Plants 25 -50(-100) cm. Basal leaves: blades (green, shining) lance-elliptic or oblong-lanceolate to lanceolate, 15-30(-40+) cm, margins usually entire, sometimes denticulate or dentate, not ciliate, faces glabrous (gland-dotted, vernicose); cauline leaves similar, smaller distally (distalmost sessile, usually ± clasping). Heads usually 2-8 in ± corymbiform to racemiform arrays, sometimes borne singly. Involucres hemispheric to turbinate, 15-30 mm diam. Phyllaries 18-36+, subequal or unequal, herbaceous (at least outer), margins not ciliate, faces glabrous; outer 18-32 mm (surpassing inner). Ray florets 8-21(-25); laminae 25-60 mm. Cypselae 8-9 mm, glabrous. 2n = 38.
Flowering May-Jul. Wet to dry, open sites, meadows, sagebrush scrub, yellow-pine forests; 400-3000 m; Colo., Idaho, Mont., Nev., Oreg., Utah, Wash., Wyo.
Wyethia amplexicaulis introgressively hybridizes with W. arizonica (producing plants called W. ×magna A. Nelson ex W. A. Weber) across a broad area of central and southern Colorado. Habit of the hybrid is typical of W. amplexicaulis; the indument resembles that of W. arizonica in varying degrees. Occasionally, W. amplexicaulis hybridizes with but does not introgress with W. helianthoides.