Risk analysis of the Variable Watermilfoil Myriophyllum heterophyllum Michaux. - Risk analysis report of non-native organisms in Belgium from the Royal Belgian Institute of Natural Sciences for the Federal Public Service Health, Food chain safety and Environment.

Abstract

PROBABILITY OF ESTABLISHMENT AND SPREAD (EXPOSURE)

Entry in Belgium

The species was first recorded in the wild in Belgium in 1993 and is now established at a few
sites (principally in Campine). The main pathway of entry is the trade for ornamental use in
ponds and in aquaria with subsequent disposal of cultivated plants into the wild and possibly
further natural spread.

Establishment capacity

M. heterophyllum occurs as an aquatic plant in lakes, ponds and wetlands and can also grow
in a semi-terrestrial form. The required climatic and environmental characteristics occur in
Belgium and sensitive areas, nature reserves and Natura2000 sites are vulnerable to
invasion. The currently limited distribution in Belgium might result from the presence of a
natural control agent, the aquatic weevil Eubrychius velutus , the specific genetic lineages
that are present or competitive plants, present here and not in north-eastern USA, or by a
combination of these factors.

Dispersion capacity

The capacity of the species to colonize new areas is clearly linked to human-mediated
dispersion, mainly through trade and subsequent disposal of aquaria contents into local
waterways and ponds. In non-native areas, where the species shows invasive characters,
short distance dispersal through vegetative fragments is facilitated by animal vectors and
human activities (transport on human clothing, footwear, machinery, boats or fishing
equipment, weed cutting,..).

EFFECT OF ESTABLISHMENT

Environmental impacts

Where the species is invasive, observed environmental impacts include habitat alteration,
modification of natural benthic communities, modification of nutrient regimes, and
modification of succession patterns. All those impacts can conduct locally to a reduction of
native biodiversity, threat to and loss of endangered species. Some infrastructure damage
and damage to ecosystem services have also been mentioned.

None of these impacts have been observed on a large scale in Belgium or in Europe yet but it
could happen if the species became an aggressive invasive.

RISK MANAGEMENT

As with most of the other Invasive Alien Species, the best way to deal with the threat posed
by Myriophyllum heterophyllum to biodiversity and society is through a combination of preventive measures, early detection and rapid response to new incursions, with permanent
management only as the last option.

It is particularly important for this species, which is not yet invasive in Europe, to prevent
additional introductions of more aggressive genetic lineages, in particular potential hybrids.
It is advised to amend and/or reinforce regulations in order to ban completely this species
from import, personal holding and commercial trades.

Full text

Risk analysis report of non-native organisms
in Belgium
Risk analysis of the Variable Watermilfoil
Myriophyllum heterophyllum Michaux
René-Marie Lafontaine – Roseline C. Beudels-Jamar – Thibaut
Delsinne – Henri Robert
Royal Belgian Institute of Natural Sciences ; OD Natural Environment ; Conservation Biology Team ; Rue Vautier
29, 1000 Brussels ; http://www.sciencesnaturelles.be
Reviewed by :
Luc Denys (INBO)
Mathieu Halford (Université de Liège – Gembloux Agro-Bio Tech.)
Arnaud Monty (Université de Liège – Gembloux Agro-Bio Tech.)
Floris Vanderhaeghe (INBO)
Adopted in date of:
11th March 2013
Commissioned by:
Federal Public Service Health, Food chain safety and Environment
Contact person:
Rene-Marie.Lafontaine@naturalsciences.be
This report should be cited as:
Lafontaine, R.-M., Beudels-Jamar, R.C., Delsinne, T., Robert, H. (2013). Risk analysis of the Variable
Watermilfoil Myriophyllum heterophyllum Michaux. - Risk analysis report of non-native organisms in
Belgium from the Royal Belgian Institute of Natural Sciences for the Federal Public Service Health,
Food chain safety and Environment. 33 p.

Page 1
Contents
Acknowledgements ............................................................................................................................... 2
Rationale and scope of the Belgian risk analysis scheme ...................................................................... 3
Executive summary ................................................................................................................................ 5
Résumé .................................................................................................................................................. 7
Samenvatting ......................................................................................................................................... 9
STAGE 1: INITIATION .................................................................................................................... 11
1.1 ORGANISM IDENTITY ..................................................................................................................... 11
1.2 SHORT DESCRIPTION ...................................................................................................................... 11
1.3 ORGANISM DISTRIBUTION ............................................................................................................. 12
1.4 REASONS FOR PERFORMING RISK ANALYSIS ................................................................................. 14
STAGE 2 : RISK ASSESSMENT ........................................................................................................ 15
2.1 PROBABILITY OF ESTABLISHMENT AND SPREAD (EXPOSURE) ....................................................... 15
2.1.1 Present status in Belgium ............................................................................................... 15
2.1.2 Present status in neighbouring countries ...................................................................... 17
2.1.3 Introduction in Belgium ................................................................................................. 19
2.1.4 Establishment capacity and endangered area ............................................................... 19
2.1.5 Dispersion capacity ........................................................................................................ 23
2.2 EFFECTS OF ESTABLISHMENT ......................................................................................................... 24
2.2.1 Environmental impacts .................................................................................................. 24
2.2.2 Other impacts ................................................................................................................ 26
STAGE 3 : RISK MANAGEMENT ..................................................................................................... 27
3.1 RELATIVE IMPORTANCE OF PATHWAYS FOR INVASIVE SPECIES ENTRY IN BELGIUM .................... 27
3.2 PREVENTIVE ACTIONS .................................................................................................................... 27
3.3 CONTROL AND ERADICATION ACTIONS ......................................................................................... 28
LIST OF REFERENCES ............................................................................................................................ 31

Page 2
Acknowledgements
The authors wish to thank the reviewers who contributed to this risk analysis with valuable
comments and additional references: Luc Denys (INBO), Mathieu Halford (Université de Liège
– Gembloux Agro-Bio Tech.), Arnaud Monty (Université de Liège – Gembloux Agro-Bio Tech.)
and Floris Vanderhaeghe (INBO). They also thank Isabelle Bachy (RBINS) who designed the
PRA’s cover.
Etienne Branquart (Cellule Espèces Invasives, Service Public de Wallonie) developed the risk
analysis template that was used for this exercise.
The general process of drafting, reviewing and approval of the risk analysis for selected
invasive alien species in Belgium was attended by a steering committee, chaired by the
Federal Public Service Health, Food chain safety and Environment. RBINS/KBIN was
contracted by the Federal Public Service Health, Food chain safety and Environment to
perform PRA’s for a batch of species. ULg was contracted by Service Public de Wallonie to
perform PRA’s for a selection of species. INBO and DEMNA performed risk analysis for a
number of species as in-kind contribution.
Steering committee members were:
Tim Adriaens Research Institute for Nature and Forest (INBO)
Olivier Beck Brussels Environment (BIM)
Roseline Beudels-Jamar Royal Belgian Institute of Natural Sciences (RBINS/KBIN)
Etienne Branquart Département de l’Etude du Milieu Naturel et Agricole (DEMNA)
Jim Casaer Research Institute for Nature and Forest (INBO)
Thibaut Delsinne Royal Belgian Institute of Natural Sciences (RBINS/KBIN)
Maud Istasse (chair) Federal Public Service Health, Food chain safety and Environment
René-Marie Lafontaine Royal Belgian Institute of Natural Sciences (RBINS/KBIN)
Alice Lejeune Federal Public Service Health, Food chain safety and Environment
Céline Prévot Département de l’Etude du Milieu Naturel et Agricole (DEMNA)
Henri Robert Royal Belgian Institute of Natural Sciences (RBINS/KBIN)
Vinciane Schockert Université de Liège (ULg)
Sonia Vanderhoeven Belgian Biodiversity Platform (BBPF)
Hans Van Gossum Agency for Nature and Forest (ANB)
Hugo Verreycken Research Institute for Nature and Forest (INBO)

