Silphium terebinthinaceum Jacq.
Family: Asteraceae
prairie-dock
[Silphium terebinthinaceum var. luciae-brauniae Steyerm.,  more]
Silphium terebinthinaceum image
Paul Rothrock  
Plants scapiform, (40-)100-250+ cm; taprooted. Stems terete, glabrous. Leaves: basal persistent, petiolate; cauline alternate, petiolate or sessile; blades cordate, deltate, lanceolate, ovate, or sagittate, 3-40 × 1-40 cm, sometimes (proximal) pinnately lobed, bases attenuate, cordate, hastate, round, or truncate, ultimate margins coarsely toothed or entire, apices acuminate, acute, or obtuse, faces glabrous or scabrous. Phyllaries 23-33 in 2-3 series, outer appressed, apices obtuse to acute, abaxial faces glabrous. Ray florets 17-29; corollas yellow. Disc florets 120-140; corollas yellow. Cypselae 7-13 × 4-10 mm; pappi 0-1 mm.
Taprooted; stem 0.7-3 m, essentially glabrous, nearly naked, its lvs, except those near the base, few and reduced to mere large bracts; principal lvs large, long-petiolate, the blade narrowly to broadly ovate, oblong, or elliptic, usually cordate (seldom only subtruncate) at the base, 1-5 נ0.7-3 dm, usually sharply toothed, glabrous or scabrous, sometimes hirsute on the midrib beneath; heads several or rather numerous in an open-corymbiform infl, relatively large, with ca 13 to ca 21 rays 2-3 cm, the disk 1.5-3.5 cm wide; invol 13-25 mm, its bracts essentially glabrous, strongly imbricate, the outer broadly elliptic, the inner elongate, more oblong, loose and broad- tipped; 2n=14. Prairies; s. Ont. and O. to Minn., s. to Ga. and Miss. July-Sept. (S. rumicifolium)

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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