Mountain bladderfern is a medium-sized fern that occurs in meadows, shrub thickets, rocky outcrops, and woodlands, usually in the mountainous areas of the park. Cystopteris montana grows from a creeping black rhizome, with emerging fronds evenly spaced from each other. The rachis, or stem, of the frond is longer than the blade, the whole leaf up to 40 cm tall. Fronds are thrice pinnate-pinnatifid, the smallest leaflets pinnately lobed and toothed on the tips. The blade is broad, roughly triangular in outline, considerably wider than it is long. The lowest pair of pinnae is much longer than any other set. The stipe is darker at the base, with a few scales. All leaves are fertile, with a white indusium covering the sporangia. When revealed, the sori are clusters of dark brown spore-sacs. The closely related C. fragilis is twice as long as it is wide. The species could be also be confused with Gymnocarpium dryopteris, but leaves of that species do not have indusia.
Cystopteris montana is perennial and sheds its leaves each season. Spore production occurs in mid-summer.
Mountain bladderfern is spore-producing, growing in two stages like all ferns. The plants we think of as ferns produce spores. Spores germinate into tiny haploid gametophytes, which can be fertilized to become new, diploid ferns. The reproductive biology of C. montana has not been studied.
Cystopteris montana has a circumpolar range with large gaps. This species occurs across boreal North America, with disjunct southern stations in Colorado's Rocky Mountains. Mountain bladderfern occurs sporadically in central and southern mountains of Alaska (Ogilvie and White Mountains, Alaska Range, Wrangell, Kenai, Chugach, and St. Elias Mountain ranges) westward to the Seward Peninsula and north to isolated stations in the Brooks Range. In Denali, mountain bladderfern is known from scattered localities in the mountains on both sides of the Alaska Range crest, with occasional localities in the lowlands.
This is a species of the subalpine; its frequency peaks at 700-900 meters, with an average elevation of 854 m. Mountain bladderfern is found on all degrees of slopes, averaging 17 degrees incline. There have been slightly more specimens found on southern slopes (but the sample size is not especially large). Though this species is not uncommon, it is never abundant.