Page 3
Rationale and scope of the Belgian risk analysis scheme
The Convention on Biological Diversity (CBD) emphasises the need for a precautionary
approach towards non-native species. It strongly promotes the use of robust and good
quality risk assessment to help underpin this approach (COP 6 Decision VI/23). More
specifically, when considering trade restrictions for reducing the risk of introduction and
spread of a non-native organisms, full and comprehensive risk assessment is required to
demonstrate that the proposed measures are adequate and efficient to reduce the risk and
that they do not create any disguised barriers to trade. This should be seen in the context of
WTO and free trade as a principle in the EU (Baker et al. 2008, Shine et al. 2010, Shrader et
al. 2010).
This risk analysis has the specific aim of evaluating whether or not to install trade restrictions
for a selection of absent or emerging invasive alien species that may threaten biodiversity in
Belgium as a preventive risk management option. It is conducted at the scale of Belgium but
results and conclusions could also be relevant for neighbouring areas with similar eco-
climatic conditions (e.g. areas included within the Atlantic and the continental biogeographic
regions in Europe).
The risk analysis tool that was used here follows a simplified scheme elaborated on the basis
of the recommendations provided by the international standard for pest risk analysis for
organisms of quarantine concern
1
produced by the secretariat of the International Plant
Protection Convention (FAO 2004). This logical scheme adopted in the plant health domain
separates the assessment of entry, establishment, spread and impacts. As proposed in the GB
non-native species risk assessment scheme, this IPPC standard can be adapted to assess the
risk of intentional introductions of non-native species regardless the taxon that may or not be
considered as detrimental (Andersen 2004, Baker et al. 2005, Baker et al. 2008, Schrader et
al. 2010).
The risk analysis follows a process defined by three stages : (1) the initiation process which
involves identifying the organism and its introduction pathways that should be considered for
risk analysis in relation to Belgium, (2) the risk assessment stage which includes the
categorization of emerging non-native species to determine whether the criteria for a
quarantine organism are satisfied and an evaluation of the probability of organism entry,
establishment, spread, and of their potential environmental, economic and social
consequences and (3) the risk management stage which involves identifying management
options for reducing the risks identified at stage 2 to an acceptable level. These are evaluated
for efficacy, feasibility and impact in order to select the most appropriate. The risk
management section in the current risk analysis should however not been regarded as a full-
option management plan, which would require an extra feasibility study including legal,
technical and financial considerations. Such thorough study is out of the scope of the
produced documents, in which the management is largely limited to identifying needed
1
1
A weed or a pest organism not yet present in the area under assessment, or present but not
widely distributed, that is likely to cause economic damages and is proposed for official regulation and
control (FAO 2010).

Page 4
actions separate from trade restrictions and, where possible, to comment on cost-benefit
information if easily available in the literature.
This risk analysis is an advisory document and should be used to help support Belgian
decision making. It does not in itself determine government policy, nor does it have any legal
status. Neither should it reflect stakeholder consensus. Although the document at hand is of
public nature, it is important to realise that this risk assessments exercise is carried out by
(an) independent expert(s) who produces knowledge-based risk assignments sensu Aven
(2011). It was completed using a uniform template to ensure that the full range of issues
recognised in international standards was addressed.
To address a number of common misconceptions about non-native species risk assessments,
the following points should be noted (after Baker et al. 2008):
2 Risk assessments are advisory and therefore part of the suite of information on which
policy decisions are based;
3 The risk assessment deals with potential negative (ecological, economic, social)
impacts. It is not meant to consider positive impacts associated with the introduction
or presence of a species, nor is the purpose of this assessment to perform a cost-
benefit analysis in that respect. The latter elements though would be elements of
consideration for any policy decision;
4 Completed risk assessments are not final and absolute. New scientific evidence may
prompt a re-evaluation of the risks and/or a change of policy.
Myriophyllum heterophyllum (Photo : Andreas Hussner).

Page 5
Executive summary
PROBABILITY OF ESTABLISHMENT AND SPREAD (EXPOSURE)
Entry in Belgium
The species was first recorded in the wild in Belgium in 1993 and is now established at a few
sites (principally in Campine). The main pathway of entry is the trade for ornamental use in
ponds and in aquaria with subsequent disposal of cultivated plants into the wild and possibly
further natural spread.
Establishment capacity
M. heterophyllum occurs as an aquatic plant in lakes, ponds and wetlands and can also grow
in a semi-terrestrial form. The required climatic and environmental characteristics occur in
Belgium and sensitive areas, nature reserves and Natura2000 sites are vulnerable to
invasion. The currently limited distribution in Belgium might result from the presence of a
natural control agent, the aquatic weevil Eubrychius velutus , the specific genetic lineages
that are present or competitive plants, present here and not in north-eastern USA, or by a
combination of these factors.
Dispersion capacity
The capacity of the species to colonize new areas is clearly linked to human-mediated
dispersion, mainly through trade and subsequent disposal of aquaria contents into local
waterways and ponds. In non-native areas, where the species shows invasive characters,
short distance dispersal through vegetative fragments is facilitated by animal vectors and
human activities (transport on human clothing, footwear, machinery, boats or fishing
equipment, weed cutting,..).
EFFECT OF ESTABLISHMENT
Environmental impacts
Where the species is invasive, observed environmental impacts include habitat alteration,
modification of natural benthic communities, modification of nutrient regimes, and
modification of succession patterns. All those impacts can conduct locally to a reduction of
native biodiversity, threat to and loss of endangered species. Some infrastructure damage
and damage to ecosystem services have also been mentioned.
None of these impacts have been observed on a large scale in Belgium or in Europe yet but it
could happen if the species became an aggressive invasive.
RISK MANAGEMENT
As with most of the other Invasive Alien Species, the best way to deal with the threat posed
by Myriophyllum heterophyllum to biodiversity and society is through a combination of

Page 6
preventive measures, early detection and rapid response to new incursions, with permanent
management only as the last option.
It is particularly important for this species, which is not yet invasive in Europe, to prevent
additional introductions of more aggressive genetic lineages, in particular potential hybrids.
It is advised to amend and/or reinforce regulations in order to ban completely this species
from import, personal holding and commercial trades.

Page 7
Résumé
PROBABILITE D’ETABLISSEMENT ET DE DISSEMINATION (EXPOSITION)
Introduction en Belgique
Myriophyllum heterophyllum a été enregistrée en milieu naturel en Belgique pour la
première fois en 1993 ; elle est aujourd’hui établie dans plusieurs sites (en Campine
essentiellement). La principale voie d’introduction de cette espèce dans notre
environnement est le commerce horticole et sa vente comme plante ornementale pour les
étangs et les aquariums.
Capacité d’établissement
M. heterophyllum est une plante aquatique qui se développe dans les lacs, les étangs et les
zones humides mais aussi en milieu semi-terrestre. Les caractéristiques climatiques et
environnementales nécessaires à sa prolifération sont réunies en Belgique et de nombreuses
zones sensibles, réserves naturelles et sites Natura 2000 peuvent potentiellement être
envahis par l’espèce. Sa distribution actuellement encore limitée en Belgique pourrait être
due à la présence d’un agent de contrôle naturel comme le charançon aquatique Eubrychius
velutus, à l’absence d’une lignée génétique agressive ou à la présence d’autres espèces de
plantes compétitives voire à une combinaison de ces divers facteurs.
Capacité de dispersion
La capacité de l’espèce à coloniser de nouveaux habitats est clairement favorisée par les
actions humaines, principalement par le biais du commerce et de l’élimination du contenu
des aquariums dans les cours d'eau locaux et les étangs. Dans les zones exotiques où l'espèce
présente un caractère envahissant, la dispersion à courte distance de fragments végétatifs de
M. heterophyllum est facilitée par les animaux et les activités humaines (transport sur les
vêtements, chaussures, outils, machines, bateaux, équipement de pêche et suite à des
activités de désherbage/traitement de zones infestées).
EFFET DE L’ETABLISSEMENT
Impacts environnementaux
Dans les habitats où l'espèce est envahissante, les impacts environnementaux observés
comprennent une altération de l’habitat, une modification des communautés naturelles
benthiques, une modification de la disponibilité en éléments nutritifs et une perturbation
des patrons de succession écologique. Tous ces impacts peuvent mener, localement, à une
réduction de la biodiversité indigène et à une menace supplémentaire sur les espèces déjà
vulnérables voire leur disparition. Des dommages aux infrastructures ainsi qu’aux services
écosystémiques ont déjà été mentionnés.
Aucun de ces impacts n’a encore été observé à grande échelle en Belgique ou en Europe
pour l’instant mais ce pourrait être le cas si l’espèce devenait une espèce fortement
envahissante.

