Hydrilla verticillata
Water thyme
HISTORY
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Origin – Possibly Africa, Asia,
India, or Austrailia
Introduced into Florida 1950’s
for aquarium use – dioecious
strain
Appeared in the Patomac
drainage in the 1970’s –
monecious strain
Has become the most
expensive aquatic plant control
project in the southeastern US
DISTRIBUTION
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Since introduction, has spread
to 690 bodies of water in 190
drainages in 21 states
Is present in Pennsylvania:
Schuylkill River, downtown
Philly
Lake Nockamixon – SW Pa
Highland Lake – Bradford Co.
PHYSICAL DESCRIPTION
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4-8 leaves in whorls around stem –
leaf margins saw-toothed
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Rooted – stems to 25’ long
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Profuse branching at the surface
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Produces both male and female
flowers
Is sometimes mistaken for the
native plant Elodea canadensis
GROWTH & REPRODUCTION
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Prolific reproducer – broken
stems, seeds, turions, and tubers
Can grow in any fresh water or
sea water with a salinity of 7%
South – overwinters as perenial
North – overwinters as tuber and
regrows from there
Can grow in 1% of full sunlight
CONTROL
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$5 million to control 7,600ha in
Florida
US Army Corps of Engineers $1 million to suppress hydrilla
in Jacksonville Distric and
$400,000 to supress in Lake
Seminole
Grass carp have been
introduced as a control agent
Asian Hydrilla Leaf Mining Fly
Hydrilla tuber weevil
POSITIVE ASPECT
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Has been discovered to be a biological remediation agent
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Shown to be capable of removing dissolved lead from a waterway
REFERENCES
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http://www.ecy.wa.gov/Programs/wq/plants/weeds/hydrilla.html
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http://edis.ifas.ufl.edu/IG120
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http://www.invasive.org/eastern/biocontrol/7Hydrilla.html
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http://www.dcnr.state.pa.us/Forestry/invasivetutorial/hydrilla.htm
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http://plants.ifas.ufl.edu/images/hydver/elocanc1.jpg
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http://plants.ifas.ufl.edu/node/183
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http://plants.usda.gov/java/profile?symbol=HYVE3
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http://nas.er.usgs.gov/taxgroup/plants/maps/Hy_verti_distr_us_Dec_03_web.JPG
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http://nas.er.usgs.gov/taxgroup/plants/docs/hy_verti.html
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http://cat.inist.fr/?aModele=afficheN&cpsidt=13903888
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http://www.erie.psu.edu/seagrant/publications/fs/Hydrilla.pdf