The Hydrilla is a submersed plant native to Africa and Southeast Asia, a major aquatic weed throughout most of the world’s warmer climates introduced to into Florida in the early 1950s. By the 1990s it occupied more than 140,000 acres of public lakes and rivers. Due to an intensive management program, it has been reduced to under 50,000 acres.

Once the Hydrilla is established, it produces reproductive tubers numbering in the millions per acre in the soils of Florida waterways. The tubers still impact nearly 140,000 acres and represent potential regrowth if not continually managed immediately after sprouting. A method to prevent or minimize tuber formation has not been discovered.

Its leaves are submerged; in whorls of 3 to 1, 2-4 mm (0.1-0.2 in) wide and 6-20 mm (0.2-0.8 in) long, bearing course (visible) teeth along the margins and usually 1-4 small conical bumps along the underside of the midrib, which is often red. The stems are slender with much branching and up to 10.6 m (35 ft.) long; eventually form dense tangled masses at the water surface. The female flowers solitary, on long stalks, with three sepals and three petals, each about 4 mm (0.3 in.) long, whitish or translucent, floating at the water’s surface. Other characteristics include two types of special vegetative propagules: turions – fattened leaf buds at stem nodes, green, about 1.25 cm (1/2 in) wide; tubers – small (to 1cm long), off-white, swollen ends of underground stems.

The Hydrilla can grow an inch or more per day and can be found in water only a few inches deep in the deepest parts of Florida’s lakes and rivers. Entire waterbodies are covered within only one to two years due to its dense canopies are established. They quickly disperse throughout a waterway by stem fragments, buds, runners and tubers.

The Hydrilla has been known to cause the following environmental damage:

  • Canopies lower dissolved oxygen concentrations, reducing aquatic life
  • Decay doubles the amount of sediments that accumulate in a water body
  • Dense infestations can restrict water flow resulting in flooding along rivers and canals
  • Canopies produce ideal breeding environments for mosquitoes
  • Dense canopies shade out native submersed vegetation lowering biodiversity
  • Infestations restrict recreational activities such as boating, swimming, and fishing

Due to its aggressive growth rate, never transplant Hydrilla from waterway to waterway. Clean all boats and trailers live wells and diving gear of plant material before entering or leaving a waterbody. Possession of Hydrilla is illegal in Florida without a special permit.

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