HYDRILLA

An exotic (nonnative) aquatic weed, hydrilla (Hydrilla verticillata) has come to represent a serious threat to lakes, reservoirs, streams and canals in the United States. A native of Asia, Africa, and Australia, hydrilla is part of a group of rooted aquatic plants well adapted to growth under water. Hydrilla was first introduced to the U.S. in Florida during the 1950s, probably for use in aquariums. Hydrilla is capable of prodigious growth, expanding from a few acres to several thousand acres in two to three years. Due to its ability to photosynthesize under very low light conditions, hydrilla becomes easily established in turbid waters and at greater depths than other aquatic plants. Most populations in the U.S. comprise dioecious female plants; reproduction is asexual, including fragmentation and the formation of hardy, long-lived propagules, called turions or tubers, which form deep in the sediment and remain viable for as long as ten years. Once hydrilla has invaded a site, the diversity of other rooted, submersed aquatic plants plummets, resulting in monospecific stands of hydrilla and loss of biodiversity. At is peak population, hydrilla has reduced water flows in canal systems by up to 80 percent and in small, standing-water impoundments, such as lakes and ponds, hydrilla can often completely cover the water surface within two to three years.