What is Myriophyllum aquaticum and why is it an invasive plant?
Myriophyllum aquaticum, commonly known as "foxtail" or "Brazilian kite", is a perennial aquatic plant belonging to the Haloragaceae family. Native to South America, mainly the Amazon basin, this species has been introduced to various continents and has become naturalized in temperate, warm, tropical and subtropical zones around the world, becoming one of the most problematic invasive plants globally.
Morphological Characteristics Myriophyllum aquaticum includes thick, sometimes hollow stems capable of reaching large floating or slightly emergent extensions. Its leaves, arranged in whorls of 3 to 6, have a pectiniform appearance, are deep green in color and have numerous thin segments, giving it a characteristic feathery appearance. In nature, it flowers in the warm season, although the formation of tiny, predominantly female flowers is generally observed outside South America. Outside its native range, reproduction occurs asexually by fragmentation, that is, from pieces of stem or roots that generate new plants.
The expansion of Myriophyllum aquaticum has been accelerated by its ornamental use both in aquatic gardening and in aquariophilia. However, its great propagation capacity and the absence of natural predators outside their native habitat have caused their presence to be a threat in many environments. serious threat to native aquatic ecosystemsIt is considered one of the most harmful invasive alien species in freshwater systems due to its high growth rate and ability to adapt to different environmental conditions.
Distribution and preferred habitats of Myriophyllum aquaticum
Myriophyllum aquaticum It thrives in shallow aquatic habitats, such as lakes, ponds, lagoons, canals, slow-flowing streams, and slow-flowing rivers. It adapts easily to surface and eutrophicated waters, showing tolerance to a certain level of salinity, which expands the range of environments in which it can establish. In invaded areas, it usually forms dense floating colonies or those attached to the substrate, where its roots are anchored in soft soil and develop in the lowest part of the channel. Some of its stems and leaves remain submerged, while other leaves emerge up to 40 cm above the surface.
Its natural distribution It ranges from South America, especially Brazil and the Amazon basin, but due to its popularity as an ornamental plant, it has been introduced to North America, Europe, Asia, Africa and Oceania. In Europe, its presence has been confirmed in countries such as France, Germany, the United Kingdom, the Netherlands, Portugal, Austria and Spain. In the Iberian Peninsula, official records place it in very specific areas, such as Pontevedra, Barcelona, Álava and Catalonia, although its expansion potential is high, and control experiences reveal that any small fragment can cause new outbreaks.
In Spain, the main affected areas They correspond to aquatic systems with little or no flow, especially in environments altered by human activities, such as irrigation ponds, artificial canals, and lagoons near agricultural or urban areas. Their ability to thrive in nutrient-rich waters and environments subject to moderate salinity variations makes them a latent threat to multiple lotic and lentic habitats.
Ecological impact and problems associated with the invasion of Myriophyllum aquaticum
Physical alteration of aquatic ecosystems: Myriophyllum aquaticum drastically reduces the penetration of sunlight into the water, altering the balance of plant communities and limiting the growth of native aquatic speciesIts dense carpet favors the sedimentation of materials and modifies the dynamics of the bottom, altering the physicochemical conditions of the water.
Changes in biodiversity: The displacement of native vegetation and the alteration of the substrate significantly affect invertebrate and fish communities. Furthermore, by impeding the development of native plants, it limits the availability of shelter and food for local fauna.
Promotion of pests and diseases: By providing shelter for the proliferation of mosquito larvae, their presence can increase the incidence of health problems linked to these insects, which serve as vectors of diseases in humans and animals.
Obstruction of human uses: The exuberant growth of Myriophyllum aquaticum can hamper recreational, fishing, and boating activities and cause blockages in irrigation and drainage systems, resulting in significant economic costs for water management and agriculture.
The problems associated with its overpopulation are internationally recognized and have led to various control and prevention strategies, both locally and regionally. This species is resistant to conventional herbicides, and mechanical removal poses significant risks, as fragmentation facilitates its spread and regeneration in new foci.
Pathways of introduction and spread of the species
La main entry route The main focus of Myriophyllum aquaticum in European and Mediterranean aquatic ecosystems is the ornamental trade and aquariophilia. The plants are purchased for ponds, fountains, and aquariums, but improper disposal or accidental escape of plant fragments contributes to their dispersal into the natural environment. Once in the environment, the species exhibits a very high capacity for vegetative propagation through stem fragments, which can be transported by water, animals or human activities (such as cleaning or maintenance of canals and ponds).
The absence of natural enemies outside of South America, where specialized insects can limit its spread, further favors the species' proliferation in its invaded areas. In regions such as Florida and certain subtropical zones, some beetles of the Alticini tribe have demonstrated an ability to attack the plant, but in Europe and the Iberian Peninsula, these predators are absent, facilitating the massive takeover of habitats.
Legal regulation and control measures in Spain and the European Union
Myriophyllum aquaticum is included in the Spanish Catalogue of Invasive Alien Species, regulated by Royal Decree 630/2013. Their introduction, possession, transportation, trade and release into the natural environment are strictly prohibited.At the EU level, the species is listed as an exotic species of concern under European regulations, which requires all member states to establish specific management and control measures, including protocols for monitoring, eradication, and restoration of affected habitats.
- Spanish Catalogue of Invasive Alien Species: It recognizes its ecological danger and prohibits it throughout the national territory, imposing sanctions and management obligations for administrations and individuals.
