Ceratophyllum

Ceratophyllum (commonly known as coontails) are a cosmopolitan genus of flowering plants commonly found in ponds, marshes, and quiet streams in tropical and in temperate regions. It is the only extant genus in the family Ceratophyllaceae, itself the only extant family in the order Ceratophyllales. They are often called "hornworts", although the second name is also used for Anthocerotophytes (which have a distinctive horn-like sporophyte). Coontails lack anything resembling a horn, so to avoid confusion, calling them "hornworts" is strongly discouraged.