Elodea

Elodea canadensis Michaux.

Synonyms - Anacharis canadensis

Family: Hydrocharitaceae.

Names:

Elodea is from the Greek elodees meaning swampy and refers to the plants preference for shallow water habitats.
Canadensis refers to its country of origin, Canada.

Other names:

American Elodea
Canadian Pondweed
Oxygen weed
Waterweed

Summary:

A submerged, leafy, perennial, aquatic plant, rooted in the mud with single stems rising to a much branched top that forms dense dark green mats, just under the water surface. It is prolific in summer in water less them 5 m deep.

Description:

Cotyledons:

One.

Leaves:

Submerged. Overlapping. Lower ones, opposite. Upper ones in rings of 3 (rarely 6 or 12). Leaf sets crowded near the tips of stems and spaced up to 25 mm apart lower down. Axillary scales are circular in outline.
Petiole - None.
Blade - Dark green to brownish green, thin, soft, spreading or curled with a thin translucent edge. Lower ones, egg shaped. Upper ones oblong, 6-17 mm long x 0.2-5 mm wide. Usually have dark tipped, forward pointing, teeth on edges. Rounded tip. Tiny, single celled spines on the edges.
Sheath - None.

Stems:

Submerged, cylindrical, upward bending, flexible but brittle at the joints, to 3000 mm long. Hairless. Branches near top. Lateral branches are compact with short inter-nodes. Roots form at the nodes. Breaks at the joints. Dormant axillary buds (turions). Short, thin stolons are attached to the bottom mud.

Flower head:

Single flowers sticking out of a 10 mm long, 2 toothed, spathe that forms in the axils of upper leaves.

Flowers:

Male and female flowers on separate plants. Female plants not recorded in Australia. Flowers open at the water surface.
Ovary - 3 styles that are forked at the tip.
Perianth - Flower floats near the surface on a white thread-like extension of the perianth that is up to 300 mm long in the female and to 200 mm long in the male.
Sepals - 3, spreading, striped, 2-4 mm or more long. In the male flowers they are persistent and in the female flower they fall off as the flower opens.
Petals - 3, white, spreading, spoon shaped, narrower than sepals, 5 mm long.
Stamens - 9 in the male, 3 small staminodes in the female.
Anthers -

Fruit:

Not present in Australia.
Egg shaped to cylindrical, beaked, stalkless capsule, 6-9 mm long x 2-3 mm wide, with 1-3 seeds. Develops within the spathe that is usually submerged some distance below the water surface.

Seeds:

Doesn't produce seed in Australia because no female plants have been found.
Cylindrical, 4 mm long x 0.75 mm diameter, shortly beaked, partially hairy.

Roots:

Fine thread-like roots arising from the nodes of the short, thread-like stolons and at the lower nodes of the stems.

Key Characters:

Leaves in whorls of three. Finely toothed leaves.

Biology:

Life cycle:

Perennial. Growth starts in spring as water temperature exceeds 15 deg Celsius and forms a thick vegetative mat over summer occupying most of the water volume. Stolons creep along in the mud to send up new stems. Buds (turions) in stem fragments root into the mud and form new stems also. The stems grow towards the surface and branch profusely. Vigorous growth continues while temperatures are over 250C. Male flowers are present from November to January. As water temperatures fall, and day length decreases in winter, growth slows and it survives as semi dormant shoots or forms axillary buds (turions) covered by closely overlapping leaves. Many plants die in winter. Overseas, female flowers reach the surface before the male flowers and produce seed to survive the winter period.

Physiology:

Grows better where bicarbonate levels are high and reduced iron levels.
Prefers high light intensities of 7-30% of full sunlight. Prefers high and constant water temperatures with a optimum of 250C.

Reproduction:

In Australia all reproduction is by vegetative means.

Flowering times:

November to January.

Seed Biology and Germination:

Vegetative Propagules:

Stem fragments, stolons, dormant buds or turions.

Hybrids:

Allelopathy:

Population Dynamics and Dispersal:

Spread by fragments with roots. Seed is not produced in Australia. Fragments break off and are spread with water movement. Long distance spread is usually from sale of plants to aquarium owners who later dump them into the water ways.

Origin and History:

North America, Canada.
It was recorded in Victoria in 1949 and NSW in 1958 but was probably introduced much earlier.
Introduced into Tasmania in the 1960's.

Distribution:

NSW, TAS, VIC, WA.

Courtesy Australia's Virtual Herbarium.

Habitats:

Mild to warm fresh water bodies, 300-3000 mm deep. Rarely found in water deeper than 5000 mm. Prefers still or slow moving water but will tolerate fast moving water.

Climate:

Tropical, subtropical and temperate regions.

Soil:

Prefers muddy bottom channels and streams over sandy bottom areas.

Plant Associations:

Significance:

Beneficial:

Detrimental:

Serious weed of irrigation channels reducing flows by 60-80%. Limits the use of water bodies and significantly affects fish and aquatic life by changing the light, temperature, oxygen, pH and nutrient status of water bodies.
It interferes with hydro electric generators, town water supplies and irrigation systems.
It reduces the amenity value and navigability of rivers and streams.
It is one of the most persistent and obstructive water weeds.

Toxicity:

Not recorded as toxic.

Legislation:

Noxious weed of NT, SA, Tas, WA.

Management and Control:

Mechanical removal provides temporary relief. Lowering water levels is only effective if the bottom mud can be dried out. Shading channels with vegetation on banks helps reduce Elodea growth rate. Reducing nutrients or temperature and increasing turbidity also reduces growth. Maximum growth occurs at 25 degrees Celsius. Water temperatures below 5 degrees Celsius control it. It will survive over winter in moist mud or silt. It is extremely difficult to eradicate. Acrolein is used by licensed operators for control. Triazine herbicides are used in still water situations. Terbutryn is probably the most useful. A sulfonyl urea herbicide bensulfuron methyl is showing promise. Diquat is useful where water needs to be used soon after treatment.

Thresholds:

Eradication strategies:

Herbicide resistance:

Biological Control:

Biological control programs are used in other countries but are unsuitable for Australia.

Related plants:

None.

Plants of similar appearance:

Hydrilla has 4 to 8 leaves in each whorl and deeper serrations on the leaf margins.
Leafy Elodea (Egeria densa) has leaves in whorls of 3-6.

References:

A.P.B. Advisory Leaflet No. 42 (1979)

Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P26. Photo.

Ciba Geigy (1982) Grass Weeds 3. CIBA GEIGY Ltd, Basle, Switzerland. P89. Diagrams.

Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P44-45. Photo.

Hyde-Wyatt, B.H. and Morris, D.I. (1980) The Noxious and Secondary Weeds of Tasmania. (Tasmanian Department of Agriculture, Hobart, Tasmania).P114-115. Diagrams.

Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).

Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #492.1.

Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious weeds of Australia. (Inkata Press, Melbourne). P64-67. Photos.

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.