Salvinia molesta | Sailvín mhór

Pre 2017

2017 - 2020


Legal status

Regulated invasive species of Union concern under the European Regulation on the prevention and management of the introduction and spread of invasive alien species [1143/2014].

Third Schedule listed species under Regulations 49 & 50 in the European Communities (Birds and Natural Habitats) Regulations 2011. (Note: Regulation 50 not yet enacted).

Listed as a schedule 9 species under Articles 15 & 15A of the Wildlife Order (Northern Ireland) 1985 (Article 15A not yet enacted).

First reported in the wild



Invasive species - risk of High Impact

Irish status


Introduction pathways - 1

Escape from Confinement

Introduction pathways subclass - 1

Landscape/flora/fauna improvement

Introduction pathways - 2

Transport Contaminant

Introduction pathways subclass - 2

Contaminant nursery material

NAPRA Ireland risk assessed


Species Biology


Salvinia molesta is a species of perennial plant in the family Salviniaceae (floating herbs) that is associated with freshwater habitats (Encyclopedia of Life, 2021). This species is a free-floating aquatic plant with short green leaves arranged in whorls of three (two upper and one lower) (Invasive Species Ireland, 2021). Salvinia molesta is a mat-forming species that can be up to 30 cm long, 5 cm wide and over 2.5 cm thick (CABI, 2021). The short, round upper leaves are 0.7-3 cm long and 1.8 cm wide (CABI, 2021). These leaves are photosynthetic (CABI, 2021). The lower leaves are 1.5-2 cm long and 0.5 cm wide (CABI, 2021). They lie submerged in the water and are non-photosynthetic (CABI, 2021).


Salvinia molesta can act as either a perennial or annual depending on the climatic conditions of the habitat it is found in (Global Invasive Species Database, 2021).This species passes through three different growth stages throughout its lifecycle. The first stage is known as primary growth and sees the growth of single ramets (plantlets) (Global Invasive Species Database, 2021). The next stage is known as the secondary growth stage and sees the growth of a linear chain of ramets (Global Invasive Species Database, 2021). The final stage is known as the tertiary stage and sees the formation of a compact cluster of biomass (Global Invasive Species Database, 2021).


Salvinia molesta will grow best in habitats that provide high light intensities, high nutrient availability and relatively high water temperatures (CABI, 2021). If temperatures drop to as low as -3ºC, the terminal buds of this species can be damaged and the plant may die (CABI, 2021). Salvinia molesta is a freshwater species and has little tolerance for saline conditions (CABI, 2021).


Biodiversity - The way in which Salvinia molesta grows will often lead to the formation of dense mats of vegetation that cover the surface of the water (Chapman et al., 2017). These mats of biomass may lead to decreased photosynthesis and, by extension, decreased dissolved oxygen levels, increased sedimentation through decreased water flow, and altered pH, carbon dioxide and hydrogen sulphide levels (Chapman et al., 2017). 

The mono-specific growth dominating an area can also negatively influence invertebrates, fish and waterfowl, which can permanently alter trophic dynamics (the way energy is transferred between trophic levels in an ecosystem) in the system (Chapman et al., 2017).

Ecosystem services - Provisioning services may be negatively affected as decomposition of Salvinia molesta can influence water quality and availability. This could result in stress exertion on fish stocks (Chapman et al., 2017). 

Regulating services can be impacted as native biodiversity is outcompeted, aquatic systems are altered and dense mats of vegetation can block engineering structures (Chapman et al., 2017).

The rapid growth rate of Salvinia molesta combined with its slow rate of decomposition may negatively impact nutrient cycling and primary production, adversely affecting supporting services within the system (Chapman et al., 2017). 

The dense, mono-specific mats of vegetation produced by this species may limit access to water for recreational activities such as swimming and boating, resulting in a negative influence on cultural services within an area (Chapman et al., 2017). Moreover, the loss of biodiversity and species richness resulting from the mono-specific mats of vegetation can hurt the aesthetics of a natural area (Chapman et al., 2017).

Economic - Salvinia molesta invasion can bring about a multitude of economic impacts such as interference with weirs, floodgates and locks; flooding due to blocked drains; preventing livestock reaching drinking water; and generally degrading water quality (Chapman et al., 2017). 


Salvinia molesta is associated with slow flowing or stagnant waters such as lakes, low energy rivers or streams, wetlands, irrigation channels, ditches, ponds and canals (Chapman et al., 2017).

