Funny story. This is the inside a little cold frame/box I built about 12 years ago to protect small seedlings and plants. Over the years I've tried various holly ferns and have had the hardest time getting them established. I definitely DID NOT plant one in this frame, but it's quite possible I had one in there, in a pot, before it was planted elsewhere. Could a spore a few years ago have sown itself? (another more conventional looking fern has also found a home here)