This looks like Sensitive Fern (Onoclea sensibilis), which is a native perennial that probably self-seeded (ferns have spores and not seeds, but the principle of how they can spread that way is the same) on its own into that location. They get their name because of the rapid dieback the fronds have once frosty weather arrives in autumn ("sensitive" to the cold, even though they are winter-hardy; they're not an evergreen species; few local ferns are).

Miri