Hornwort, known scientifically as Ceratophyllum demersum, is a dark green, rootless aquatic plant that forms bushy, branched masses suspended in the water column. Frequently called coontail, it thrives worldwide in lakes, ponds, and still or slow-moving waterways. The forked, horn-like leaves of Ceratophyllum demersum capture light efficiently and create dense thickets used by fish for shelter and spawning.

Remarkably, the plant produces allelopathic compounds that can suppress algae and competing vegetation. It spreads through fragmentation and also forms overwintering buds that sink and regrow as conditions improve. These traits allow Ceratophyllum demersum to colonize habitats quickly and endure seasonal shifts. Its ability to float freely without anchoring makes it one of the most recognizable and adaptable freshwater species.