I recently bought some water sprite (ceratopteris thalictroides) from you. Is this the variety that can grow on the top of the tank without being planted?
The water sprite plant can exist in two forms: both planted into a substrate and free floating. So the answer to your question is yes, this plant will grow if left floating on the top of the surface. With time young plantlets will develop on the leaves of the adult plant. After some time they will detach from the mother plant and will assume their floating form unless planted.