Page 8
GESTION DES RISQUES
Comme pour la majorité des autres espèces exotiques envahissantes, le meilleur moyen de
traiter la menace que représente Myriophyllum heterophyllum pour la biodiversité et la
société est de combiner différentes mesures de prévention, d’assurer la détection précoce et
une réponse rapide aux nouveaux envahissements et de ne considérer la gestion que comme
l’option de dernier recours.
Il est particulièrement important pour cette espèce (qui n'a pas encore de caractère
envahissant en Europe) d'empêcher toute introduction de lignée génétique agressive de
l’espèce (certaines souches hybrides en particulier). Il est par conséquent conseillé de
modifier et/ou de renforcer les réglementations afin d’interdire complètement l’importation,
la détention à titre individuel et le commerce de cette espèce.

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Samenvatting
WAARSCHIJNLIJKHEID VAN VESTIGING EN VERSPREIDING (BLOOTSTELLING)
Introductie in België
Myriophyllum heterophyllum werd in België voor het eerst waargenomen in 1993 en is nu in
een beperkt aantal gebieden gevestigd. De voornaamste introductieweg is de handel in
sierplanten voor vijvers en aquaria en daar op volgend het wegwerpen of uitplanten van
gekweekte planten in het wild.
Vestigingsvermogen
M. heterophyllum is een waterplant van meren, vijvers en waterlopen. Ze kan ook in een
semi-terrestrische vorm groeien. De vereiste klimaat- en omgevingseigenschappen zijn in
België aanwezig; kwetsbare gebieden, natuurgebieden en Natura2000 gebieden zijn
kwetsbaar voor invasie. De momenteel nog beperkte verspreiding in België kan een gevolg
zijn van de aanwezigheid van natuurlijke controleagentia, zoals de in het water levende
snuitkever Eubrychius velutus, het genetisch profiel van de aanwezige planten, of
concurrerende plantensoorten die niet in het noordoosten van de VS voorkomen, of een
combinatie van deze factoren.
Verspreidingsvermogen
Het vermogen van de soort om nieuwe gebieden te koloniseren hangt duidelijk samen met
de verspreiding door de mens, overwegend via handel en het vervolgens werwerpen of
uitplanten van aquariumplanten in waterlopen en vijvers. In gebieden waar de soort niet-
inheems is en een invasief karakter vertoont, wordt de verspreiding over korte afstand door
vegetatieve fragmenten in de hand gewerkt door dierlijke vectoren en menselijke
activiteiten (transport op kledij en schoeisel, met machines, boten of visgerei, maaien van
waterplanten, ...).
EFFECTEN VAN DE VESTIGING
Milieu-impact
Waar de soort omvangrijke en dichte bestanden vormt kan dit leiden tot wijziging van de
milieuomstandigheden (ondermeer nutriënten- en zuurstofregime), de levensgemeenschap
en het voedselweb. Hierdoor kan de inheemse biodiversiteit plaatselijk afnemen met verlies
van bedreigde soorten. Ook is schade aan infrastructuur en aan ecosysteemdiensten
gemeld.
Dergelijke negatieve gevolgen zijn nog niet in België vastgesteld, maar kunnen optreden bij
verdere verspreiding en ontwikkeling van grote populaties. In Nederland zorgt de soort
reeds voor overlast.

Page 10
RISICOBEHEER
Een combinatie van preventieve maatregelen, vroege opsporing en snelle reactie op initiële
vestiging biedt de beste bescherming. Mechanische bestrijding is mogelijk maar mag
vegetatieve verspreiding middels fragmenten niet in de hand werken. Voldoende nazorg is
steeds noodzakelijk.
Eventuele bijkomende introductie van meer invasieve genetische lijnen, en hybriden dient te
worden voorkomen. Het beperken of volledig verbieden van invoer, het persoonlijk bezit en
de verkoop wordt daarom aangeraden.

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STAGE 1: INITIATION
Present its distribution and pathways of quarantine concern that should be considered for risk analysis in Belgium.
A short morphological description can be added if relevant. Specify also the reason(s) why a risk analysis is needed
(the emergency of a new invasive organism in Belgium and neighboring areas, the reporting of higher damages
caused by a non- native organism in Belgium than in its area of origin, or request made to import a new non-
native organism in the Belgium).
1.1 ORGANISM IDENTITY
Scientific name : Myriophyllum heterophyllum, Michaux 1803
Synonyms: Myriophyllum elatinoides Gaudichaud-Beaupré 1825, Potamogeton
verticillatum Walter.
Common names : Broadleaf Watermilfoil (Eng), Twoleaf Watermilfoil (US), Variable
Watermilfoil (Eng); Myriophylle hétérophylle (FR); Ongelijkbladig
vederkruid (Nl); Verschiedenblättriges Tausendblatt (Ge)
Taxonomic position: Magnoliophyta » Magnoliophyta » Rosopsida » Saxifragales »
Haloragaceae »
Myriophyllum heterophyllum
1.2 SHORT DESCRIPTION
M. heterophyllum is an aquatic plant that has submerged vegetation with emergent
flowering spikes. It is a perennial, aquatic herb that has leaves of two noticeably different
forms. The submerged leaves are finely dissected, whorled, reddish/greenish-brown, and 1.3-
6.4 cm long. The emergent leaves are small, oval, bright green, whorled and up to 0.6 cm
wide. Emergent leaves stand 15.2-20.3 cm out of the water and may not be apparent until
late summer. Flowering occurs from June to September. Flowers are emergent on 5.1-30.5
cm, green to reddish stalks. Petals are less than 3 mm in length and are subtended by
downward curved bracts. Fruits are small, nearly round and have a rough surface
(summarized from Aiken, 1981).
A very similar Australian species (likewise with conspicuous floral bracts) is also cultivated as
an ornamental in Europe, Myriophyllum simulans (see Jäger et al. 2008). It is best
distinguished in having 8 stamens, not 4. It is not impossible that these two species are
intermixed.

