Need help identifying fern through description
I went out to eat at a restaurant a few weeks ago and they had the most beautiful ferns in their garden I ever saw. The ferns were very tall (about 4') and very upright. In the center of each frond were smaller fronds (leaves) that were black. The owner told me that they grow to normal size and change to green later at end of May/June (right about now) and that later in the season fiddleheads appear at the top of the ferns. This seems particularly strange to me because I always thought that fiddleheads only appear in early spring when the ferns are pushing up from the ground. She said the plants have been there longer than she has (50 years) and is not sure of the variety but thinks it might be called a Fiddlehead fern. So, I did a google image search for fiddlehead fern and nothing even closely resembled it. All I saw where fiddleheads and lots of recipes. LOL I then searched and came up with Royal Fern, Cinamon, and Ostrich and none of them looked like it. The only one that came close was Interrupted Fern but it didn't appear to grow as tall or as upright as the ferns at the restaurant and appears scraggly in comparison. Also, in all the descriptions about Interrupted Fern none mentioned anything about fiddleheads appearing at the top at the end of the summer.Maybe she's wrong on that because I never heard of anything like this before but she assured me that if I returned at the end of the summer I would see the fiddleheads for myself. Anyway, if anyone has any idea what this fern is please let me know. Thanks. Oh, and I am trying to go back to the restaurant as soon as I can but it's some distance away from where I live.