Perennials (possibly biennials), (10-)20-70 cm (caudices buttonlike, roots fleshy-fibrous). Herbage arachnose, loosely tomentose, or villous (hairs crisped, jointed), glabrescent. Stems single. Leaves progressively reduced distally; ± petiolate; blades elliptic, lanceolate, linear, oblanceolate, rounded-deltate, or suborbiculate, 6-25 × 1-6 cm, bases ± tapered or truncate to cordate, margins entire or ± dentate (distal leaves sessile, bractlike). Heads 6-20(-40+) in corymbiform arrays (peduncle of terminal head often shorter than others). Calyculi of 1-5+ linear to filiform bractlets (seldom more than 2 mm). Phyllaries usually ± 13 or ± 21, rarely ± 8, (4-)5-12(-15) mm, tips usually black, sometimes green. Ray florets usually ± 8 or ± 13, sometimes 0; corolla laminae 6-15(-20) mm (usually yellow, ochroleucous to white in one variety). Cypselae usually glabrous, sometimes hirtellous (mostly on angles). 2n = 40, 80.
The varieties of Senecio integerrimus are distinguished by morphology and geography.
Stout, single-stemmed, fibrous-rooted perennial 2.5-7 dm from a very short, erect caudex or crown, villous or hirsute with crisp loose hairs when young, commonly nearly glabrous by flowering time; lvs entire, denticulate, or sometimes irregularly dentate, the basal mostly oblanceolate or elliptic and short-petiolate, 8-25 cm (petiole included) נ1-5 cm; cauline lvs progressively reduced, becoming sessile; heads 5-25 in a rather congested infl, the terminal peduncle often shorter and thicker than the others; disk 8-17 mm wide; invol 5-10 mm, its bracts often minutely and irregularly black-tipped; rays 6-10 mm; achenes glabrous; 2n=40. Prairies and other open places; Sask., Minn., and Io., w. to B.C. and Calif. Apr.-June. Our plants are var. integerrimus.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.