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.
Alta., B.C., Man., Sask., Calif., Colo., Idaho, Iowa, Kans., Minn., Mont., N.Dak., N.Mex., Nebr., Nev., Oreg., S.Dak., Utah, Wash., Wyo.
Varieties 5 (5 in the flora).
The varieties of Senecio integerrimus are distinguished by morphology and geography.
|1||Basal leaves with distinct petioles, blades usually ovate to rounded-deltate, sometimes obovate to oblanceolate; ray corollas white or ochroleucous||Senecio integerrimus var. ochroleucus|
|1||Basal leaves with or without distinct petioles, blades elliptic, lanceolate, oblanceolate, rounded-deltate, sublinear, or suborbiculate; ray corollas yellow (or rays 0)||> 2|
|2||Herbage glabrous or glabrate at flowering (except in leaf axils and among heads); phyllaries linear-subulate, tips usually green, minutely (if at all) black||Senecio integerrimus var. integerrimus|
|2||Herbage usually arachnose, tomentose, or villous at flowering; phyllaries lanceolate to linear-subulate, tips black (if minutely so, then narrowly lanceolate and broader than subulate)||> 3|
|3||Basal and proximal leaves oblong or lanceolate to sublinear; heads 3–6(–16+); phyllaries 10–15+ mm||Senecio integerrimus var. scribneri|
|3||Basal and proximal leaves mostly elliptic to oblanceolate, sometimes elliptic or rounded-deltate to suborbiculate; heads usually 6–15(–30+; if fewer than 6, leaves lanceolate or broader); phyllaries 5–12 mm.||> 4|
|4||Plants copiously arachnose, tomentose, or villous at flowering; phyllaries linear-subulate, 8–12 mm, tips minutely, if at all, blackened||Senecio integerrimus var. major|
|4||Plants copiously to sparsely arachnose, tomentose, or villous at flowering; phyllaries mostly lanceolate (seldom as narrow as linear-subulate), 5–10 mm, tips black||Senecio integerrimus var. exaltatus|