Ceratophyllum demersum

Ceratophyllum demersum, commonly known as hornwort (a common name shared with the unrelated Anthocerotophyta), rigid hornwort, coontail, or coon's tail, is a species of flowering plant in the genus Ceratophyllum. It is a submerged, free-floating aquatic plant, with a cosmopolitan distribution, native to all continents except Antarctica. It is a harmful weed introduced in New Zealand. It is also a popular aquarium plant. Its genome has been sequenced to study angiosperm evolution.