Appearance

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 four or five 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.

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.
• 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 four to five leaves, the visible teeth along the edges of its leaves and its fleshy tubers.

Sources and Additional Information

• Underwater Grasses in Chesapeake Bay & Mid-Atlantic Coastal Waters by Maryland Sea Grant
• Life in the Chesapeake Bay by Alice Jane Lippson and Robert L. Lippson
• Chesapeake Bay: Nature of the Estuary, A Field Guide by Christopher P. White
• Bay Grass Key: Hydrilla – Maryland Department of Natural Resources
• Invasive Alien Plant Species of Virginia: Hydrilla – Virginia Department of Conservation and Recreation
• Plant Invaders of Mid-Atlantic Natural Areas: Hydrilla – U.S. Fish & Wildlife Service
• PLANTS Database: Hydrilla verticillata – USDA Natural Resources Conservation Service