Page 12
Figure 1. Submerged and emergent leaves of M. heterophyllum
(http://www.invasive.org/browse/detail.cfm?imgnum=5308025).
1.3 ORGANISM DISTRIBUTION
Native range
The native distribution of M. heterophyllum is known in general, but not documented in
detail. Aiken (1981) lists its distribution in North America as ‘Virginia to Florida, northward to
Ontario and Michigan, and westward to Missouri and Texas’.
There is no consensus on the native distribution of this species, for example USDA (United
States Department of Agriculture) considers the species indigenous in Eastern North America
(Canada and USA), and exotic in Western North America. But the species is usually
considered as native to the eastern part of the USA, except the north-eastern region. More
precisely it is considered non-native and invasive in New England, where it appears to have
been introduced circa 1932 by escape from cultivation with subsequent spread via vegetative
propagules (Les & Mehrhoff, 1999). Since its initial introduction to New England, it has
spread throughout the region and is the most common invasive aquatic plant in New
Hampshire (Thum & Lennon, 2009). It is not clear if M. heterophyllum was historically native
to the mid-Atlantic region (Delaware, Maryland, New Jersey, New York, Pennsylvania and
Virginia). For example, it is treated as a non-native invasive species in New York and eastern
Pennsylvania, but is considered an extremely rare native and threatened species in nearby
Delaware. Part of the confusion regarding its historical status (native/non-native) in north-
eastern USA may result from confusion with the closely related species M. pinnatum, which

Page 13
is considered native along the eastern coast from Florida through eastern Massachusetts
(Aiken, 1981).
M. heterophyllum is definitively considered as non-native in western USA: while it is not clear
when it was first introduced there, its recent spread in the region - especially in Washington
state - is causing concern among water resource managers. Two causes for concern include
the possible misidentification of M. heterophyllum with the closely-related, morphologically
similar, and endemic western watermilfoil, M. hippuroides, and the potential for
hybridization between the two species.
Introduced range
Belgium:
A rare, locally naturalised alien, probably overlooked. First recorded in a dead branch of river
Meuse near Lives-sur-Meuse in 1993 (along with Lagarosiphon major; see Bouxin &
Lambinon 1996) but soon disappeared from the site. Recently discovered in several canals
and other artificial water courses (chiefly in Antitank-ditch, Dessel-Schoten canal) in the
northern parts of Antwerpen province (De Beer & De Vlaeminck 2008). The species was
probably already present there for considerable time, possibly even since the late seventies
but it was thought to be M. spicatum at the time (Luc Denys pers. com.).
Rest of Europe:
Myriophyllum heterophyllum has been recorded in Austria, France (not established yet, first
found in 2011), Germany, Netherlands and Spain, ( + Switzerland and Great Britain fide EPPO
2011, not confirmed).

Page 14
Figure 2. European countries where Myriophyllum heterophyllum occurs
The exact origin of European populations of Myriophyllum heterophyllum is rather obscure. It
is known since the 1940’s from Germany (Wimmer 1997, Hussner et al. 2005). Wann (1997)
does not mention it as an ornamental in European gardens (see however Jäger et al. 2008). It
was most likely introduced as an aquarium plant and managed to escape (from discarded
aquarium contents).
Other continents:
M. heterophyllum was also introduced and is now recorded in China (Yu et al. 2003).
1.4 REASONS FOR PERFORMING RISK ANALYSIS
M. heterophyllum is highly competitive and can grow and spread rapidly, and is able to
displace other submerged macrophyte species. It produces dense mats that reduce sunlight
and can restrict water movement., These can results in a reduction of water quality and of
available oxygen, particularly when decomposing. The low oxygen conditions can kill fish and
harm other aquatic organisms. The dense mats can impede swimming, boating and fishing.
Moreover in north-eastern USA dense mats along lake shorelines have been reported to
reduce property values by 20-40% (EPPO, 2012). In eastern USA, the species hybridizes with
the native M. laxum, resulting in a more aggressive hybrid Myriophyllum heterophyllum x
laxum (Moody & Les, 2002).

Page 15
Myriophyllum heterophyllum is an aquatic perennial plant native to the Southeast of the
USA. The species is used in fish tanks and for ornamental purposes in ponds. Within Europe,
including Belgium, its distribution is still limited. Because this plant has shown invasive
behaviour where it was introduced (elsewhere in North America) it was included in the EPPO
List of Invasive Alien Plants in 2012. Because its presence is still limited in Europe, this species
can be considered as an emerging invader in Europe.

Page 16
STAGE 2 : RISK ASSESSMENT
2.1 PROBABILITY OF ESTABLISHMENT AND SPREAD (EXPOSURE)
Evidence should be available to support the conclusion that the non-native organism could enter, become
established in the wild and spread in Belgium and neighbouring areas. An analysis of each associated pathways
from its origin to its establishment in Belgium is required. Organisms intentionally imported maybe maintained in
a number of intended sites for an indeterminate period. In this specific case, the risk may arise because of the
probability to spread and establish in unintended habitats nearby intended introduction sites.
2.1.1 Present status in Belgium
Specify if the species already occurs in Belgium and if it makes self-sustaining populations in the wild
(establishment). Give detail about species abundance and distribution within Belgium when establishment is
confirmed together with the size of area suitable for further spread within Belgium.
A rare, locally naturalised alien, possibly overlooked. First recorded in a dead branch of river
Meuse near Lives-sur-Meuse in 1993 (along with Lagarosiphon major; see Bouxin &
Lambinon 1996) but soon gone. Recently discovered again in several canals and other
artificial water courses (chiefly in antitank-ditches, Dessel-Schoten kanaal) in the northern
parts of Antwerpen province (De Beer & De Vlaeminck 2008). Most records were made from
2007 onwards, but the dimensions of some populations suggest a much longer presence.
One herbarium collection (Antitank ditch near Sint-Job-in-‘t-Goor) dates back to 1999.
Myriophyllum heterophyllum appears to be firmly established in several localities but does
not (yet) seem to spread in an invasive way.
Established populations
absent from district
isolated populations (1-5 localities per district)
widespread (>5 localities per district)
Figure 3. Established population of Myriophyllum heterophyllum by geographic district in
Belgium. Source: http://ias.biodiversity.be

Page 17
The species has also been recently recorded (30/12/2011) in one pond near Brûly-de-Pesche
(Namur province) (fide Observations.be; not recorded in DEMNA database 2013).
2.1.2 Present status in neighbouring countries
Netherlands
Recently found (first recorded in 2001) in stagnant or slowly flowing, eutrophic or
less eutrophic water systems (Luijten & Odé, 2007). Due to confusion with M.
aquaticum by observers records are not always correctly reported and the map is
possibly incomplete.
Figure 4.Distribution of Myriophyllum heterophyllum in the Netherlands (http://www.q-
bank.eu).

Page 18
France
Myriophyllum heterophyllum is not yet firmly established in France, but it was found for the
first time in 2011, in a small pond in Saint-Sylvestre (Haute-Vienne) (ANSES, 2011).
Germany
Variable Watermilfoil is a naturalized neophyte in Germany. First recorded during the 1940’s
and considered established since the end of the 1950’s (FloraWeb, 2009). Its present
distribution and abundance seem not well documented but it is established in at least 6
Länder.
Figure 5. Distribution of Myriophyllum heterophyllum in Germany, Dark green = Länder
where the species is established (etabliert)
2
.
2

Page 19
United Kingdom
Myriophyllum heterophyllum has not yet been recorded in the UK (NBN gateway, 2013).
2.1.3 Introduction in Belgium
Specify what are the potential international introduction pathways mediated by human, the frequency of
introduction and the number of individuals that are likely to be released in Europe and in Belgium. Consider
potential for natural colonisation from neighbouring areas where the species is established and compare with the
risk of introduction by the human-mediated pathways. In case of plant or animal species kept in captivity, assess
risk for organism escape to the wild (unintended habitats).
Myriophyllum heterophyllum appears to be established in several localities in Europe and a
few sites in Belgium but does not (yet) seem to spread in an invasive way. It is considered
most likely that all occurrences in the wild derive from plants discarded when clearing out
ponds.
Human-mediated pathways is the main risk of introduction. In fact, the only pathway
mentioned for long distance dispersal of Myriophyllum heterophyllum in scientific literature
is horticultural and aquarium trade. The species is widely sold as an aquarium and garden
pond plant.
ENTRY IN BELGIUM
Aquarium and horticultural trade is the only introduction pathway identified. In its initial
Belgian (in 1983) and European (in 1940’s) localities it was most likely introduced as an
ornamental plant and later managed to escape from discarded aquarium or garden debris.
2.1.4 Establishment capacity and endangered area
Provide a short description of life-history and reproduction traits of the organism that should be compared with
those of their closest native relatives (A). Specify which are the optimal and limiting climatic (B), habitat (C) and
food (D) requirements for organism survival, growth and reproduction both in its native and introduced ranges.
When present in Belgium, specify agents (predators, parasites, diseases, etc.) that are likely to control population
development (E). For species absent from Belgium, identify the probability for future establishment (F) and the
area most suitable for species establishment (endangered area) (G) depending if climatic, habitat and food
conditions found in Belgium are considered as optimal, suboptimal or inadequate for the establishment of a

http://www.aquatischeneophyten.de/Bilder/Verbreitungskarten%20deutsche%20Version/Deut
schlandkarte%20Myriophyllum%20heterophyllum.jpg (January 2013)

