Senecio hydrophilus var. pacificus Greene

Perennials (biennials?), 40–100(–200) cm (caudices foreshortened, roots fleshy-fibrous). Herbage (often sea-green, usually glaucous) glabrous. Stems single or 2–4 loosely clustered. Leaves progressively reduced distally; ± petiolate; blades elliptic to oblanceolate, 5–20+ × (1–)2–10 cm, bases tapered, margins denticulate or entire (mid and distal leaves sessile, bractlike). Heads 20–40(–80+) in compound corymbiform arrays. Calyculi of 2–4+ bractlets (less than 2 mm). Phyllaries ± 8 or ± 13, 5–8 mm, tips frequently black. Ray florets (0) ca. 5; corolla laminae 3–5 mm. Cypselae glabrous. 2n = 40.

Flowering spring–early summer. Marshes, swampy places, standing water, alkaline sites; (0–)200–2500 m; B.C.; Calif., Colo., Idaho, Mont., Nev., Oreg., S.Dak., Utah, Wash., Wyo.