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!

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.

Seedling

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. Believed 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