Hydrilla verticillata (hydrilla).
Abstract H. verticillata is a submerged fast-growing aquatic herb. It has a highly effective survival strategy that makes it one of the most troublesome aquatic weeds of water bodies in the world. It has the potential to alter fishery populations, cause shifts in zooplankton communities and affect water chemistry. It forms dense masses, outcompeting native plants and interfering with many uses of waterways. It is readily dispersed by movement of plant fragments and can produce up to 6,000 tubers per m2. Tubers can remain viable for several days out of water or for over 4 years in undisturbed sediment. They are not impacted by most management activities, and a small percentage can sprout throughout the year making the species very difficult to manage or eradicate. It can be spread by water flow, waterfowl and recreational activities and is sold as an aquarium plant. Currently, this species is considered as one of the most aggressive invasive species in aquatic habitats. In the USA it has been listed as a Federal Noxious Weed since 1976, and is regarded as one of the worst invasive aquatic weed problems in Florida and much of the country. Its import is prohibited in Western Australia and Tasmania, and it is on the EPPO alert list.