Some friend once gave me (in Germany) spores of a fern on the US East Coast, which, once I grew fern out of those spores, turned out to be a Christmas fern. But there was another fern growing in there too. So it could either be from the US East Coast or here in Germany have found its way randomly into the pot.
I looked at some fern galleries but didn't find it there.
We're going to need pictures of the entire plant, and additional information like does it die back to the ground in the winter, is it a running or a clumping fern...
We have A lot of native ferns, and many of them have similar foliage.
As it grew from spores with another fern, the one from the photos was closely intertwined with another. My partner tried to help it by sorting the two fern apart and giving them each their own pot, with the result that the one of the photo seems to have very quickly died. As such, I can't make new photos, unless those of a dead fern help. I found some more photos on my smartphone, but I guess they won't provide the necessary information. Thank you regardless.