Hydrilla verticillata: Biology and
Ecology
By: Carey Minteer - University of Arkansas
Background
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Native of southeast Asia
Introduced into the United States in 1955
Federal noxious weed
Since 1983 Hydrilla has been the most
abundant submerged plant in Florida
(McCann et al, 1996)
More Background
• Plants can be monoecious or dioecious
(Van Driesche, 2002)
• Populations in the southeastern United
States are dioecious and entirely female.
• Plants spread through vegetative
regeneration.
• Monoecious strain found in Potomac river
(Steward et al., 1984).
Monoecious strain
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Spreading down the Potomac river.
Sexual reproduction can occur.
Pollination occurs on the water’s surface
Pollen is released from free floating male
flowers and “caught” by the free floating
female flowers (Cronk and
Fennessy,2001).
Vegetative reproduction
• Subterranean tubers
• Axillary turions
• Fragments
Subterranean Tubers
• Sometimes buried
several centimeters
below the surface.
• Can sprout new
shoots even after a
period of 4 years.
• In Florida canal there
are an average of 918
turions per m-2
(Sutton, 1996).
Tim Murphy, University of Georgia, Bugwood.org
Axillary Turions
• Turions form in the leaf axils at the ends of
the stems.
• Turions abscise and fall into the sediment.
• Over winter and produce new growth in
the spring.
Fragmentation
• Spread from lake to lake
by boats.
• Large populations found
adjacent to boat ramps.
• Spreads extremely fast
• Total lake coverage can
change drastically in just
a years time.
Raghavan Charudattan, University of Florida, Bugwood.org
Biology
• Monocot
• Family: Hydrocharitaceae
• Rooted submerged
perennial
• Leaves 5-15 mm long
and 2-4 mm wide
• Leaves arranged in pairs
on lower nodes.
• Leaves in whorls of 3-10
on the upper nodes.
More Biology…
• Stems vary in length
from a few
centimeters to several
meters.
• Three types: erect,
horizontal, or
subterranean.
• Erect stems support
branches, leaves, and
flowers.
Chris Evans, River to River CWMA, Bugwood.org
Habitat
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Sunny
Sandy substrate
Low levels of rock
Grows in depths
between 0.7m and
2.4m
• Has been shown to
grow in depths of up
to 15m.
Raghavan Charudattan, University of Florida, Bugwood.org
Habit
• Apical growth
• Several erect stems form
at a single node of a
horizontal stem
• Branches form a canopy
• 70% of biomass
concentrated at the
water’s surface (Cronk
and Fennessey, 2001).
Carey Minteer, University of Arkansas
Distribution
http://www.eddmaps.org/distribution/subdist.cfm?sub=3028
Effects on Native Vegetation
• Hydrilla forms lush canopies, that shades
native vegetation.
• Alters seed banks
• Allelopathic
• Shown to inhibit the growth of
Ceratophyllum demersum (coontail)
(Schmitz et al., 1993).
Effects on Animals
• Dense stands provide refuge for young
fish.
• High survival rates leads to over
population and stunted fish growth.
• Predator fish cannot forage as well.
• Numbers and biomass of these predatory
fish decline.
Effects on Human Activities
• Hydrilla reduces open
water feeding and
spawning areas of sport
fish
• Clog boat motors
• Thick mats can hinder
irrigation by as much as
90% (CDFA,2000).
• Hydroelectric power is
hindered by
fragmentation of plant
material
Wilfredo Robles, Mississippi State University, Bugwood.org
More to come…
• Control of Hydrilla
• Biological, mechanical, chemical.
Literature Cited
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California Department of Food and Agriculture.2000a. ` Hydrilla program 20.20.1,
Program statement 2000 season, fiscal year 200/2001. Plant Health and pest
prevention services, Integrated pest control branch, Sacramento, CA.
Cronk, J. and M. Fennessy. 2001. Wetland plants. Biology and Ecology. CRC Press
LLC, NY.
McCann, J.A,, Arkin, L.N., and Williams, J.P. 1996. Nonindigenous aquatic and
selected terrestrial species of Florida. Orlando, University of Florida, Center for
aquatic plants website. http://aquat1/ifas.ufl.edu/mctitle.htm
Schmitz, D.C., Schardt, J.D., Leslie, A.J., Dray, F.A., Osborne, J.A., and Nelson,
B.V.1993. The ecological impact and management history of three invasive alien
aquatic plant species in Florida. Biological pollution: The control and impact of
Invasive exotic species. B.N. McKnight, Ed. Pp 173-194. Indianapolis, Indiana
Academy of Science.
Steward. K.K., Van, T.K., Carter,V., and Pieterse,A.H. 1984. Hydrilla invades
Washington D.C. and the Potomac. American Journal of Botany 71:162-163.
Sutton, D.L. 1996. Depletion of turions and tubers of Hydrilla verticillata in the North
River canal, Florida. Aquatic Botany53:121-130.