Perennials, (10-)20-35(-50) cm (rhizomes suberect to creeping). Herbage loosely, often unevenly, floccose-tomentose, glabrescent. Stems single or clustered. Leaves reduced distally; petiolate; blades narrowly obovate to oblanceolate, (4-)8-18(-25) cm, bases tapered, margins subentire to dentate (denticles callous; mid and distal leaves bractlike, clasping). Heads (2-)7-12(-20+) in corymbiform arrays. Calyculi of 2-5 linear bractlets (1-2 mm). Phyllaries (± 8) ± 13 (± 21), 4-7 mm, tips black. Ray florets (± 5) ± 8 (± 13); corolla laminae 8-10(-15) mm. Cypselae glabrous. 2n = 40, 80.

Flowering summer. Moist meadows, gravelly streambeds, open woods in alpine or boreal sites; 200-2500 m; Alta., B.C., N.W.T., Yukon; Alaska, Mont., Wash., Wyo.

Senecio lugens varies greatly in robustness across its range. It is scattered widely in the Rocky Mountain uplift and adjacent regions from northern Wyoming to Alaska; it is disjunct in the Olympic Peninsula, Washington. Superficially similar to S. integerrimus, S. lugens has well-developed, coarse, spreading rootstocks with branching roots; S. integerrimus arises from foreshortened, buttonlike caudices with abundant unbranched, fleshy-fibrous roots.