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Hydrilla verticillata

Hydrilla has whorls of tiny toothed leaves along long, freely branching stems.
Hydrilla has whorls of tiny toothed leaves along long, freely branching stems.

Hydrilla is an invasive bay grass that grows in freshwater portions of the Chesapeake Bay and most of its tributaries.


Hydrilla is made up of long, freely branching stems with tiny, straight or lance-shaped leaves that usually have visible teeth along the edges. Leaves grow in whorls of 4 to 5 along each stem. Tiny, white flowers appear in late summer. Rhizomes grow along or just below bottom sediments. Roots and small, fleshy tubers grow from the rhizomes.


Grows in fresh waters, but has been found in brackish waters. Does not need as much light as other bay grasses, so it can grow in more turbid areas.


Common in the upper Chesapeake Bay and in most freshwater tributaries. Native to Africa, Australia and parts of Asia.


Migratory waterfowl feed on hydrilla.

Reproduction and Life Cycle:

Asexual reproduction takes place when plant fragments, tubers, roots and turions develop into new plants. Sexual reproduction occurs in late summer, when pollen from male flowers fertilizes female flowers. The seeds that form have about a 50 percent chance of growing into new plants.

Other Facts:

  • Hydrilla was introduced to the U.S. in the 1960s through the aquarium trade. It was first detected in the Potomac River near Washington, D.C., in 1982. By 1992, it covered 3,000 acres of the river.
  • It is considered by some to be a nuisance because it can block boating channels and limit water sports
  • Hydrilla has become an excellent habitat for fishes, particularly largemouth bass
  • It can be confused with common waterweed. You can distinguish hydrilla by its whorls of 4 to 5 leaves, the visible teeth along the edges of its leaves and its fleshy tubers.

Sources and Additional Information:


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