Page 20
reproductively viable population. The endangered area may be the whole country or part of it where ecological
factors favour the establishment of the organism (consider the spatial distribution of preferred habitats). For non-
native species already established, mention if they are well adapted to the eco-climatic conditions found in
Belgium (F), where they easily form self-sustaining populations, and which areas in Belgium are still available for
future colonisation (G).
A/ Life-cycle and reproduction
Reproduction primarily occurs through vegetative fragmentation and rhizome division,
although the plant may also reproduce by seeds remaining in lake and ponds sediments. The
flowers and fruits appear from June to September (EPPO 2012). Up to now only vegetative
reproduction has been observed and mentioned in Europe (Fritschler 2007, Hussner 2010).
B/ Climatic requirements
3
In North America M. heterophyllum over-winters in the frozen lakes of northern climates and
can thrive in warm southern water bodies. Optimal growth temperature range from 18°C to
25°C. The plant has however been found growing under a wide range of water temperatures
(réf).
C/ Habitat preferences
4
M. heterophyllum primarily occurs in lakes, ponds, large rivers and swamps, but can also
grow in a semi-terrestrial form when stranded on mudflats.
Gerber and Les (1996) found M. heterophyllum to be associated with water bodies that had
higher pH and calcium levels relative to other species of milfoils in Michigan and Wisconsin.
It can be found in calcium-rich waters, but tends to prefer acid waters in Belgium (AlterIAS
web site). In New Hampshire (USA), in its introduced range M. heterophyllum is associated
with large lakes: large, low elevation lakes with relatively high pH, alkalinity and conductivity
(Thum & Lennon, 2009). It is not clear whether these relationships hold true across different
geographic areas where the species occurs, or among distinct genetic lineages of M.
heterophyllum.
D/ Food habits
5
3
 Organism’s capacity to establish a self-sustaining population under Atlantic temperate conditions (Cfb
Köppen-Geiger climate type) should be considered, with a focus on its potential to survive cold periods during
the wintertime (e.g. plant hardiness) and to reproduce taking into account the limited amount of heat available
during the summertime.
4
 Including host plant, soil conditions and other abiotic factors where appropriate.
5

Page 21
NA
E/ Control agents
The aquatic weevil Eubrychius velutus is distributed throughout Europe and Asia. It is a
Myriophyllum specialist. Native hosts are M. verticillatum and M. spicatum. It has expanded
its host range to include the non–native M. heterophyllum. The weevil can complete all life
stages on the plant by living on and consuming the meristem and leaves during larvae stage
up to pupation on the stem. After hatching the adults begin feeding on the meristem and
leaves (Newman et al. 2006).
F/ Establishment capacity in Belgium
On the basis of comparison of natural and climatic conditions prevalent in north-eastern
USA, where the species is aggressively invasive, one should acknowledge that the potential
establishment capacity in Belgium and in neighbouring countries is high.
Nevertheless, in Belgium M. heterophyllum has not yet displayed an invasive behaviour. This
lag phase could be explained for reasons like differences in genetic lineages or by existing
control agents or competitive plants present here and not in north-eastern USA or a
combination of these factors.
 For animal species only.

Page 22
G/ Endangered areas in Belgium
Endangered areas
low risk
medium risk
high risk
Climatic conditions (including severe frost in winter) and natural or semi-natural habitats
where the species occurs in north-eastern USA are pretty similar to the ones observed in
north-western Europe. If the species started to be more aggressive, all Belgian districts would
present the right eco-climatic conditions and could potentially be invaded by the species :
Districts in Belgium
Environmental conditions for species
establishment6
Maritime
Optimal
Flandrian
Optimal
Brabant
Optimal
Kempen
Optimal
Meuse
Optimal
Ardenne
Optimal
Lorraine
Optimal
ESTABLISHMENT CAPACITY AND ENDANGERED AREAS IN BELGIUM
M. heterophyllum is present in the wild and partly naturalized in Belgium and in Europe
but has not yet displayed an invasive behaviour. This could be explained by the presence of
a natural control agent, an aquatic weevil, or differences in genetic lineages or the
presence of competitive plants here but not in north-eastern USA, or a combination of
these factors..
6
 For each district, choose one of the following options : optimal, suboptimal or inadequate.

Page 23
2.1.5 Dispersion capacity
Specify what is the rate of dispersal once the species is released or disperses into a new area. When available,
data on mean expansion rate in introduced territories can be specified. For natural dispersion, provide information
about frequency and range of long-distance movements (i.e. species capacity to colonise remote areas) and
potential barriers for spread, both in native and in introduced areas, and specify if the species is considered as
rather sedentary or mobile. For human-assisted dispersion, specify the likelihood and the frequency of intentional
and accidental movements, considering especially the transport to areas from which the species may easily
colonise unintended habitats with a high conservation value.
A/ Natural spread
Like most other invasive aquatic plants, Myriophyllum heterophyllum is largely spread over
geographically separate regions by human dispersal (mainly through the aquatic plants trade
for aquaria and garden ponds (e.g. Revilla et al., 1991; Kay and Hoyle, 2001; EPPO datasheet
2011). Once established in a new locality, its spread can happen via a range of mechanisms.
The plants are easily spread downstream in the form of vegetative fragments or seed
(though the latter seems much less important than the former (Sidorkewicj et al., 2000) and
seed production has not been observed in Europe yet (Fritschler 2007; Hussner 2010).
Once escaped from an aquarium or cultivated pond, M. heterophyllum is capable of
spreading through vegetative fragments. Vegetative parts of the plant may be spread by
animals especially waterfowl (via the digestive tract or attached to plumage). This is always a
possible mean of transfer from one site to another. There is also possibility of dispersal by
flooding events.
B/ Human assistance
M. heterophyllum is a popular plant in the aquarium and water gardening trades and can
readily be obtained from any number of aquatic plant vendors under a variety of names.
Plants confirmed genetically as M. heterophyllum have been purchased from a variety of
vendors under a variety of common (myrio, foxtail, and parrotfeather) and scientific names
of (M. heterophyllum, M. pinnatum, M. tuberculatum, M. aquaticum, and M. simulans).
Plant fragments are also easily transported attached to ships or boats. In Canada and
elsewhere, quarantine measures have been introduced involving public information
campaigns and boat inspections (for example at ferry landing points on Vancouver Island,
British Columbia) to try to minimize transfer of plant material to un-infested river and lake
systems.
DISPERSAL CAPACITY
The species capacity to colonize new areas is clearly linked to human-mediated dispersion,
mainly through trade and disposal of aquaria contents into local waterways and ponds. In
non-native area, where the species shows invasive characters, short distance dispersal by

