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   Salvinia molesta (aquatic plant, herb)  français     
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      Foliage (Photo: USDA APHIS - Oxford, North Carolina Archives, www.forestryimages.org) - Click for full size   Giant salvinia forms mats up to 2 feet thick, gobbles up oxygen and blocks sunlight needed by other water dwellers (Photo: Scott Bauer, USDA ARS, www.forestryimages.org) - Click for full size   Primary form of giant salvinia (Photo: Mic H. Julien, Commonwealth Scientific and Industrial Research Organization, www.forestryimages.org) - Click for full size   Secondary form of giant salvinia (Photo: Mic H. Julien, Commonwealth Scientific and Industrial Research Organization, www.forestryimages.org) - Click for full size   Tertiary form of giant salvinia (Photo: Mic H. Julien, Commonwealth Scientific and Industrial Research Organization, www.forestryimages.org) - Click for full size   covering a farm pond restricts commercial and recreational use and degrades aesthetics (Photo: Ted D. Center, USDA ARS, www.forestryimages.org) - Click for full size   The hairs form an   Close up of giant salvinia plants (Photo: Scott Robinson, Georgia Department of Natural Resources, www.forestryimages.org) - Click for full size   Closeup with a quarter for size reference (Photo: Scott Robinson, Georgia Department of Natural Resources, www.forestryimages.org) - Click for full size
    Taxonomic name: Salvinia molesta D. S. Mitchell
    Synonyms: Salvinia auriculata Aubl.
    Common names: African payal , African pyle, aquarium watermoss (English-United States), fougère d’eau (French-Burkina Faso), giant salvinia (English-United States), giant salvinia (English), kariba weed (English), koi kandy, salvinia (English), water fern (English), water spangles (English)
    Organism type: aquatic plant, herb
    Salvinia molesta is a floating aquatic fern that thrives in slow-moving, nutrient-rich, warm, freshwater. A rapidly growing competitive plant, it is dispersed long distances within a waterbody (via water currents) and between waterbodies (via animals and contaminated equipment, boats or vehicles). It is cultivated by aquarium and pond owners and it is sometimes released by flooding, or by intentional dumping. S. molesta can form dense vegetation mats that reduce water-flow and lower the light and oxygen levels in the water. This stagnant dark environment negatively affects the biodiversity and abundance of freshwater species, including fish and submerged aquatic plants.Salvinia invasions can alter wetland ecosystems and cause wetland habitat loss. Salvinia invasions also pose a severe threat to socio-economic activities dependent on open, flowing and/or high quality waterbodies, including hydro-electricity generation, fishing and boat transport.
    S. molesta in 2013 was elected as the one of the '100 of the World's Worst Invasive Alien Species' to replace the Rinderpest virus which was declared eradicated in the wild in 2010
    Description
    Salvinia molesta is a free floating aquatic fern. It produces a horizontal rhizome (that lies below the water surface) and two types of fronds (buoyant and submerged). The mature plant produces egg-shaped spore sacs containing infertile spores. It lacks true roots but its submerged fronds function as roots. Its fronds are in whorls of three (two floating and one submerged). The floating fronds are positioned in an opposite orientation to each other and are round to oblong in shape. On their upper surface they have rows of cylindrical papillae. Each papilla has four hairs at its distal end (each consisting of a single row of cells) that are joined together at their tips to form what looks like an inverted egg-beater. The cage-like structure of the end hairs is an effective air trap giving the plant buoyancy in the water. The papillae, end hairs and upper surface of the plant are water repellent in comparison to the under surface of the leaf, which attracts water. It is this difference in water attraction that maintains the correct orientation of the plant on the water surface. The fronds are light to medium green, often with brownish edges in mature plants, and with a distinctive fold in the center. The plant exhibits great morphological variation depending on the conditions of habitat (such as space and nutrient availability), and ranges from a slender floating specimen with leaves less than 1.5cm wide to one with leaves up to 6cm wide (Pieterse et al 2003; Kay and Hoyle 1999; Mitchell D. Pers. Comm. 2005; Agriculture & Resource Management Council of Australia & New Zealand, Australian & New Zealand Environment & Conservation Council and Forestry Ministers, 2000).
