It has a superficial resemblance to Swamp Fern Blechnum serrulatum . The once-divided fronds are dark green. The pinnae are lightly serrated along the edge. The pinna at the tip of the frond is usually longer than the other pinnae, and its base is clearly unevenly divided. Plants growing on open rock are usually much smaller than plants growing in rich soil.
Spores form lines along the edges of each pinna.
In Swamp Fern, the spores form lines along the midrib of each pinna.