Hornwort

Myriophyllum is a genus of aquatic plants in the family Haloragaceae, widely distributed across temperate to tropical lakes and rivers on every continent. Commonly called water milfoil, the genus is characterized by whorled leaves intricately pinnated into hair-like segments, producing a feathery, plume-like appearance that sways gracefully in aquarium water flow. Multiple species are traded for aquarium use, most notably M. mattogrossense and M. tuberculatum, which vary in leaf color from green to red and in cultivation difficulty. Some species have a long history in goldfish aquaria due to their tolerance of alkaline, hard water. CO2 supplementation promotes more vigorous growth in planted aquarium conditions. Root systems are absent or reduced in some species, which are planted directly in substrate or allowed to float. Several species have become invasive in natural waterways following aquarium release, leading to import restrictions in certain regions.

Source: Wikipedia (CC BY-SA 4.0)

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