Summa Veg. Scand., 182. 1845.
Plants 10–60(–120) cm. Rhizomes much branched, creeping, often forming long-lived, spreading clones. Basal leaves: blades mostly reniform, orbiculate-cordate, cordate, ovate, triangular, or sagittate, margins subentire to coarsely dentate to wavy, or shallowly to deeply pinnipalmately or palmately lobed, lobes obtuse to acute, often again lobed or toothed, abaxial faces densely white-tomentose to lanate, adaxial faces densely lanate or floccose, glabrescent, or glabrous. Staminate heads 2–53 (ray florets: 0 or 1–70, styliferous and sterile, corolla laminae 1.1–12 mm; disc florets 11–78, functionally staminate; style branches 0–2.3 mm, papillate or hairy). Pistillate heads 5–60 (ray florets 30–139, pistillate and fertile, corolla laminae 0.6–6.3 mm; disc florets 1–12, functionally staminate, style branches 0–2.3 mm, papillate or hairy). Phyllaries: staminate 3.6–12.8 × 1–4.4 mm, pistillate 1–9.5 × 0.7–3.3 mm, margins entire or serrate. Cypselae 1.7–3.5 mm; pappi (longest, pistillate heads) 7–17.3 mm.
Alta., B.C., Man., N.B., N.S., N.W.T., Nfld. and Labr., Nunavut, Ont., P.E.I., Que., Sask., Yukon, Alaska, Calif., Colo., Conn., Idaho, Maine, Mass., Mich., Minn., Mont., N.Dak., N.H., N.Y., Oreg., R.I., S.Dak., Vt., Wash., Wis., Wyo., Eurasia.
Varieties 4 (4 in the flora).
|1||Basal leaves: blades sagittate or triangular to oblong (bases usually cordate, rarely hastate), margins not lobed, subentire or sinuate-dentate to callous-denticulate (teeth 11–45 per side), abaxial faces densely woolly to villous, adaxial faces tomentose and glabrescent or glabrous; staminate heads 8–35, ray florets 4–19, corolla laminae 1.1–7.7 mm, disc floret style branches 0.5–2.3 mm, hairy; pistillate heads 6–34, ray florets 31–139, corolla laminae 0.6–5.4 mm, disc florets: corolla lobes 0.4–1.8 mm, style branches hairy; pappi (pistillate) to 17.3 mm||Petasites frigidus var. sagittatus|
|1||Basal leaves: blades sagittate, deltate, cordate, reniform, or orbiculate, margins lobed (and both faces glabrous or tomentulose to woolly) or dentate (teeth to 22 per side and abaxial faces floccose, adaxial faces mostly glabrous or sparsely tomentose); staminate heads 2–32, ray florets 1–70, corolla laminae 1.6–12 mm, disc floret style branches 0.01–2 mm, papillate or hairy; pistillate heads 5–42, ray (and/or pistillate) florets 30–125, corolla laminae 0 or 0.1–6.3 mm, disc florets: corolla lobes 0.4–4.4 mm, style branches papillate or hairy; pappi (pistillate) to 15 mm||> 2|
|2||Basal leaves: blades orbiculate or cordate to reniform, margins lobed (primary lobes 5–11, sinuses sometimes almost to center, secondary lobes 0–13), margins entire or dentate (teeth to 52 per side); staminate heads 4–32, ray florets 5–70, corolla laminae 0.1–6.3 mm, disc floret style branches 0–1.7 mm; pistillate heads 8–42, ray florets 51–125, corolla laminae 0–6.3 mm, disc corolla lobes 0.5–2.9 mm; pappi (pistillate) to 11.8 mm||Petasites frigidus var. palmatus|
|2||Basal leaves: blades sagittate, deltate, reniform, or cordate, margins lobed (primary lobes to 14, secondary lobes 0–25, and teeth to 44 per side) or dentate (teeth to 22 per side); staminate heads 2–32, ray florets 1–27, corolla laminae 1.6–12 mm, disc floret style branches 0.05–2 mm; pistillate heads 5–34, ray florets 30–109, corolla laminae 0.8–4.8 mm, disc corolla lobes 0.4–4.4 mm; pappi (pistillate) to 15 mm||> 3|
|3||Basal leaves: blades deltate or cordate to reniform (bases usually convex-curved), margins lobed (primary lobes 4–14, triangular, secondary lobes 0–11, entire or dentate, teeth to 44); staminate heads 3–32, ray florets 2–27, corolla laminae 2.1–7.8 mm, disc floret style branches 0.4–1.4 mm; pistillate heads 9–34, ray florets 48–89, corolla laminae 0.8–2.5 mm, disc corolla lobes 0.8–2 mm||Petasites frigidus var. ×vitifolius|
|3||Basal leaves: blades sagittate, deltate, or reniform to cordate, margins lobed (primary lobes to 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); staminate heads 2–20, ray florets 1–13, corolla laminae 1.6–12 mm, disc floret style branches 0.05–2 mm; pistillate heads 5–19, ray florets 30–109, corolla laminae 0.8–4.8 mm, disc corolla lobes 0.4–4.4 mm||Petasites frigidus var. frigidus|