41. Packera plattensis (Nuttall) W. A. Weber & Á. Löve, Phytologia. 49: 48. 1981.
Senecio plattensis Nuttall, Trans. Amer. Philos. Soc., n. s. 7: 413. 1841; S. pseudotomentosus Mackenzie & Bush
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.