Senecio hydrophilus

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.