asteraceae, the Aster Family
15. Silphium L. -- Rosin-weed1. Silphium perfoliatum L. -- Cup plant
Stout, erect, rhizomatous perennial 8-20 dm tall; stem square, glabrous. Leaves simple, opposite, at least the upper ones connate-perfoliate, forming a cup around the stem, the lower leaves often short-petioled and connate by wings on the petioles, the blades ovate to deltate, 7-30 cm long, 3-15 cm wide, scabrous above, scabrous to hispidulous beneath, acute, coarsely toothed. Heads several to many in an open inflorescence, the disk 1.5-2.5 cm across; involucre 12-25 mm high, the bracts broadly ovate to elliptic, subequal, acute to obtuse, ciliolate on the margins; receptacle flat, chaffy, the outer bracts on the disk spatulate, transitional to narrower, more linear bracts inward; ray florets 20-30, pistillate, the ligules yellow, 1.5-2.5 cm long, the ovaries imbricate in 2-3 series, their styles branched, papillose; disk florets functionally male, their corollas pale to yellowish, their styles undivided, puberulent. Achenes flat, obovate, narrowly winged, 8-10 mm long, 5-6 mm wide; pappus none. Jul--Aug. River bottoms and swampy places; occasional from e ND, s to e NE; (s Ont. to ND, s to GA and LA).
Previous Section -- Senecio pseudaureus Rydb.
Return to Family -- Asteraceae - The Aster Family
Next Section -- Solidago gigantea Ait. -- Late goldenrod
