Hornwort (Ceratophyllum demersum) is another possibility. Check the leaf whorls positioning on the stem to see which plant yours matches.
When we grow stem plants rooted in the substrate, there are some maintenance issues to recognize. First, they are all fast growing plants, and that means the tips will grow toward the strongest light. As the lower stem portions receive less light, the leaves may die and fall off, leaving bare stems. Regular pruning will deal with this; uproot the stem(s) when this occurs, cut off the bare lower portions, and plant the cut end of the growing ends.