Hydrilla
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: Hydrocharitaceae (Tape grass family)
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
Identification
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.
Similar Species
Exotics: Egaria densa
Natives: Elodea canadensis
Impacts
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. Beleaved to have been brought to Florida in the 1950’s for use as an aquarium plant.
Biology/ Ecology
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
References
Aquatic, Wetland and Invasive Plant
Particulars and Photographs
University of Florida, Center for Aquatic and Invasive Plants
http://aquat1.ifas.ufl.edu/hyvepic.html
Non-Native Invasive Aquatic Plants in the United States
Center for Aquatic and Invasive Plants, University of Florida and Sea Grant
http://plants.ifas.ufl.edu/seagrant/hydver2.html
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