Plants in your fish tank are an interesting thing. Plants come in several groups. There are those that Like being fully submerged. There are some that need to have part of it outside the water. You also have plants that need to be in very wet soil but keeping the leaves mostly dry. Then there are those who like to be planted in regular soil and not get very wet at all to those that barely want any water at all near them most of the time. In your tank this narrows down to those that like being submerged and those that have part hanging out of the water. This can be floating plants or those that have mostly roots below the water surface and leaves above.

You need to be careful though because some plants ARE poisonous to fish even if they dont eat them sometimes. Other plants just do not like being exposed to water all the time and will then start to rot and pollute the water. You will find most house plants are not compatible with aquariums.

For a good source of information on aquatic plants you should probably start with Tropica which operates out of Denmark. They supply a major part of the world with about 150 different species of plants. Also The Krib's Plant Section is an excellent resource as well.