hydrilla (Hydrilla verticillata), submerged aquatic plant that is the sole member of the genus Hydrilla in the frog’s-bit family (Hydrocharitaceae). Hydrilla is possibly native to Africa or Europe but has naturalized in lakes and streams around the world. Brought to North America in the 1950s, the plant has become a troublesome aquatic weed, as its vast carpets of tangled vegetation can clog the intake valves of power plants and water installations and have significantly impacted biodiversity.
Hydrilla is a hardy, fast-growing, herbaceous perennial with long, slender stems that can grow to some 7 metres (23 feet) in length. The leaves grow in pairs or in whorls of three to eight and are small, lance-shaped or oblong, and distinctly toothed. Individuals can be either monoecious (bearing both male and female flowers) or dioecious (bearing only male or female flowers). The tiny male flowers are released from the plant and fertilize the female flowers they drift into contact with. However, the plant primarily reproduces asexually using stem fragments, rhizomes, stolons, and turions (budlike vegetative propagules).