I am guessing that you are talking about Hygrophila polysperma, but you could also be talking about salicifolia, stricta or difformis. They can all develop arial type roots when grown submersed and can basically be ignored. Most hygrophilas will grow a plant from a floating leaf and a way to propagate polysperma is to get it rooted then weight the stem down so it is laying flat and a plant will grow from each leaf node.