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Myriophyllum aquaticum

Aquatic herb, similar to a small pine tree, with emergent bluish-green leaves.

Scientific name: Myriophyllum aquaticum (Velloso) Verdc.

Common names: parrotfeather, Brazilian watermilfoil

Family: Haloragaceae

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: Myriophyllum brasiliense Cambess, Myriophyllum aquaticum (Vell.) Verdc., Enydria aquatica Vell., Myriophyllum proserpinacoides Gillies ex Hook. & Arn.

Last update: 08/07/2014

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How to recognise it

Aquatic herb up to 2 m, sometimes sub-woody on the base.

Leaves: 4-6 leaves per node, with 15-40 mm, normally longer (the emerging ones) than the ones from the internodes; emergent bluish-green leaves, covered by hemispherical glands, tiny and transparent, and cut-out in 8-30 segments of 3-6 mm.

Flowers: unisexual, willowish or light pink, solitary, axillary; male flowers petals with 5 mm, inexistent in the female ones.

Fruits: ovoid, papillose, with 1,8 X 1,2 mm.

Flowering: May to October.

 

Similar species

Myriophyllum verticillatum L. is relatively similar, but the leaves generally have more segments (24-35), the flowers are verticillate and the petals of male flower are only 2,5 mm long.

 

Characteristics that aid invasion

Outside the native distribution area, it only propagates vegetatively by stem fragmentation. It doesn’t form self-fragments, but these are formed by mechanical actions, rooting rapidly.

The rhizomes are resistant, travelling long distances clutching on to the bottom of vessels. The aerial parts grow both out of the water and submersed.

 

Native distribution area

South America: southern states of Brazil, Peru, Uruguay, Argentina and Chile.

 

Distribution in Portugal

Mainland Portugal (Minho, Douro Litoral, Beira Litoral, Estremadura, Ribatejo, Alto Alentejo).

Geographic areas where there are records of Myriophyllum aquaticum

Other places where the species is invasive

Parts of Europe, Australia, South Africa, New Zealand, North America, Japan, Indonesia.

 

Introduction reasons

For ornamental purposes, although there’s some controversy about possible accidental introduction. Used as an ornamental plant in fishkeeping.

 

Preferential invasion environments

Lagoons, ditches, water bodies, swamps and soggy soils.

 

 

Impacts on ecossystems

It forms mats that may totally cover the water surface. Its growth reduces the quality of the water, biodiversity, available light and water flow.

 

Economic impacts

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

High costs in applying control measures.

 

Other impacts

It increases the incidence of mosquitos.

 

Natura 2000 network habitats more subject to impacts

– Hard oligo-mesotrophic waters with benthic vegetation of Chara spp. (3140);
– Natural euthrophic lakes with Magnopotamion or Hydrocharition-type vegetation(3150);
– Natural dystrophic lakes and ponds (3160);
– Constantly flowing Mediterranean rivers with Paspalo-Agrostidion species and hanging curtains of Salix and Populus alba (3280).

 

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 Myriophyllum aquaticum 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 water bodies. The shadowing may be obtained by tree planting on the banks of the affected areas or by applying an opaque covering.

 

Chemical control

Foliar application of herbicide. Herbicide spray (active substance: 2,4-D in formulas adapted to aquatic environments) limiting the application to the target species.

 

Biological control

The flea beetle Lysathia sp. (Coleoptera: Chrysolmelidae), was introduced in South Africa in 1994, causing nowadays extensive damage to Myriophyllum aquaticum.

This agent has not yet been tested in Portugal as to verify its safety relatively to native species, so its use has not yet constituted an alternative in our country.

 

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

Agricultural Research Council – Plant Protection Research Institute – Weed Research Division (2014) Management of invasive alien plants: A list of biocontrol agents released against invasive alien plants in South Africa. Available: http://www.arc.agric.za/arc-ppri/Documents/WebAgentsreleased.pdf  [Retrieved 03/03/2014].

CABI (2012) Myriophyllum aquaticum. In: Invasive Species Compendium. CAB International, Wallingford, UK. Available: http://www.cabi.org/isc/ [Retrieved 10/11/2012].

Cilliers CJ (1999) Biological control of parrot’s feather, Myriophyllum aquaticum (Vell.) Verdc. (Haloragaceae), in South Africa. African Entomology Memoir no1: 113-118.

Dufour-Dror J-M (2012) Alien invasive plants in Israel. The Middle East Nature Conservation Promotion Association, Ahva, Jerusalem,213pp.

Global Invasive Species Database (2012) Myriophyllum aquaticum. Available: http://www.issg.org/database/species/ecology.asp?si=70&fr=1&sts=sss [Retrieved 12/11/2012].

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.

Moreira I, Monteiro A, Ferreira T (1999) Biology and controlo of parrotfeather (Myriophyllum aquaticum) in Portugal. Ecology, Environment and Conservation 5(3): 171-179.

Teles NA, Pinto da Silva AR (1975) A “pinheirinha” (Myriophyllum aquaticum (Vell.) Verdc.), uma agressiva infestante aquática. Agronomia lusitana, 36(3): 307-323.

USDA, NRCS. (2012) The PLANTS Database. National Plant Data Team, Greensboro, NC 27401-4901 USA.  Available: http://plants.usda.gov [Retrieved 12/11/2012].

Washington State Department of Ecology (2012) Technical information about Parrotfeather (Myriophyllum aquaticum). Available: http://www.ecy.wa.gov/programs/wq/plants/weeds/aqua003.html [Retrieved 12/11/2012].

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