I got a tiny bit of this months ago as a hanger on in a plant bag.
It has grown out to a decent sized clump now. Odd moss - the older stems seem to go brown for me, and it doesn't like to attach to wood. It is slowly recovering, as you can see from the bits still in it, from a thread algae attack - tank is doing much better, this stuff still has some in it. I don't want to trash it, as I've never seen moss like it before I got it or since.
Is this Willow moss, or something else? I put the penny in for size reference. This stuff has large fronds, much bigger than my christmas moss or fissidens.