Page 24
vegetative means is facilitated by accidental transport on human clothes and footwear,
machinery, boats or fishing equipment.
2.2 EFFECTS OF ESTABLISHMENT
Consider the potential of the non-native organism to cause direct and indirect environmental, economic and social
damages as a result of establishment. Information should be obtained from areas where the pest occurs naturally
or has been introduced, preferably within Belgium and neighbouring areas or in other areas with similar eco-
climatic conditions. Compare this information with the situation in the risk analysis area. Invasion histories
concerning comparable organisms can usefully be considered. The magnitude of those effects should be also
compared with those caused by their closest native relatives.
2.2.1 Environmental impacts
Specify if competition, predation (or herbivory), pathogen pollution and genetic effects is likely to cause a strong,
widespread and persistent decline of the populations of native species and if those mechanisms are likely to affect
common or threatened species. Document also the effects (intensity, frequency and persistency) the non-native
species may have on habitat peculiarities and ecosystem functions, including physical modification of the habitat,
change to nutrient cycling and availability, alteration of natural successions and disruption of trophic and
mutualistic interactions. Specify what kind of ecosystems are especially at risk.
A/ Competition
In north-eastern USA where the species is invasive, dense and extensive populations of M.
heterophyllum cause loss of light and reduction in dissolved oxygen content. This results in a
change of water quality and generally modifies the suitability of habitats for other species. By
this way the plant out-competes and can displace the native aquatic flora(EPPO 2012).
B/ Predation/herbivory
NA
C/ Genetic effects and hybridization
It has been suggested that the invasive character of M. heterophyllum in north-eastern USA is
due to heterosis or “hybrid vigor” resulting from hybridization with other Myriophyllum
species. In Eastern USA, the species may hybridize with the native M. laxum resulting in a
more aggressive hybrid Myriophyllum heterophyllum x laxum (Moody & Les 2002, in Moody
& Les 2010).
Thum & Lennon (2006) question this in their article “Is hybridization responsible for
invasive growth of non-indigenous water-milfoils?” Using nuclear ribosomal DNA,
they looked for F1 hybrid populations of invasive M. heterophyllum in 25 New
Hampshire lakes. In contrast to previous study that found F1 hybrid lineages of invasive M.
heterophyllum in Connecticut, they did not find hybrids in their study lakes. This result has
two implications: (1) pure lineages of M. heterophyllum are also capable of invasive growth,
and (2) the distribution of invasive M. heterophyllum lineages (hybrid vs. pure) may be
spatially structured across New England. Thum & Lennon (2006) stressed the importance

Page 25
of more detailed distributional and ecological studies for understanding the invasive
potential of this species. They also mentioned that it is possible that increased nutrient
inputs and lake disturbances arising from increased recreational use (ie eutrophication of
lakes see Lennon et al. 2003, as cited in Thum & Lennon 2006) might facilitate both their
spread and establishment.
The absence of invasive character observed in European M. heterophyllum populations could
also be linked with the genetic hypotheses. It is well possible that M. heterophyllum lineages
introduced in Europe do not have the favourable characteristics of invasiveness.
Hybridization with native local Myriophyllum sp. has not been observed in Europe but could
happen in the future. There is also a risk that, in the future, new human induced accidental
introductions concern Myriophyllum heterophyllum x laxum or the more aggressive
lineages/strains observed in north-eastern USA.
D/ Pathogen pollution
None known.
E/ Effects on ecosystem functions
In north-eastern USA M. heterophyllum is highly competitive and can grow and spread
rapidly, and is able to outcompete other submerged macrophyte species. It produces dense
mats that reduce sunlight and can restrict water movement, and particularly when in
decomposition, it can reduce water quality and available oxygen. The resulting low oxygen
conditions can then kill fish and harm other aquatic organisms.
ENVIRONMENTAL IMPACTS
Where the species is invasive, observed environmental impacts include habitat alteration,
modification of natural benthic communities, modification of nutrient regimes,
modification of succession patterns. All those impacts could locally lead to a reduction of
native biodiversity, threat to and loss of endangered species. Some infrastructure damage
and damage to ecosystem services have also been mentioned.
None of these impacts have been observed on a large scale in Belgium or Europe yet but it
could happen if the species started to become an aggressive invasive.

Page 26
2.2.2 Other impacts
A/ Economic impacts
Describe the expected or observed direct costs of the introduced species on sectorial activities (e.g. damages to
crops, forests, livestock, aquaculture, tourism or infrastructures).
In north-eastern USA dense mats along lake shorelines have been reported to have reduced
property values by 20-40% (by limitations on water use - recreational activities).
B/ Social impacts
Describe the expected or observed effects of the introduced species on human health and well-being, recreation
activities and aesthetic values.
During extensive growth episode of the plant, dense mats on water can impede recreational
use such as swimming, diving, boating and fishing.

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STAGE 3 : RISK MANAGEMENT
The decision to be made in the risk management process will be based on the information collected during the
two preceding stages, e.g. reason for initiating the process, estimation of probability of introduction and
evaluation of potential consequences of introduction in Belgium. If the risk is found to be unacceptable, then
possible preventive and control actions should be identified to mitigate the impact of the non-native organism and
reduce the risk below an acceptable level. Specify the efficiency of potential measures for risk reduction.
3.1 RELATIVE IMPORTANCE OF PATHWAYS FOR INVASIVE SPECIES ENTRY IN BELGIUM
The relative importance of intentional and unintentional introduction pathways mediated by human activities
should be compared with the natural spread of the organism. Make use e.g. of information used to answer to
question 2.1.3.
International aquarium and horticultural trade is the only introduction pathway identified for
the species entry in Belgium. Used as an aquarium or as an ornamental plant in garden
ponds, M. heterophyllum is relatively rarely encountered within the plant trade in Belgium.
This plant is not considered as economically important by the sector and is sold in less than
10% of nurseries/garden centers in Belgium (totally absent in the Walloon Region)
(Vanderhoeve et al. 2006 ; Halford et al. 2011).
3.2 PREVENTIVE ACTIONS
Which preventive measures have been identified to reduce the risk of introduction of the organism? Do they
reduce the risk to an acceptable level and are they considered as cost-effective? Specify if the proposed measures
have undesirable social or environmental consequences. Consider especially (i) the restrictions on importation and
trade and (ii) the use of specific holding conditions and effect of prohibition of organism introduction into the wild.
As with most of the other Invasive Alien Species, the best way to deal with the threat posed
by Myriophyllum heterophyllum to biodiversity and society is through a combination of
preventive measures, early detection and rapid response to new incursions, with permanent
management only as the last option. It is particularly important for this species which is not
yet invasive in Europe to prevent introduction of more aggressive taxa (genetic lineages or
hybrids).
(i) Prohibition of organism importation, trade and holding
Hussner et al. 2010 consider that the increase in species number and abundance of aquatic
plants is probably caused by enhanced trading and increased invasibility due to water
eutrophication ⁄ re-oligotrophication and climate change. They proposed a trading ban for
highly invasive non-indigenous aquatic plants. We agree with their proposal even if this will
not stop natural spread, it should reduce the risk of further unintended entry and thus can
be a major control factor. Legislation should be strengthened to ensure a ban on import and
possession of potential invasive plants such as M. heterophyllum and closely related species.
Cultural control and sanitary measures are other actions that will effectively limit further
spread of M. heterophyllum in the environment. In this regard, the species has already been
banned in many different states of the USA. It was banned in Connecticut in 2003 (CT

