They have a moderate growth rate, spreading from stout, densely scaly, short rhizomes. They are deciduous, collapsing with the first hard frosts. The ones I've found in the woods tend to be smaller than the clump I moved to the garden. They prefer a fertile, woodland type, moist soil and tend to flop when the soil under the trees gets too dry in summer. For years, I had not identified this fern.
Research indicates that it has to be a lady fern.
I've also learned that my garden clump is probably in too dry and shady a location to make it really happy. They prefer light to part shade but will take full sun in very moist soil. They usually do best in a slightly acid soil but are adaptable to more alkaline sites. The genus is a large one with species found throughout most of the temperate world. It includes the very lovely and popular Japanese painted fern, Athyrium niponicum 'Pictum' .