Which among the following is a rootless plant?

Step-by-step solution

All the given options are hydrophytes in nature which grow in extremely wet or watery conditions. But among them only in Ceratophyllum roots are completely absent even in embryonic stage. They remain under water completely. Nymphaea is a rooted hydrophyte with floating leaves, Vallisneria is rooted submerged hydrophyte and Sagittaria is rooted emergent hydrophyte.