Your Plant
Hello rolling...
In my non professional plant ID opinion, it looks very much like a small fern, possibly Java fern. If you want the scientific name, it's Microsorum pteropus.
Try attaching it to a small piece of driftwood with some dark sewing thread and let the wood float or you can weigh the piece down with some rocks. I think Java fern grows better attached to driftwood than lava rock, but that's me. Attached is a pic of an experimental tank I use to grow plants using different liquid ferts. I have some Java fern floating in this 45 G.
B