Java Fern.
I have a single Java fern and to begin with it was both big and pretty. Unfortunately is has shrunk quite a bit, but it is still pretty.
It does not have to be planted in substrate, it grows fine on a rock, a root or simply in a pot that you can move around. That's the way mine is planted. The good part about plants that like to grow in pots or on other movable substrates, is that you can easily throw a plant in a breeding tank or remove a plant if it get's in the way when capturing fish.
In time it will grow small off shoots on the leaves and they can turn into individual plants. Sometimes the off shoots also grows on torn off leaves floating in the surface.
