This is a subspecies of the circumpolarD. integrifolia complex, which occurs in woods, meadows, and shrublands from the boreal zone into the lower alpine, most common in river terraces environments north of the Alaska Range crest in Denali. Forest mountain avens is a low-growing dwarf shrub with long, thin leathery leaves and broad white flowers. Its morphology is similar to the more common Dryas integrifolia. The plants form dense mats low to the ground, with persistent dead leaves attached to the woody stems. The leaves are thick, dark green on top and white-hairy below, the margins only barely inrolled (unlike D. integrifolia ssp. integrifolia). Leaves of this subspecies are particularly long, on long petioles, and have rounded tips. This is in contrast to the more pointed tips of D. integrifolia ssp. integrifolia. The flowers grow on slender, leafless stalks held high above the leaves. Flowers have eight to ten white petals, hairy sepals and many stamens and pistils. The fruiting head has many small achenes, which are attached to long, feathery styles, which catch the wind to transport the seeds. Leaves are flat and smooth, in contrast to other subspecies of D. integrifolia, with only narrowly revolute margins, if margins in-rolled at all.
Forest mountain avens is a perennial species with semi-evergreen leaves. It flowers in early to mid-summer.
This species is monoecious with bisexual flowers. Dryas flowers are insect-pollinated. D. integrifolia subsp. integrifolia is self-compatible and out-crossing, but no studies have been done on the reproductive biology of D. integrifolia subsp. sylvatica. The fruiting head has many small achenes, which are attached to long, feathery styles, which catch the wind to transport the seeds.
Dryas integrifolia subsp. sylvatica occurs only in Alaska, the Yukon and the northwestern Northwest Territories, extending southward into northern British Columbia. This taxon occurs in widely scattered locations across Alaska, usually in more boreal sites than the other subspecies of D. integrifolia which are alpine plants. In Denali, this taxon occurs north of the Alaska Range crest, primarily in the northeastern quadrant of the park.