Is it a fern . . . ?

. . .  yes, of course it's a fern! It may not look like your average common or garden fern, but it's the very special Dryopteris sieboldii, from Japan, China and Taiwan.

It's never been very successful up here on the west coast and struggles to survive. It comes into frond late and is easily battered by the wind. I suspect that it really likes a lot of warmth and shelter and would probably appreciate a conservatory or a shady window indoors given the option.

Further south it does a lot better and when grown well is a very distinctive and beautiful fern.