Northern Prairie Wildlife Research Center
Aquatic and Wetland Vascular Plants of the Northern Great Plains
49. Asteraceae, the Aster Family
15. Silphium L. -- Rosin-weed
1. 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).
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