- Regulation of the European Union: Listed among the species of greatest concern, this requires periodic monitoring, reporting of new outbreaks, and implementing recommended control and eradication measures.
These legal provisions have led to the development of fact sheets, eradication plans and management guidelines by the relevant agencies. For example, the Ministry for Ecological Transition and the autonomous communities have developed action protocols for addressing outbreaks and preventing new cases.
Examples of control and management of Myriophyllum aquaticum in Spain
The management of Myriophyllum aquaticum is challenging due to its high capacity for vegetative regenerationBelow are some examples of actions in different Spanish regions:
- Lopidana (Álava): After detecting a outbreak in a lagoon connected to the Zadorra River, the decision was made to act without using mechanical or chemical techniques, opting instead to cover the affected area with biodegradable jute matting to block out light and promote crushing and death of the plant. Regular monitoring has been carried out to confirm its effectiveness and prevent regrowth.
- El Montnegre and El Corredor Park (Barcelona): In the El Molinot reservoir the following were carried out: integrated actions These included partial and total emptying of the reservoir, rescue and relocation of native fish, dredging of sediments with heavy machinery, and frequent manual removal of the plant. Despite these efforts, it was proven difficult to completely eradicate the species, as even a small fragment can generate new outbreaks. Days of manual removal proved ineffective, and only extreme solutions such as prolonged drying of the reservoir could be definitive, although their costs are often unaffordable.
- Catalonia and other communities: In areas with small outbreaks, measures such as temporary drainage of ponds, geotextile covering, and the establishment of physical barriers downstream to prevent dispersal during mechanical work have been tested. In addition, the possibility of biologic control through the use of specialized insects, although these methods are still in the experimental phase in Europe.
It is essential that these types of actions be accompanied by long-term monitoring plans, as the plant can remain dormant and regenerate in the aftermath of interventions. Public support, collaboration between administrations, and adequate information for owners and users of aquatic environments are key to the success of these projects.
Protocols and guidelines for prevention and control
- Avoid fragmentation: Mechanical removal of Myriophyllum aquaticum must be carried out with extreme caution, as stem fragmentation is the main route of expansion into new areas. It is recommended to place physical barriers downstream to intercept fragments and repeat the work in subsequent campaigns.
- Selective manual deletion: In small areas, manual removal can be effective if performed accurately and plant debris is properly destroyed to prevent re-invasion.
- Drying and shading: Methods such as controlled drying of the aquatic environment or prolonged covering with opaque materials (geotextile, jute) can deprive the plant of light, promoting its weakening and death.
- Biologic control: Although still in the research phase on the Iberian Peninsula, the introduction of natural predators has shown some success in other areas. However, the potential impacts must be carefully assessed before implementation.
- Do not use non-specific herbicides: Given the environmental risk and low effectiveness on the species, the use of general chemicals in aquatic ecosystems is strongly discouraged.
- Sediment management: After extraction, it is necessary to properly manage the affected sediments and prevent their discharge into areas where new vegetation sources may develop.
Keys to the identification and differentiation of Myriophyllum aquaticum
Correct species recognition is essential to prevent its spread. Myriophyllum aquaticum can be differentiated from other native species of the genus Myriophyllum by:
- Leaves in pectinate whorls, mostly emergent, 2 to 5 cm, with 10 to 18 segments per side.
- Thick stems and often hollow, extending both submerged and floating.
- Tiny, unisexual flowers, rarely produced outside the original areaIn European environments, plants tend to be female, so sexual reproduction is almost non-existent and vegetative propagation predominates.
- Fruit of 1 to 2 mm, which is divided into 4 nutlets.
- Intense light green color and soft texture compared to more rigid native species.
Importance of environmental education and citizen collaboration
The control and prevention of invasive species such as Myriophyllum aquaticum depend largely on the information, awareness and responsibility of society. It is essential to inform gardeners, merchants, aquatic space managers, and the public about the risks involved in using and releasing this plant outside its controlled environment.
- Never release plant remains or fragments into natural channels or ponds..
- Notify the authorities of the presence of suspicious specimens in natural or urban environments, to activate the relevant control protocols.
- Participate in environmental volunteer campaigns aimed at the maintenance and monitoring of aquatic habitats.
- Request technical advice in case of detection of possible invasion foci or for the management of irrigation facilities, ponds and canals.
Citizen collaboration has been key to the early detection of new outbreaks and the success of projects to eradicate and restore affected aquatic ecosystems.
Scientific references and thematic resources for further information
- Canary Islands Biodiversity Data Bank: Myriophyllum aquaticum sheet
- Guide to Exotic and Invasive Species of the Rivers, Lakes and Estuaries of the Iberian Peninsula, LIFE INVASAQUA Project
- Ministry for Ecological Transition – Action sheets and protocols
- EPPO Global Database for international distribution and alerts
- List and protocols for action in autonomous communities such as Catalonia, Aragon, and Galicia
Scientific literature and specific data sheets contain control experiences, identification keys, and protocols that can be consulted to implement interventions tailored to each particular case.
Due to its invasive potential, its rapid spread capacity and the serious impacts it generates on biodiversity and ecosystem services, Myriophyllum aquaticum requires a coordinated, rigorous and sustained actionMaintaining vigilance, implementing good practices, and strengthening environmental education will be crucial to minimizing the threats posed to Iberian and European aquatic ecosystems.