Biennials or perennials, 20-60+ cm; rhizomatous and/or fibrous-rooted (bases erect to suberect), sometimes stoloniferous (mostly eastern populations).
Stems 1 or 2-3, clustered, floccose-tomentose proximally and in leaf axils, otherwise sparsely tomentose or glabrescent.
Basal leaves (and proximal cauline) petiolate; blades narrowly elliptic to elliptic-ovate or oblanceolate to suborbiculate or sublyrate, 20-70+ × 10-30+ mm, bases tapering to rounded or abruptly contracted, margins subentire to crenate, serrate-dentate, or pinnately lobed (abaxial faces floccose-tomentose, especially along midribs, ± glabrescent).
Cauline leaves gradually reduced (petiolate, sublyrate or pinnatisect, abaxial faces sparsely hairy; distals sessile, subentire to irregularly dissected).
Heads 6-20+ in open or congested, corymbiform arrays.
Peduncles conspicuously bracteate, sparsely to densely tomentose.
Calyculi inconspicuous.
Phyllaries 13 or 21, green (tips sometimes cyanic), 5-6+ mm, densely tomentose proximally, glabrescent distally.
Ray florets 8-10; corolla laminae 9-10 mm.
Disc florets 60-70+; corolla tubes 2.5-3.5 mm, limbs 3.5-4.5 mm.
Cypselae 1.5-2.5 mm, usually hirtellous, sometimes glabrous;
pappi 6.5-7.5 mm.
2n = 46, 92. Flowering mid Apr-early Jun(-mid Jul, north). Prairies, meadows, open wooded areas, along highways, railroads, around mining and construction areas, usually on limestone; 50-1800 m; Ont., Sask.; Ark., Colo., Ga., Ill., Ind., Iowa, Kans., La., Mich., Minn., Miss., Mo., Mont., Nebr., N.Mex., N.Dak., Ohio, Okla., Pa., S.Dak., Tenn., Va., Wis., Wyo.
Packera plattensis is abundant, widespread, and almost weedy. Putative hybrids with other species are known. Plants in mesic, remnant prairies in the east are sometimes stoloniferous.
