2. Trollius albiflorus (A. Gray) Rydberg, Mem. New York Bot. Gard. 1: 152. 1900.
Trollius laxus Salisbury var. albiflorus A.Gray, Amer. J. Sci. Arts, ser. 2, 33: 241. 1862
Stems 0.7-5.5 dm (to 8dm in fruit), base with few petioles persistent from previous year. Leaves: basal leaves with petioles 4-25 cm, some leaves reduced to sessile, ovate membranous scales; cauline leaves 1-3(-5), with broad, clasping, membranous sheaths. Flowers 2.5-5 cm diam.; sepals 5-9, spreading, white when fresh (pale yellow to greenish white before anthesis), ovate to obovate or nearly orbiculate, 10-20 mm; petals 15-25, yellow, 1/2-2/3 length of stamens when pollen shed, 3-6 mm. Follicles usually 11-14, 8-16 mm including beak; beak often somewhat recurved, sometimes straight. 2 n =16.
Flowering summer. Open, wet places, ±acidic, montane to alpine; 1200-3800 m; Alta., B.C.; Colo., Idaho, Mont., Utah, Wash., Wyo.
The diploid Trollius albiflorus is isolated from the tetraploid T . laxus ecologically, geographically, and reproductively, although it often has been treated as a variety of the latter.
Identities of specimens of Trollius albiflorus and the superficially similar Anemone narcissiflora subsp. zephyra in Colorado and Wyoming are sometimes confused. Close examination reveals a number of differences. The anemone has sepals yellow (not white), leaf blades and flowering stems pilose to villous (not glabrous), achenes (not follicles), and leaflike bracts subtending the pedicels and whorled (leaves alternate in Trollius ).