Pormenor da flor.

Elodea canadensis

Small aquatic perennial herb.

Scientific name: Elodea canadensis Michx.

Common names: Canadian pondweed, common elodea, Canadian waterweed, American elodea, broad waterweed

Family: Hydrocharitaceae

Status in Portugal: invasive species (listed in the annex I of Decreto-Lei n° 565/99, of 21 December)

Risk Assessment score: (in development)

Synonymy: Anacharis canadensis (Michx.) Planch., Anacharis canadensis (Michx.) Planch. var. planchonii (Caspary) Victorin, Elodea brandegeeae St. John, Elodea ioensis Wylie, Elodea linearis (Rydb.) St. John, Elodea planchonii Caspary, Philotria canadensis (Michx.) Britt., Philotria linearis Rydb.

Last update: 08/07/2014

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How to recognise it

Perennial aquatic herb, dark green, with thin stems and a fragile look.

Leaves: 5-12 x 1-2 mm, rarely larger, generally linearoblong, obtuse, finely serrate on the 2/3 distal, frequently 3 on each node.

Flowers: rarely produced; male and female flowers occur on different plants; 3 green sepals, purple-striated; withe petals, narrower than sepals, 5 (6) mm long; 9 yellow stamens.

Frutos: capsules with 6-9 mm, with 3-4 seeds inside.

Flowering: May to August.

 

Similar species

Egeria densa Planch. is very similar, distinguishing itself by its robustness and size – the leaves are normally longer than 2 cm and they appear (at least the superior ones) with more than 3 in each node. The flowers of Egeria densa are also larger, with petals on male flowers up to 12 mm long. According to some references, E. densa, presents a larger extension in Portugal.

 

Characteristics that aid invasion

It propagates vegetatively by stem fragmentation. Each fragment may be dragged by the water flow and originate new invasion foci far from the original population.

It also reproduces by seed, though less frequently.

 

Native distribution area

North America.

 

Distribution in Portugal

Mainland Portugal (Beira Litoral).

Geographic areas where there are records of Elodea canadensis

 

Other places where the species is invasive

Europe (United Kingdom, Ireland, Czech Republic, Germany, France, Denmark, Finland, Norway, Poland, Spain, Switzerland, Italy, Lithuania, Lithonia, Estonia), South America (Chile), Australia, New Zealand.

 

Introduction reasons

Probably for ornamental purposes. Used as an ornamental plant in fishkeeping.

 

Preferential invasion environments

Lagoons, ditches and rice fields.

It grows between 0,5 and 7 cm deep, standing still or moving slowly.

It develops mainly in basic, cold and limpid water.

 

Although it’s considered as being an invasive species, its dispersion in Portugal is relatively limited.

Impacts on ecossystems

It grows into mats that may totally cover the water surface. Its growth reduces the water flow up to 80%, changes the available lighting and prevents the growth of native species.

 

Economic impacts

It diminishes the recreational use of the invaded area and may cause problems in irrigation systems.

Potentially high costs in applying control measures.

 

Natura 2000 network habitats more subject to impacts

– Natural euthrophic lakes with Magnopotamion or Hydrocharition-type vegetation (3150).

 

Controlling an invasive species demands a well-planned management, which includes the determination of the invaded area, identifying the causes of invasion, assessing the impacts, defining the intervention priorities, selecting the adequate control methodologies and their application. Afterwards it is fundamental to monitor the efficiency of the methodologies and recuperation of the intervened area as to perform, whenever necessary, the follow-up control.

The control methodologies used for Elodea canadensis include:

 

Physical control

Manual/mechanical removal (preferential methodology). Manual removal or by using nets and dredging. For the success of this methodology, it’s fundamental not to create and/or leave large fragments in the water.

Shadowing of the invaded waterbodies. The shadowing may be obtained by tree planting on the banks of the affected areas or by applying an opaque covering.

 

Chemical control

Herbicide application. Herbicide spray (active substance: diquat in formulas adapted to aquatic environments). It is expensive and only temporary. It affects non-target species and its efficiency is very dependent on the age and phenological state of the plants and the presence of debris in the water, so it may result in very low success rates.

 

Biological control

The presence of carps and other fishes enhances the water’s turbidity and, thus, reduces the probability of the species’ expansion.

 

Visit the webpage How to Control for additional and more detailed information about the correct application of these methodologies.

 

CABI (2012) Elodea canadensis. In: Invasive Species Compendium. CAB International, Wallingford, UK. Available: http://www.cabi.org/isc/ [Retrieved 29/11/2012].

DAISIE European Invasive Alien Species Gateway (2012) Elodea canadensis. Available: http://www.europe-aliens.org/speciesFactsheet.do?speciesId=1052 [Retrieved 29/11/2012].

DiTomaso JM, Healy EA (2003) Aquatic and riparian weed of the West. University of California; Agriculture and Natural Resources. Oakland.California 442pp.

Global Invasive Species Database (2012) Elodea canadensis. Available: http://www.issg.org/database/species/search.asp?sts=sss&st=sss&fr=1&x=0&y=0&sn=elodea+canadensis&rn=&hci=-1&ei=-1&lang=EN [Retrieved 29/11/2012].

Marchante E, Freitas H, Marchante H (2008) Guia prático para a identificação de plantas invasoras de Portugal Continental. Imprensa da Universidade de Coimbra, Coimbra, 183pp.

Vernon E, Hamilton H (2011) Literature review on methods of control and eradication of Canadian pondweed and Nuttall’s pondweed in standing waters. Scottish Natural Heritage Commissioned Report n° 433, 45pp.

 

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