Hornwort is a good plant for aquariums with plant eating fish, since the hard leaves do not taste so good!
A rootless plant, Hornwort can be kept floating at the top of the aquarium or buried in the gravel to suit your taste. If you bury Hornwort in the substrate, the Hornwort stems are held in the gravel by root-like organs called rhizoids. The stems will branch off to form nice thickets for fish and especially fry to retreat into. Be careful with it however, because it breaks easily and many of the pieces can become their own plants. Hornwort is an easy plant to care for since
Hornwort can be kept in many aquarium environments, such as coldwater aquariums and tropical aquariums. It is a great aquarium plant for all levels of experienced aquarists. It is also readily available at fish stores or online.
For more Information on keeping a planted aquarium see:
About Planted Aquariums, Adding Aquatic Plants For a Healthy Aquarium