Mem. New York Bot. Gard. 1: 365. 1900.
Plants 10–50 cm. Leaves: basal 2–10, blade elliptic to lanceolate, 20–90 x 5–15 mm, 2(or 3)-pinnatifid, margins of adjacent lobes nonoverlapping to extensively overlapping distally, serrate, surfaces glabrous; cauline 2–8, blade triangular to lanceolate, 20–120 x 5–20 mm, 1- or 2-pinnatifid, margins of adjacent lobes nonoverlapping or extensively overlapping distally, serrate, surfaces glabrous or unevenly hispid to tomentose. Racemes simple, 1–2, exceeding basal leaves, each 10–40-flowered; bracts trullate to obtrullate or subulate to trullate, 10–25 x 2–5 mm, undivided or 1- or 2-auricled, sometimes 1-pinnatifid, proximal margins entire, distal entire or serrate, surfaces tomentose. Pedicels 1–3 mm. Flowers: calyx 8–12 mm, tomentose, lobes 5, narrowly triangular, 3–4 mm, apex entire, ciliate; corolla 20–26 mm, tube red or pink, 13–15 mm; galea red or pink, 7–11 mm, beakless, margins entire medially, 1-toothed distally, apex arching over abaxial lip; abaxial lip red or pink, 6–7.5 mm. 2n = 32.
Phenology: Flowering May–Aug.
Habitat: Rocky alpine tundras, meadows.
Elevation: 2100–3100 m.
Pedicularis cystopteridifolia occurs only in the Rocky Mountains of Montana and Wyoming. As the specific epithet implies, the leaves strongly resemble those of the fern Cystopteris fragilis. Although not sympatric, this species could easily be misidentified as P. sudetica subsp. scopulorum, which has flowers of a similar shape and color, and leaves that are also two-pinnatifid. The secondary leaf lobes of P. cystopteridifolia, however, are much larger, longer, more deeply incised, and more heavily toothed, making them appear more finely dissected than the linear to deltate secondary and smaller toothed lobes of P. sudetica. Many of the adjacent leaf lobes of P. cystopteridifolia also overlap, whereas the lobes of P. sudetica are more widely spaced and therefore not overlapping. The galea of P. cystopteridifolia is also more highly domed and broader, and the leaves are a paler shade of green in contrast to the dark green leaves of P. sudetica subsp. scopulorum.