Mechanism of impact


Management approach


As Salvinia molesta is listed as an Invasive Alien Species of Union concern under the EU Regulations of Invasive Alien Species, it cannot be imported, traded, or released to the wild. Measures must also be taken to prevent spread of existing populations of it (European Commission, 2017).

The public should be urged to use the Check Clean Dry protocol on their equipment and clothing when moving between water bodies to prevent contamination (Invasive Species Ireland, 2021).

Early detection of an invasive species within a country will allow for a much greater chance of successfully controlling its spread before it can become fully established. Early detection will allow for trained personnel to swiftly address the issue at hand (van Valkenburg, 2017). The use of Citizen Science can be a powerful tool to aid in early detection of invasive alien species as the public can be shown what to look for and have a place that they can log possible sightings of invasive species. This will decrease the chances of an invasive species going unnoticed.

Mechanical control

It is possible to manually remove this species from an area through the use of drag nets, pitch forks etc. but this may only be feasible in the early stages of an infestation on smaller sites (van Valkenburg, 2017). The chances of totally controlling the spread of this species on larger sites or in late stages of infestation are very slim (van Valkenburg, 2017). Where this control method is implemented, removed biomass should be dried, burnt or buried in order to prevent its accidental re-establishment (van Valkenburg, 2017). Moreover, ongoing monitoring should be implemented in order to detect and treat re0infestations at later dates (van Valkenburg, 2017).

Chemical control

Herbicide use can be a highly effective method for controlling invasive plant species but as Salvinia molesta is aquatic, strict measures need to be implemented in order to avoid unnecessary damage to the surrounding aquatic environment. Herbicides such as glyphosate can be used to control this species but they have not resulted in complete eradication of Salvinia molesta (van Valkenburg, 2017). The high cost associated with ongoing chemical treatment, combined with the fact that it does not guarantee eradication of Salvinia molesta, means that chemical control on its own may not be a feasible approach (van Valkenburg, 2017).

Integrated control

Integrated control is the concept of combining two or more control methods in order to control the target species to a higher degree than any of the individual controls would achieve on their own. An example would be to use both physical and chemical together by manually removing as much biomass as possible and then spraying the remaining plant material (van Valkenburg, 2017). In theory, this will result in a higher level of control than just implementing manual or chemical control on their own. Even with this multi-faceted approach, ongoing monitoring and subsequent control over the following years may be required to prevent re-establishment.

Species group


Native region

South America


World distribution(GBIF)

In addition to its native distribution of south-eastern Brazil, Salvinia molesta has spread through many parts of the world where it is becoming an alien invasive species (Chapman et al., 2017). This species can be found throughout Africa, Central and South America, Asia, North America, Europe and Oceania. In many countries where it has established populations, it has become locally invasive and continues to spread (Chapman et al., 2017).

Irish distribution

Not present.

Temporal change

Records submitted to Data Centre in 2024

The following map is interactive. If you would prefer to view it full screen then click here.

How can you help

Report any sightings of this species to the National Biodiversity Data Centre, including a photograph, if possible.

Dispose of unwanted specimens in a responsible manner that does not allow them in to the natural environment.

Avoid purchasing this species for ornamental purposes.



CABI, 2021. Salvinia molesta (kariba weed). [online] Available at: <> [Accessed 14 Jul. 2021].

Chapman, D., Coetzee, J., Hussner, A., Netherland, M., Newman, J., Pescott, O., Stiers, I., Van Valkenburg, J. and Tanner, R., 2017. Pest Risk assessment for Salvinia molesta. [online] Paris. Available at: <> [Accessed 14 Jul. 2021].

Encyclopedia of Life, 2021. Salvinia molesta. [online] Available at: <> [Accessed 14 Jul. 2021].

European Commission, 2017. Invasive Alien Species of Union concern. [online] Luxembourg. Available at: <> [Accessed 25 Jun. 2021].

Global Invasive Species Database, 2021. Salvinia molesta. [online] Available at: <> [Accessed 14 Jul. 2021].

Invasive Species Ireland, 2021. Salvinia molesta. [online] Available at: <> [Accessed 14 Jul. 2021].

van Valkenburg, J., 2017. Information on measures and related costs in relation to species considered for inclusion on the Union list. [online] Available at: < Salvinia molesta.pdf> [Accessed 14 Jul. 2021].