Cornell Cooperative Extension

Schoharie and Otsego Counties
Infestation of Hydrilla verticillata discovered in the Crystal River in south Florida in 1960.
Image by Raghavan Charudattan

Hydrilla over takes a pond

Hydrilla Infestation, USDI National Park Service
Image by Tony Pernas, USDI National Park Service, Bugwood.org

Hydrilla infestation by Tony Pernas, USDI National Park Service, Bugwood.org

Hydrilla Plant
Image by Robert Vidéki, Doronicum Kft., Bugwood.org

Hydrilla close up by Robert Vidéki, Doronicum Kft., Bugwood.org

Hydrilla

The highly invasive aquatic plant, Hydrilla verticillata, commonly known as 'hydrilla' or 'water thyme' was found in the Cayuga Inlet in 2011. The biotype that was found in the inlet is native to southeast Asia and was brought to the United States through the aquarium trade. Hydrilla was first found in the wild in Florida in the 1950's. It has since spread to many parts of the US. We will never know how hydrilla arrived in the Cayuga Inlet, but it was probably spread by a boater or someone dumping an aquarium irresponsibly.

Last updated July 13, 2020

Hydrilla

Monoecious / Dioecious

Hydrilla has both dioecious and monoecious biotypes. Dioecious plants have separate reproductive units; individuals are either male or female and cannot self-fertilize. Whereas, monoecious is classified by each indiviual having both reproductive units that are merely female and reproductive units that are merely male.

The dioecious has female flowering plants and originated in Southern India. It was often used in aquariums and probably dumped in Miami and Tampa in the 1950's. From there it has spread and is found in much of the Southern US.

Monecious hydrilla is thought to have originated in Korea and was introduced in the US decades later then the dioecious strand in the Potomac Basin and now spans north from South Carolina.

View a map of hydrilla throughout the United States.

Source: Center of Aquatic and Invasive Plants, University of Florida, IFAS

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Federal Noxious Weed

Hydrilla verticillata is found on the USDA's Federal Noxious Weed List and is regulated by strict permits.

It is illegal to sell/buy hydrilla. However, many sales occur due to misidentification of the plant and/or contamination of legal sales. Being that it looks a great deal like elodea, which is commonly sold as an aquarium plant as well, people sometimes mistake one plant for the other and mis-lable it, or, a stray piece of hydrilla will get packed along with a shipment of elodea.