Practical information to identify and manage non-native, invasive plants and animals
The Quiet Invasion:A Guide to Invasive Species of the Galveston Bay Area
Hydrilla verticillata
| USDA Symbol: | HYVE3 |
| ITIS TSN: | 38974 |
| Presence: | Current Invaders |
| Habitat: | Aquatic |
| Native Range: | Southern India for the dioecious form (having male and female flowers on different plants); Korea for the monoecious form (having male and female flowers on the same plant) |
Toxic Characteristics
This species is not known to be toxic.Geographic Distribution
Most common in the southeastern United States, California, and Arizona, but also reported in the Northeast and Washington in the West. Hydrilla exists in Texas reservoirs and waterways from north-central and eastern Texas south to the Rio Grande.Introduction Pathways
Introduced to Florida via the aquarium trade in Tampa and Miami; first discovered in waterways in 1960. Quickly spread and continues to spread by boat traffic which fragment and disperse plant parts.Specific Primary Habitats
Invades both freshwater and brackish water environments. Tolerates water depths from a few inches to more than 20 feet, as well as low to high nutrient environments. Tolerates very low light conditions.Identifying Characteristics
Rooted in hydro-soil, grows as a submerged underwater plant. Stems branch extensively at the water surface. Leaves are 5/8 inches long, saw-toothed, and yellow-green to green, depending on light exposure. They grow in groups of four to eight in a whorled arrangement around the thin stems. Female flowers (translucent) float on the surface, attached to leaf axils by a thin stalk; male flowers (white to red) break free and float to the surface.Reproduction Characteristics
Commonly reproduces from fragmented stems which readily regrow, forming new clones of the original plant. New shoots also bud from leaf axils (where petioles attach to the stem) as well as from subterranean tubers.Growth Characteristics
Hydrilla can grow up to 1 inch in a day and stems can reach 30 feet in length. Stems grow until they reach the water surface, filling the entire water column.Ecological, Economic, or Social Impact
Dense underwater stands of hydrilla raise water pH and temperature, and lower dissolved oxygen. While the number of fish is often increased, large fish become more rare. Promotes mosquito habitat. Potentially affects power generation by clogging dams.Control
Avoid introducing this plant to local waterways. Fluridone (slow-acting), endothall (fast-acting), and copper compounds are all EPA-registered herbicides which require repeated applications. An opaque soil covering is recommended around docks. Mechanical removal encourages spread and is not recommended.General Notes
Elodea canadensis is an native alternative in many other states, but its range is not reported to extend into Texas.|
Native Species Alternatives
Below is a list of alternative plants that are native to the area:
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Lists
This species belongs to the following lists:
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Images
To view a larger version of an image, click on the thumbnail. Close-up of saw-toothed leaves of Hydrilla. Photo courtesy of Jon Rodgers. |
 Close-up of stem tip and leaves of Hydrilla. Photo courtesy of Jon Rodgers. |
 Stems of Hydrilla. Photo courtesy of Jon Rodgers. |
 Hydrilla invading Lake Conroe, Texas. Photo courtesy of Earl Chilton, Texas Parks and Wildlife Department. |
 Hydrilla mat covering the surface of the water on Lake Conroe, Texas. Photo courtesy of Earl Chilton, Texas Parks and Wildlife Department. |
 Hydrilla mat along the shore of Lake Conroe, Texas. Photo courtesy of Earl Chilton, Texas Parks and Wildlife Department. |