5.
Silphium perfoliatum
Linnaeus, Syst. Nat. ed. 10. 2: 1232. 1759.
Cup plant
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.
Varieties 2 (2 in flora): e North America.
