hydrilla (Hydrilla verticillata)
ODA rating: A
Description
Perennial aquatic plant. Grows rooted to the bottom with long stems that reach water’s surface. Can be monoecious or dioecious. Leaves are 1/16 to 1/8 inch wide, 1/4 to 3/4 inch long and occur in whorls of five. Small, axillary leaf scales are found next to the stem and inserted at the base of the leaf, a character that distinguishes hydrilla from other family members. The nut-like turions (tubers) are a key identifying feature. Egeria densa is similar in appearence but has leaves in whorls of four and does not have turions.
Impacts
Hydrilla is the most serious threat to aquatic ecosystems in temperate climate zones. Dense stands of hydrilla provide poor habitat for fish and other wildlife altering water quality by raising pH, decreasing oxygen, and increasing temperature. Stagnant water created by mats provides good breeding grounds for mosquitoes. Hydrilla interferes with recreational activities such as swimming, boating, fishing, and water skiing and will clog irrigation ditches and intake pipes.
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Image courtesy of James R. Allison, Georgia Department of Natural Resources |
Image courtesy of Raghavan Charudattan, University of Florida
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If images are downloaded and used from the ODA web site please be sure to credit the photographer.
Introduction
Hydrilla was discovered in the United States in 1960 at two Florida locations, a canal near Miami and in Crystal River (Blackburn et al. 1969)
Distribution in Oregon
This species is not yet known to occur in Oregon, but does occur in Washington and California.
Map legend
Yellow: limited distribution in County
Red: abundant in County
Grey: not known to be present in County
Biological controls
Biological control agents are not used on "A" listed weeds in Oregon. If this weed is found in the state it will be managed for eradication or containment. Four approved biological control agents are available for control of hydrilla, but none of them are established in surrounding Pacific Northwest states.
Informational Links
WeedMapper
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