Silphium perfoliatum

Plants caulescent, 75-300 cm; fibrous rooted. Stems square, glabrous, hispid, or scabrous. Leaves: basal caducous; cauline usually opposite, rarely whorled (in 3s), petiolate or sessile; blades deltate, lanceolate, or ovate, 2-41 × 0.5-24 cm, bases attenuate or truncate (distal connate-perfoliate), margins entire, dentate, or bidentate, apices acuminate to acute, faces scabrous to hispid. Phyllaries 25-37 in 2-3 series, outer appressed, apices acute to acuminate, abaxial faces scabrous or hispid. Ray florets 17-35; corollas yellow. Disc florets 85-150 (-200); corollas yellow. Cypselae 8-12 × 5-9 mm; pappi 0.5-1.5 mm.

Stems 1-2.5 m, square; lvs or their petiolar bases connate- perfoliate, the blade deltoid to ovate, coarsely toothed, to 3 נ1.5 dm; heads in an open infl, the disk 1.5-2.5 cm wide; invol 12-25 mm, its bracts elliptic or ovate, subequal or the outer longer, rays 1.5-4 cm; 2n=14. Woods and low ground; s. Ont. to N.D., s. to N.C., Miss., La., and Okla., and intr. into N. Engl. July-Sept. 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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