If possible, place the plnat high enough up so the stems can break the surface of the water. It will live with roots submerged, but needs to have most of the leaves in the air to really survive for more than a few months. Most terrestrial plants are capable of 'shutting down'--they live on their reserves, waiting for the water to recede. Once the reserves are depelted, the plant dies off. But, if you give it access to air, they'll typically do decently enough. I had to remove mine when some fish decided it was tasty, but it was in the tank for about 9 months.
