1a. Petasites frigidus (Linnaeus) Fries var. frigidus
Petasites alaskanus Rydberg; P. corymbosus (R. Brown) Rydberg; P. frigidus var. hyperboreoides Hultén; P. frigidus var. nivalis (Greene) Cronquist; P. gracilis Britton; P. hyperboreus Rydberg; P. nivalis Greene; P. nivalis subsp. hyperboreus (Rydberg) J. Toman
Basal leaves: blades palmately nerved, sagittate, deltate, or reniform to cordate, 2–25 × 2–27 cm, margins lobed (primary lobes 0–14, entire or dentate, secondary lobes 0–25, entire or irregularly toothed, lobed, or deeply parted, in extreme forms lobes with at least 2 lateral triangular teeth, lobes often overlapping, sinuses oblong and closed) or not lobed (dentate, teeth to 22 per side), abaxial faces floccose to woolly, adaxial faces mostly glabrous or sparsely tomentulose. Staminate heads 2–20; ray florets 1–13, corolla laminae 1.6–12 mm; disc floret style branches 0.05–2 mm, papillate or hairy. Pistillate heads 5–19; ray florets 30–109, corolla laminae 0.8–4.8 mm; disc florets: corolla lobes 0.4–4.4 mm, style branches 0–1.2 mm, papillate or hairy. Pappi (pistillate) to 15 mm. 2n = ca. 60, 90.
Flowering early spring. Arctic tundra, moist alpine-subalpine slopes, streams, marshes, edges of moist forests, gravelly or sandy roadsides; 10–2300 m; Alta., B.C., N.W.T., Nunavut, Sask., Yukon; Alaska, Oreg., Wash.; n Eurasia.