Hydrilla, or Hydrilla verticillata, is a submerged freshwater plant with long stems lined by serrated, whorled leaves that create a textured, slightly spiny appearance underwater. Native to parts of Asia, Hydrilla verticillata has become one of the most aggressive aquatic invaders in the world. It tolerates low light, low nutrients, and variable water chemistry, thriving where many species cannot.

A defining strength of Hydrilla verticillata is its multi-mode reproduction: it spreads through fragments, tubers, stolons, and turions, ensuring survival even after mechanical disturbance. Dense growth forms thick underwater canopies that restrict light, reduce oxygen, and block native plants. Its ability to fill the entire water column gives it immense ecological influence and makes it one of the most challenging aquatic species to manage.