Hydrilla verticillata (L. f.) Royle
Keys to Identification
- Hydrilla is an aquatic weed that has the potential of impacting our waterways and agricultural water supplies. Hydrilla has not yet been found in Colorado.
Family: Tape grass (Hydrocharitaceae)
Other Names: waterthyme, Florida elodea
USDA Code: HYVE3
Legal Status: Colorado Noxious Weed List A
New in Colorado – call your county weed supervisor if you find this plant!
photo courtesy of USDA APHIS
Lifecycle: Perennial aquatic
Growth form: Forb/herb
Flower: Female flowers tiny and white, with 6 petals. Male flowers tiny greenish, closely attached to the leaf axle
Seeds/Fruit: Yellowish turions ("potato-like" tubers). Can remain viable for 4 years.
Leaves: Leaves are small, pointed and arraigned in whorls of 4-8 along the stem. Leaf margins are distinctly saw toothed.
Stems: Submersed stems are long and slender that branch profusely at the water surface. Stem fragments are one means of reproduction
Roots: Roots in the hydro soil, adventurous roots are white.
Other: This plant is noticeable rough when pulled through the hand. Southern populations (US) overwinter as perennials; northern populations overwinter and regrow from tubers.
Exotics: Egaria densa
Natives: Elodea canadensis
Agricultural: Could severely impact the Colorado’s system of water delivery (irrigation ditches and canals).
Ecological: Can grow in natural water bodies displacing native plants.
Other: In the South hydrilla impacts the recreational use of water bodies for boating, fishing and swimming. Major infestations limit sport fish size and weight.
Habitat and Distribution
General requirements: Aquatic plant. In Russia hydrilla grows as far north as 50° N Latitude (the equivalent of the USA/Canadian Border)
Distribution: Arizona, Atlantic Coast States to Connecticut (Excluding; New Jersey and New York), California, Gulf Coast States and Tennessee. No infestations of this plant have been documented in Colorado.
Historical: Dioecious type native to India, monoecious plants native to Korea. Believed to have been brought to Florida in the 1950’s for use as an aquarium plant.
Life cycle: Perennial
Mode of reproduction: Mainly plant fragments and turions (vegetative structures)
Seed production: Minimal
Seed bank: Unknown
Dispersal: Water movement, animals, man, recreation, equipment
Aquatic, Wetland and Invasive Plant
Particulars and Photographs
University of Florida, Center for Aquatic and Invasive Plants
Non-Native Invasive Aquatic Plants in the United States
Center for Aquatic and Invasive Plants, University of Florida and Sea Grant