Plants 15-80 cm; taproots slender to thickened, tuberous. Stems 1(-10), erect or ascending, green to purple, usually simple, glabrous or glabrate proximally, tomentulose distally. Leaves: proximal present at flowering; petioles winged (2-6 cm); blades triangular to irregularly elliptic, 3-25 × 1-7 cm, thin or slightly coriaceous, bases abruptly constricted, truncate to slightly hastate, margins irregularly dentate or coarsely serrate, apices acute to acuminate, faces glabrate; distal sessile, ovate to lanceolate, reduced. Heads (10-17) in broad, corymbiform arrays, lateral branches often elongate and overtopping main stems. Involucres narrowly campanulate, 10-13 × 5-6 mm. Calyculi of 2-3, dark green, lanceolate or subulate bractlets 1-3 mm, glabrous or finely tomentulose. Phyllaries 8, green to dark green, lanceolate, 8-11 mm, margins scarious, apices acute, finely tomentulose. Florets 7-16; corollas white to purplish, 9-16 mm. Cypselae brown to light tan, subcylindric, 4-7 mm, weakly 7-10-ribbed; pappi pale yellow to dull white, 8-10 mm. 2n = 16.

Flowering Jun-Sep. Stream banks, mountain springs, seeps, cliffs near shore, moist shady places; 0-1500 m; Alta., B.C.; Alaska, Idaho, Mont., Oreg., Wash.

Prenanthes alata is recognized by its relatively small size, elongate and winged petioles, triangular-hastate leaf blades, heads in broad corymbiform arrays, and dark green, finely tomentulose phyllaries.