Silphium trifoliatum L.
Family: Asteraceae
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Fibrous-rooted from a short rhizome or caudex; stem robust, (0.7-) 1-2 m, glabrous, often glaucous; lvs variously whorled or opposite or seldom alternate, entire or merely toothed, petiolate or tapering to a subpetiolar base; heads several to commonly ±numerous in an open infl, rather small, with ca 8 or ca 13 rays 1.5-3 cm, the disk ca 1-1.5(-2) cm wide; invol bracts glabrous except the ciliate margins; 2n=14. Open woods, prairies, and disturbed open places; se. Pa. to O. and Ind., s. to N.C., Ga., and Miss. Two vars.

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

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