tiny what

Two months ago I got an additional handful of  salvinia minima from someone in fish club, and there were tiny bits of another plant mixed in. Seemed too small to bother picking them out, and I assumed they would die from the cold. They didn't. I was cleaning out a few browned salvinia pieces yesterday and sorted out all the tiny unknown plant. It has very small round leaves. Looks like the dwarf rotala rotundifolia I once bought in a tissue packet? but I think this is even smaller.

Regardless, since it was still alive I decided to see how it would do planted. Tucked the tiny stems in, they're even dwarfed by the substrate particles.