Spreading woodfern is a medium-to-large sized fern that grows in lowland forests up through subalpine meadows to isolated protected alpine sites, preferring humid, shaded locales. This species is much more common south of the Alaska Range than to the north, likely because the maritime, humid climate there suits this species better. Plants grow from a stout, ascending rhizome, the leaves in clusters. Fronds are 20-70 cm tall and twice pinnately divided, the pinnae themselves pinnatifid. The lowest pinnae are more or less the same length as the next highest pair, but broader than all other pinnae. These pinnae are also asymmetrical: the leaflets on the lower half are conspicuously longer the upper leaflets. The frond gradually narrows to a point. Fronds are brown-scaly when in bud, retaining the scales on much of the stem. On the backs of the leaves there is a white indusium, horse-shoe shaped and circa 1 mm wide. This serves to cover the brown sori. Spreading woodfern is dissimilar in outline to the narrow Dryopteris fragrans and the horseshoe-shaped indusium separates it from any other genus of fern that occurs in Denali.
Dryopteris expansa is a perennial with late-deciduous leaves. Spore production occurs in mid-summer.
Spreading woodfern bladderfern is spore-producing, growing in two stages like all ferns. The plants we think of as ferns produce spores. Spores germinate into haploid gametophytes, which can be fertilized to become new, diploid ferns. It has a mixed mating system; gametophytes can be both out-crossing and self-fertilizing. The level of outcrossing may be related to densities of plants in a population (Soltis and Soltis 1987).
The fiddleheads are edible, collected in early spring before they unfurl. The rhizomes are also edible and were eaten by Natives as a survival food (Turner et al. 1992).
Dryopteris expansa is a circumpolar boreal-montane species (with wide gaps). In North America, this species occurs across the continent, with gaps in dry areas in the middle of the continent where it does not occur (e.g., Saskatchewan, Manitoba, and the Dakotas). In Alaska, this species occurs in isolated localities in the Brooks Range becoming much more common in boreal mountains further south, and occurs most abundantly on the south side of the Alaska Range and in southeast Alaska. Dryopteris expansa occurs in scattered localities north of the Alaska Range crest in Denali, but is abundant on the south side from the lowlands into the lower alpine zone of the park.
This species is found on both low and high elevations, from 67 to 1472 m. It also tolerates a wide range of slopes. Spreading woodfern is slightly more common on south-facing slopes than northern-facing slopes.