Hydrilla
Hydrilla verticillata

Hydrilla is a nonnative underwater grass that grows in freshwater portions of the Chesapeake Bay and most of its tributaries. It has long, branching stems with small, straight or lance-shaped leaves.

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Branch of hydrilla growing underwater with tiny white spots on it that are flowers.
Hydrilla leaves come in whorls of five, though some may have four. The leaves have teeth that are easily visible. (Photo courtesy of joel_p_ashman/iNaturalist CC BY-NC, cropped and toned)

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Appearance

Hydrilla is made up of long, freely branching stems with tiny, straight or lance-shaped leaves. Leaves usually have visible teeth along the edges. Leaves grow in whorls of four or five along each stem.

Tiny, white flowers appear in late summer. The underground portion of the plant’s stem called rhizomes grow along or just below bottom sediments. Roots and small, fleshy tubers grow from the rhizomes.

Predators

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% chance of growing into new plants.

Did you know?

  • 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.
  • Hydrilla does not need as much light as other bay grasses, so it can grow in more turbid areas.
  • 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 and migratory waterfowl feed on the plant.
  • It can be confused with common waterweed. You can distinguish hydrilla by its whorls of four to five leaves, the visible teeth along the edges of its leaves and its fleshy tubers.

Sources and additional information

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