Aerial shoots 5-30(-40) cm, from rhizomes, rhizomes horizontal. Basal leaves 0-1, ternate; petiole 5-8 cm; terminal leaflet sessile to petiolulate, ovate to oblanceolate, (1-)1.5-3(-4) × (0.4-)0.7-1.5(-2) cm, base narrowly cuneate, margins serrate to crenate on distal 1/2-2/3, apex acuminate to narrowly acute, rarely obtuse, surfaces glabrous, rarely puberulous; lateral leaflets unlobed or occasionally nearly lobed. Inflorescences 1-flowered; peduncle distally puberulous or nearly glabrous throughout; involucral bracts 3, 1-tiered, ternate, ±similar to basal leaves, bases distinct; terminal leaflet sessile to petiolulate, ovate to oblanceolate, (1-)1.5-3(-4) × (0.4-)0.7-1.5(-2) cm, bases narrowly cuneate, margins serrate to crenate on distal 1/2-2/3, apex acuminate to narrowly acute, rarely obtuse, surfaces glabrous, rarely puberulous; lateral leaflets unlobed or occasionally nearly lobed. Flowers: sepals 5(-7), white, pink, or sometimes blue-tinged, oblong, rarely narrowly ovate, 3.5-8(-10) × 1.5-3(-3.5) mm, glabrous; stamens 10-30(-35). Heads of achenes nearly spheric; pedicel 1-3(-4) cm in fruit. Achenes: body elliptic, flat, 3-4 × 1-1.5 mm, not winged, white-puberulous; beak subulate, sometimes slightly curved, ca. 0.5 mm, glabrous. 2 n =16.

Flowering spring-summer (Mar-Jul). Shaded woods, subalpine ridges; 200-1900 m; B.C.; Calif., Oreg., Wash.

Anemone lyallii may occasionally intergrade with A . oregana west of the Cascades in northern Oregon (C. L. Hitchcock et al. 1955-1969, vol. 2). The area of probable intergradation should be extended to the southern limits of both species where they are sympatric.