Page 28
invasive plants council http://nbii-
nin.ciesin.columbia.edu/ipane/ctcouncil/CT_Invasive_Plant_List.htm), in Massachusetts as of
January 1, 2006 (possibly earlier) (Massachusetts Dept. of Agriculture Resources
http://www.mass.gov/agr/), in Maine as of September 1, 2000 (Chapter 722 H.P. 1843 – L.D.
2581 = A law in Maine designed to prevent the spread of invasive aquatic plants), in Vermont
as of 2003 (Vermont Dept. of Agriculture http://www.vermontagriculture.com/), in New
Hampshire (NH-DES 2007, in Glomski & Netherland 2008) and banned in the state of
Washington as of 2005 (Washington Administrative Code title 16, chapter 16-750). In Europe,
it is advised to amend and/or reinforce regulations in order to ban this species from personal
holding and commercial trades.
(ii) Use of specific holding conditions and effect of prohibition of organism introduction into
the wild
So far preventive management efforts have focused on the establishment of laws that
require removing plant debris from boats and trailers (Thum & Lennon 2006). Such measures
will prevent plant fragments to be disseminated and enhance further spread.
3.3 CONTROL AND ERADICATION ACTIONS
Which management measures have been identified to reduce the risk of introduction of the organism? Do they
reduce the risk to an acceptable level and are they considered as cost-effective? Specify if the proposed measures
have undesirable social or environmental consequences. Consider especially the following questions.
(i) Can the species be easily detected at early stages of invasion (early detection)?
In its native range M. heterophyllum may be confused with a number of Myriophyllum
species. In general species of Myriophyllum are distinguished by characters of flowers and
fruits, which may not be present. Vegetative material of M. heterophyllum may especially be
confused with closely related species M. humile, M. farwelli, M. pinnatum, M. laxum, and M.
hippuroides. However, misidentifications with more distantly related species also occur
(Aiken, 1981; Thum et al., 2006), especially M. verticillatum.
Genetic identifications using the nuclear ribosomal DNA Internal Transcribed Spacer regions
(ITS) have become common (Moody and Les, 2002; Thum et al., 2006). However, further
work on the reliability of these markers based on much larger sample sizes is needed.
In Belgium and north-western Europe the only potentially confusing species is M. aquaticum
due to its similar emerging stems (it is in any case another invasive species).
(ii) Are they some best practices available for organism local eradication?
The side effect of chemicals and even biological control methods can often be as
detrimental or even worse for the environment, native species and human health.

Page 29
The precautionary principle should be applied as a general rule.
Several practices, means of control and means of avoiding further spread and in some cases
means of eradication of M. heterophyllum do exist:
- Manual: Hand-pulling or tarpauling may control infestations (Washington State
Noxious Weed Control Board 2007). Hand removal and benthic mat use were more effective
than cutting at eight infested lake sites in Maine (Bailey et al. 2008). Benthic mats are an
appropriate option for thick extensive infestations, whereas hand removal is more cost-
effective and more efficient in small areas with high-density infestations or for selective
removal of sparse infestations in native macrophytic strands.
- Physical: Drawdown can also be used to control M. heterophyllum where applicable
if it is extensive enough to prevent re-growth from seeds (EPPO 2009). This control method
could have a negative impact on native plants and animals (EPPO 2009).
- Chemical: Similar to fluridone, newer chemicals tend to be enzyme-specific
compounds with a reduced impacts on non-target species (Getsinger et al. 2008). Diquat
dibrominde (Reward) and 2,4-D (Aqua Kleen and Navigate) are currently approved for use in
most states in North America (Washington State Noxious Weed Control Board 2007).
Triclopyr may be another option. Results from Getsinger et al. (2003) suggest that triclopyr
may be efficacious against M. heterophyllum in the field over a wide range of concentrations
and exposure times. Glomski and Netherland (2007) found that diquat at 370 μg ai L-1 for 30
hours provided good control (85%) of M. heterophyllum and that all rates and exposures of
carfentrazone significantly reduced M. heterophyllum biomass, however, shoot regrowth
from root crowns required follow-up applications. Fluridone and penoxsulam were also
reported to control M. heterophyllum at rates as low as 5 and 10 µg ai L-1 respectively
(Glomski & Netherland 2008).
- Biocontrol: Sheldon and Creed (2003) found that the North American weevil
Euhrychiopsis lecontei being used as a biological control agent for Eurasian watermilfoil (M.
spicatum) is a specialist herbivore which will have little impact on the survival of M.
heterophyllum. In Europe the aquatic weevil Eubrychius velutus feeds on the meristem and
leaves of diverse Myriophyllum including M. heterophyllum and has potential as a biological
control agent. Further research is necessary in this domain.
(iii) Do eradication and control actions cause undesirable consequences on non-target
species and on ecosystem services ?
The use of physical removing, drawdown, shading, introduction of control agents or
herbicide treatment have resulted in eradication with various degree of success in particular
situations. However, these means of control are non-specific . Either one of these actions will
inevitably cause serious damage to local flora or fauna by intoxication (in case of chemical
control), habitat disturbance and ecosystem service alteration. These side effects could

Page 30
indeed drastically affect native submerged vegetation and aquatic fauna (fish, reptiles,
amphibians, etc.).
(iv) Could the species be effectively eradicated at early stage of invasion?
Low, recently detected infestations may be successfully eradicated through careful and
thorough hand-pulling or by using a tarpaulin. Great care should be taken with such methods
since they can cause fragmentation of the plant and therefore may enhance its spread.
(v) If widely widespread, can the species be easily contained in a given area or limited under
an acceptable population level?
Total eradication after extensive establishment is unlikely. In some particular cases (e.g. in
shallow lakes in Nordrhein-Westfalen (Germany) dense stands have been successfully
controlled. Benthic barriers may be used in small areas (swimming beaches, boating lanes,
around docks) to restrict light and upward growth. Nevertheless, barriers can have a negative
impact on benthic organisms and need to be properly maintained. Drawdown can also be
used to control M. heterophyllum where applicable, if it is extensive enough to prevent re-
growth from seeds.
BEST MANAGEMENT MEASURES
As with most of the other Invasive Alien Species, the best way to deal with the threat
posed by Myriophyllum heterophyllum to biodiversity and society is through a
combination of preventive measures, early detection and rapid response to new
incursions, with permanent management only as the last option.
It is particularly important for this species, which is not yet invasive in Europe, to prevent
new introduction of more aggressive taxa (genetic lineages or hybrids). It is advised to
amend and/or reinforce regulations in order to ban completely this species from personal
holding and commercial trades.

