Deer fern fronds are dimorphic. Sterile leaves are evergreen and are spreading or appressed to the ground.
Fertile leaves are fewer in number, deciduous, and much longer than the sterile leaves.
Sporangia are confluent and parallel to the midrib. Deer fern reproduces from spores and by sprouting from rhizomes. It is an indicator of hypermaritime to maritime subalpine boreal and summer-wet cool mesothermal climates. Disturbance in these cool, wet forests is generally from windthrow or logging. Along the west coast of Vancouver Island, British Columbia, deer fern may be present in young seral stands in floodplain succession.