Hydrilla

• Hydrilla asiatica
• Hydrilla japonica
• Hydrilla lithuanica
• Hydrilla ovalifolica
• Hydrilla verticillata

Hydrilla is an aquatic plant, it is native to the warm waters of Asia, Africa and Australia.

Plants may be monecious or dioecious and can reproduce vegetatively by fragmentation and by tubers and turions (overwintering buds).

Hydrilla verticillata became an aquatic weed in the United States in the 1960's following release from aquariums into Florida's waterways. By the 1990s hydrilla was well-established in the southern states where control and management costs millions of dollars each year. Infestations of Hydrilla verticillata have also been detected in California and Washington. Hydrilla has been spotted as far North as Maryland and Delaware.

File:Hydrillainfestation.jpg

Infestation of Hydrilla verticillata in the Crystal River, South Florida, 1960

Hydrilla can be controlled by the application of aquatic herbicides and it is also preferred by grass carp. Tubers pose a problem to control as they can lay dormant for a number of years.

Hydrilla is cumbersome for fisherman, swimmers, and watersports. The economic impact on recreational areas is estimated to be in the millions of dollars.

Hydrilla verticillata closely resembles two aquatic plants: Brazilian elodea (Egeria densa) and native American waterweed (Elodea canadensis).

• Hydrilla has tubers that are 0.2 to 0.4 inch long, off-white to yellowish, that are burried in sediments.
• Leaves are arranged in whorls around the stem (generally five leaves per whorl).
• There are serrations or small spines along the leaf edges.
• The midrib of the leaf is often reddish when fresh.