| SOURCE: The following information on this
species is taken from the Delaware River Invasive Plant Partnership, Invasive
Plant Fact Sheets at http://www.paflora.org/DRIPP.html.
Modifications include additional pictures (from www.invasives.org
and http://aquat1.ifas.ufl.edu/hyvepic.html)
and resource information. Check the website link for future updates. The last
update for this fact sheet is March 2004. |
DESCRIPTION:
Hydrilla is a rooted submergent aquatic that forms dense mats in still or
slowly moving water. Small whitish tubers are produced on the roots late in the
growing season. Hydrilla is very similar to the native waterweeds (Elodea
canadensis and E. nattallii). The most obvious differences are
the 4-8 visibly toothed leaves per node on hydrilla and the presence of tubers.
Waterweed leaves occur in whorls of 3 and have a smooth edge; tubers are not
produced. Brazilian waterweed (Egeria densa), another non-native species
in the Frog's-bit Family that is established in Pennsylvania, is also similar.
Its leaves, in whorls of 4-8, are very finely toothed and crowded so that those
from one whorl overlap the leaves from adjacent nodes. Brazilian waterweed does
not produce tubers.
Height
- The stems are 1 to many feet long, depending on the depth of the water.
Stem
- Stems are slender and flexible, branching mainly near the water surface, and
are nearly covered by the whorls of leaves. The stems are rooted at the base;
in addition, adventitious roots may form at the nodes.
Leaves
- Leaves are narrow and sharply toothed; they are arranged on the stem in
whorls of 4-8 eaves at each node. The leaves are about as long as the space
between nodes and do not overlap adjacent whorls of leaves.
Flowers
- Flowers are solitary and unisexual; the female flower is white with 3 petals
and 3 sepals, it is borne on a long slender pedicel that reaches the water
surface. Male flowers are released and float to the surface of the water; they
have 3 tiny stamens.
Fruit and seed
- Fruits are cylindrical and contain up to 5 seeds.
 |
Photo: Raghavan Charudattan, University of Florida,
www.forestryimages.org
|
DISTRIBUTION
AND HABITAT: The precise area of origin of hydrilla is not known, it is variously listed
as Asia, Africa, and perhaps Australia. It grows in water from 1-12 feet deep
depending on the clarity. Hydrilla is tolerant of various pollutants and a
range of water chemistry. In Pennsylvania it is known from only a few sites in
the eastern part of the state (PA Flora Database 2004).
EFFECTS OF
INVASION: Hydrilla is a major aquatic weed throughout the southeastern United States;
thick mats of hydrilla interfere with navigation, clog water intake screens,
and hamper recreational boating. Hydrilla also competes with native submergent
aquatic vegetation. Annual control efforts in Florida alone cost millions of
dollars. It was designated as a federal noxious weed in 1979, and is identified
in noxious weed laws in FL, LA, CA, TX, SC, NC, OR, WA, and AZ.
 |
 Photo:
Raghavan Charudattan, University of Florida,
www.forestryimages.org
|
REPRODUCTION
AND METHODS OF DISPERSAL: As with many aquatic plants, hydrilla employs vegetative means
of propagation very effectively. Living stem sections may break off and float,
providing one means of dispersal. Even a small stem section containing a single
node can produce adventitious roots and initiate a new colony. Modified stems
called stolons form in the substrate and also serve as a means of vegetative
spread. Late in the season whitish tubers form at the ends of the stolons;
these tubers are resistant to herbicide treatment and allow for rapid
recolonization of treated sites. Seed production appears to be minimal in our
area.
NATIVE ALTERNATIVES
FOR LANDSCAPE USE: Native species of waterweed (Elodea canadensis and E. nuttallii)
should be encouraged in place of hydrilla.
AUTHORS:
Ann F. Rhoads and Timothy A. Block, Morris Arboretum, University of
Pennsylvania.
For more information
on hydrilla, please contact:
Cornell University, Biological Control of Weeds, Hydrilla,
http://www.invasiveplants.net/invasiveplants/biologicalcontrol/default.asp
Hydrilla chapter from Langeland/Burks book, Identification & Biology of
Non-Native Plants In Florida's Natural Areas Invasive Plant Atlas of New
England, http://invasives.eeb.uconn.edu/ipane/
Mid-Atlantic Exotic Pest Plant Council, Inc., http://www.ma-eppc.org
National Invasive Species Information Center,
http://www.invasivespeciesinfo.gov
Plants Invaders of Mid-Atlantic Natural Areas,
http://www.nps.gov/plants/alien/pubs/midatlantic/
Southeast Exotic Pest Plant Council; Invasive Plant Manual,
http://www.se-eppc.org/manual/
The Bugwood Network, MA-EPPC Plant List,
http://www.invasive.org/maweeds.cfm
The Nature Conservancy Invasive Species Initiative,
http://tncweeds.ucdavis.edu/esadocs.html
USDA - NRCS PLANTS Database, http://plants.usda.gov/
USGS Nonindigenous Aquatic Species Fact Sheets,
http://nas.er.usgs.gov/plants/docs/hy_verti.html
University of Florida, Center for Aquatic and Invasive Plants,
http://aquat1.ifas.ufl.edu/hyvepic.html
University of Florida Cooperative Extension Service booklet, Hydrilla circular
Virginia Natural Heritage Program Fact Sheet - Hydrilla;
http://www.dcr.virginia.gov/dnh/invlist.htm
REFERENCES:
Batcher, M.S. Element Stewardship Abstract for Hydrilla verticillata (L.f.)
Royle. http://tncweeds.ucdavis.edu/esadocs/documnts/hydrver.pdf. Pennsylvania
Flora Database, http://www.paflora.org
Van Driesche, R., R. Reardon. B. Blossey, S. Lyon, and M. Hoddle. 2002.
Biological Control if Invasive Plants in the Eastern United States.
FHTET-2002-04. United States Department of Agriculture, Forest Service,
Morgantown, WV.
Management and
Control Information
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