Annuals or biennials (perhaps rarely perennials), 20-100 cm (loosely arachnose or villous, hairs white, light yellowish, or reddish brown, indument fugitive in some populations; caudices fibrous-rooted). Stems single. Leaves basal and cauline (basal and proximal sometimes withering before flowering, mid-stem leaves prominent at flowering); petioles weakly defined; blades oblanceolate to linear-oblanceolate or spatulate, 5-15 × 0.5-3(-5) cm, margins subentire to coarsely dentate or subpinnatifid (distal leaves bractlike). Heads (4-)6-20(-40+), in loose to crowded, corymbiform arrays. Involucres ± abruptly contracted to peduncles. Phyllaries usually 21, green or yellowish green (tips sometimes pinkish), 4-10 mm. Ray florets (13-)21+; corolla laminae 5-9+ mm (sometimes incompletely opened, appearing tubular). Disc florets 30-50; corollas yellow. Cypselae glabrous; pappi white or dirty white. 2n = 48. Flowering May-Sep. Wet soils, shorelines, pond margins, brackish habitats; 0-1000 m; Alta., B.C., Man., Nfld. and Labr. (Labr.), N.W.T., Nunavut, Ont., Que., Sask., Yukon; Alaska, Iowa, Mich., Minn., N.Dak., S.Dak., Wis.; Eurasia. Tephroseris palustris varies greatly in stature and in distribution and persistence of tomentum. The variations have been used to distinguish infraspecific taxa or two species; contemporary thought is that the complex is best treated as a single, polymorphic species.
Coarse, single-stemmed, fibrous-rooted annual or biennial 1.5-15 dm; pubescence spreading, crisp-villous, commonly persisting in large part until flowering time or beyond, especially in the infl; lvs entire or coarsely toothed, scarcely pinnatifid, rather equably distributed, 3-20 נ0.5-4.5 cm, the lower petiolate and often soon deciduous, the upper becoming sessile and ±clasping; heads several or numerous in an often congested infl, the disk 7-14 mm wide, or larger in fr; invol 7-10 mm, its bracts ca 21, very thin and generally pale, commonly with darker base; rays pale yellow, 4-9 mm; pappus accrescent, very fine and copious; achenes glabrous; 2n=48. Swamps and edges of ponds; circumpolar, s. in our range to Minn. and extreme n. Io. June-Aug. (S. palustris, a preoccupied name)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.