Ceratophyllales

Ceratophyllaceae is a cosmopolitan family of flowering plants including one living genus commonly found in ponds, marshes, and quiet streams in tropical and in temperate regions. It is the only extant family in the order Ceratophyllales. Species are commonly called coontails or hornworts, although hornwort is also used for unrelated plants of the division Anthocerotophyta. Living Ceratophyllum grows completely submerged, usually, though not always, floating on the surface, and does not tolerate drought....read more on Wikipedia.