Athyrium angustum, the northern lady fern, is a fern native to northeastern North America. It was long included in the superspecies Athyrium filix-femina, but is now largely recognized as a distinct species.
Athyrium angustum has a more southern counterpart â Athyrium asplenioides, the southern lady fern â that is very similar. The latter has a broader frond, especially at the base.