hornwort is a good plant if given enough light and the proper nutrients to keep it healthy. It is a fairly easy plant to grow, and once it has the proper light etc it can tend to take over a tank fairly rapidly. I have to cut mine back every couple of weeks so that the plants in the lower substrate can get some light too. The plant should not be put directly in gravel as the bottom part will die off and then you will have a mess. You can either leave the plant to float or put a plant anchor around the base of the plant to hold it suspended upright in the tank. A couple of watts of light per gallon and a good fertilizer will ensure good plant growth for this species. HTH
Jim