Page 31
LIST OF REFERENCES
Aiken, S.G. (1981). A conspectus of Myriophyllum (Haloragaceae) in North America. Brittonia 33: 57-69.
ANSES - Agence nationale de sécurité sanitaire de l’alimentation, de l’environnement et du travail. (2011). Note
d’alerte initiale sur Myriophyllum heterophyllum - 2 septembre 2011.
Bailey, J.E. & Calhoun, A.J.K. (2008). Comparison of three physical management techniques for controlling
variable-leaf milfoil in Maine Lakes. Journal of Aquatic Plant Management 46: 163-167.
Bouxin, G. & Lambinon, J. (1996). Deux xénophytes aquatiques nouveaux pour la Belgique, Myriophyllum
heterophyllum et Lagarosiphon major, dans la Meuse à Lives-sur-Meuse (province de Namur). Nat.
Mosana 49: 94-97.
De Beer, D. & De Vlaeminck, R. (2008). Myriophyllum heterophyllum, een nieuwe invasive waterplant. Dumortiera
94: 8-13.
EPPO. (2009). Data sheets on plant quarantine pests – Myriophyllum heterophyllum (09-15152).
EPPO. (2011). EPPO Reporting Service. EPPO Reporting Service. Paris, France: EPPO.
http://archives.eppo.org/EPPOReporting/Reporting_Archives.htm
EPPO. (2012). http://www.eppo.int/INVASIVE_PLANTS/iap_list/Myriophyllum_heterophyllum.htm [consulted December
2012].
FloraWeb. (2009). http://www.floraweb.de/pflanzenarten/cg_floramap/cg_floramap.html
Fritschler, N. (2007). Regenerationsfähigkeit von indigenen und neophytischen Wasserpflanzen. Diplomarbeit,
Abt. Geobotanik, Heinrich-Heine-Universität Düsseldorf, 72 S.
Gerber, D. & Les D. (1996). Habitat differences among seven species of Myriophyllum (Haloragacea) in W isconsin
and Michigan. Michigan Botanist 35: 75-86.
Getsinger, K.D., Netherland, M.D., Grue, C.E. & Koschnick, T.J. (2008). Improvements in the use of aquatic
herbicides and establishment of future research directions. Journal of Aquatic Plant Management 46:
32-41.
Glomski, L.M. & Netherland, M.D. (2008). Efficacy of Fluridone, Penoxsulam, and Bispyribac-sodium on Variable-
leaf Milfoil. Journal of Aquatic Plant Management 46: 193-196.
Halford, M., Heemers, L., Mathys, C., Vanderhoeven, S. & Mahy, G. (2011). Enquête socio-économique sur les
plantes ornementales invasives en Belgique. Rapport du projet AlterIAS au programme Life+
«Information et Communication ».
Halstead, J.M., Michaud, J., Hallas-Burt, S. & Gibbs, J.P. (2003). Hedonic analysis of effects of a nonnative invader
(Myriophyllum heterophyllum) on New Hampshire lakefront properties. Environmental Management 32:
391-398.
Hussner, A. (2008). Okologische und ökophysiologische Charakteristika aquatischer Neophyten in Nordrhein-
Westfalen. PhD dissertation, University of Düsseldorf.
Hussner, A. (2010). Invasive alien species fact sheet Myriophyllum heterophyllum. From online database on
aquatic neophytes in Germany.
Hussner, A., Nienhaus, I. & Krause, T. (2005). [Distribution of Myriophyllum heterophyllum Michx. in North Rhine-
Westphalia] (Zur Verbreitung von Myriophyllum heterophyllum Michx. in Nordrhein-Westfalen).
Floristische Rundbriefe 39: 113-120.
Jäger, E.J., Ebel, F., Hanelt, P. & Müller, G. (eds.) (2008). Rothmaler Band 5. Exkursionsflora von Deutschland.
Krautige Zier- und Nutzpflanzen. Springer Verlag, Berlin: 880 p.

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Kay, S.H. & Hoyle, S.T. (2001). Mail order, the Internet, and invasive aquatic weeds. Journal of Aquatic Plant
management 39: 88-91.
Les, D.H., Mehrhoff, L.J. (1999). Introduction of nonindigenous aquatic vascular plants in Southern New England: a
historical perspective. Biological Invasions 1(2/3): 281-300.
Luijten, S. & Odé, B. (2007). Status en het voorkomen van een aantal belangrijke invasieve plantensoorten in
Nederland. Floron rapport 47.
Moody, M.L. & Les, D.H. (2002). Evidence of hybridity in invasive watermilfoil (Myriophyllum) populations.
Proceedings of the National Academy of Sciences of the United States of America 99(23): 14867-14871.
NatureServe (2009) Myriophyllum heterophyllum. From NatureServe Explorer, an online encyclopedia of Life.
Newman, R.M., Gross, E.M., Wimmer, W. & Sprick, P. (2006). Life history and developmental performance of the
Eurasian milfoil beetle, Eubrychius velutus (Coleoptera: Curculionidae). Coleopterist’s Bulletin 60: 170-
176.
Onion, A. (2004). Herbivore resistance in invasive and native Myriophyllum spicatum and Myriophyllum
heterophyllum. PhD thesis presented to the Faculty of the Graduate School of Cornell University.
Pot, R. (2007). Over de aanpak van de woekering van ongelijgbladig vederkruid en waterwaaier in het
Oranjekanaal. Oosterhesselen.
Revilla, E. P., Sastroutomo, S. S. & Rahim, M.A.A. (1991). Survey on aquarium plants of quarantine importance and
their associated nematodes. BIOTROP Special Publication No. 40. pp. 205-215. BIOTROP, Bogor,
Indonesia.
Sheldon, S. P. , Creed, R.P. Jr. (2003). The effect of a native biological control agent for Eurasian watermilfoil on six
North American watermilfoils. Aquatic Botany 76(3): 259-265.
Sidorkewicj, N.S., Sabbatini, M.R. & Irigoyen, J.H. (2000). The spread of Myriophyllum elatinoides Gaudich. and M.
aquaticum (Vell.) Verdc. from stem fragments. In Légère, A. (ed.), Abstracts of the Third International
Weed Science Congress. International Weed Science Society, Oregon: 224–225.
Stiers, I., Crohain, N., Josens, G. & Triest, L. (2009) Impact of aquatic invasive species on native plant and benthic
macro-invertebrate assemblages in Belgian ponds. Poster in Branquart, E. & Segers, H. (Eds), Abstract
volume of the Science facing Aliens Conference, Brussels: 52.
Thum, R.A. & Lennon, J.T. (2006). Is hybridization responsible for invasive growth of non-indigenous water-
milfoils? Biological Invasions 84: 1061-1066.
Thum, R.A., Lennon, J.T., Connor, J. & Smagula, A.P. (2006). A DNA fingerprinting approach for distinguishing
native and non-native milfoils. Lake and Reservoir Management 22: 1-6.
Thum, R.A. & Lennon, J.T. (2010). Comparative ecological niche models predictive the invasive spread of variable-
leaf milfoil (Myriophyllum heterophyllum) and its potential impact on closely related native species.
Biological Invasions 12: 133-143.
Thum, R.A., Zullig, M.P., Johnson, R.L., Moody, M.L. & Vossbrinck, C. (2011) Molecular markers reconstruct the
invasion history of variable leaf watermilfoil (Myriophyllum heterophyllum) and distinguish it from
closely related species. Biological Invasions 13: 1687-1709.
Vanderhoeven, S., Pieret, N., Tiebre, M.-S., Dassonville, N., Meerts, P. , Rossi, E., Nijs, I., Pairon, M., Jacquemart, A.-
L., Vanhecke, L., Hoste, I., Verloove, F. & Mahy, G. (2006). INPLANBEL: Invasive plants in Belgium:
Patterns, processes and monitoring. Scientific support plan for a sustainable development policy SPSD 2.
Final report, 94 pp.
Verloove, F. (2006) Catalogue of the Neophytes in Belgium (1800-2005). Scripta Botanica Belgica 39, 89 pp.

Page 33
Wann, J.D. (1997). Myriophyllum. In: Cullen J. & al. (eds.). The European Garden Flora, vol. 5. Cambridge
University Press, Cambridge: 358.
Washington State Noxious Weed Control Board (2007). Washington State noxious weed list. Washington State
noxious weed list. unpaginated. http://www.nwcb.wa.gov
Wimmer, W. (1997). Myriophyllum heterophyllum Michaux in Lower Saxony and Bremen and determination key
for the vegetative stage. Floristische Rundbriefe. 31(1): 23-31.
Yu, D., Wang, D., Li, Z.Y. & Funston, A.M. (2002, publ. 2003). Taxonomic revision of the genus Myriophyllum
(Haloragaceae) in China. Rhodora 104(920): 396-421.
Internet sites consulted
FloraWeb (2009). http://www.aquatischeneophyten.de/Übersicht aquatische Neophyten.htm
http://alienplantsbelgium.be/content/myriophyllum-heterophyllum-0
http://www.aquatischeneophyten.de/Bilder/Verbreitungskarten%20deutsche%20Version/Deutschlandkarte%20
Myriophyllum%20heterophyllum.jpghttp://www.cabi.org/isc/?compid=5&dsid=34940&loadmodule=datasheet&
page=481&site=144
http://www.issg.org/database/species/references.asp?si=1700&fr=1&sts=&lang=EN
http://www.invasive.org/browse/detail.cfm?imgnum=5308025
http://observations.be
http://www.eppo.int/INVASIVE_PLANTS/iap_list/Myriophyllum_heterophyllum.htm