    Similar Species
    Salvinia auriculata, Salvinia biloba, Salvinia herzogii

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    Occurs in:
    lakes, water courses, wetlands
    Habitat description
    Salvinia molesta prefers tropical, sub-tropical or warm temperate areas of the world and grows best in still or slow-moving water bodies including ditches, ponds, lakes, slow rivers and canals. In standing water it forms stable floating mats. It grows optimally at a water temperature of between 20°C and 30°C. Buds are killed when exposed for more than two hours to temperatures below -3°C or above 43°C. Salvinia is able to tolerate salinity levels one tenth that of seawater, allowing the weed to adapt to a wide range of benthic environments. Its growth rate decreases by 25% at a salinity level of 0.3%. Growth is greatly stimulated by an increase in nutrient levels. As a consequence the weed is particularly fast-growing in areas where the hydrological regime has been altered by humans, encouraging an increase in nutrient levels (for example by increased runoff or fertiliser leaching) (WAPMS 2003; Mitchell D. Pers. Comm. 2005; Agriculture & Resource Management Council of Australia & New Zealand, Australian & New Zealand Environment & Conservation Council and Forestry Ministers, 2000; Howard and Harley 1998).
    General impacts
    Salvinia molesta can form dense vegetation mats that reduces water-flow and lowers light and oxygen levels in the water. This stagnant dark environment negatively affects the biodiversity and abundance of freshwater species, including fish and submerged aquatic plants. S. molesta can alter wetland ecosystems and cause wetland habitat loss. Salvinia invasion also poses a severe threat to socio-economic activities that are dependent on open, flowing and/or high quality waterbodies, including hydro-electricity generation, fishing and boat transport.
    For more details on the general impacts of this species please see general impacts of Salvinia molesta
    Uses
    Floating aquatic weeds have been used for mulch, compost, fodder, paper making, handicrafts and bio-gas generation (Howard and Harley, 1998). The main impediment to the commercial use of floating aquatic weeds such as Salvinia is their high water content, which is often up to 90% of the harvest wet weight. Thus a large proportion of the harvest is water, while only a small proportion is actually plant matter.
    The high growth rate of aquatic weeds may lead to an optimistic evaluation of their commercial use but the commerical benefits are negligable in comparison to their known wide-ranging negative socio-economic and environmental impact (Julien et al 2002; Mitchell D. Pers. Comm. 2005).
    Geographical range
    Native range: Salvinia molesta is native to southeastern Brazil and northern Argentina.
    Uncertain biostatus: Cuba, Trinidad & Tobago and Mexico are listed by some information sources as the native range of this species and in others as the known introduced range
    Known introduced range: Africa: Botswana, Burkina Faso, Côte d’Ivoire, Ghana, Kenya, Madagascar, Mauritius, Namibia, Senegal, South Africa, Swaziland, Tanzania, Uganda, Zambia; Asia: India (south), Indonesia (Kalimantan), Malaysia (Sabah, Sarawak), Philippines, Singapore, Sri Lanka, Thailand; ; North America: USA (– Arizona, California, Florida, Hawaii, Louisiana, Mississippi, North Carolina, Texas); Oceania: Australia (Australian Capital Territory, New South Wales, Queensland, Tasmania, South Australia, Victoria, Western Australia), Fiji, French Polynesia, New Caledonia, New Zealand, Papua New Guinea, Vanuatu (PIER 2012, EPPO 2012).
    Introduction pathways to new locations
    Floating vegetation/debris: Salvinia molesta reproduces vegetatively and is dispersed by wind and water (PIER 2012).
    For ornamental purposes: The attraction of Salvinia molesta as an ornamental plant and as one of particular botanical interest has led to its spread to a far greater extent through intercontinental transport in aquarium and landscaping trades. Its introduction to North America, Asia, Africa, and other continents has been linked to cultivation activities of botanical gardens and commercial horticulture sites. For example in Senegal S. molesta was first present as an ornamental plant kept in nurseries in Dakar (McFarland et al., 2003; Pieterse, pers. Obs.; in Pieterse et al, 2003).
    Nursery trade: Salvinia molesta is cultivated in public and private aquatic gardens, and nurseries in at least seventeen states in the USA. These sites are potential sources of release into natural systems and interestingly many cultivations are located in areas where infestations have been documented (McFarland et al., 2003).
    Other: It is believed that Salvinia molesta was first introduced into Sri Lanka into the Botony Department of the University of Colombo in 1943 (Williams, 1956, in Room and Fernando, 1992). Apparently a botanist at the University of Dakar (the capital of Senegal) was also responsible for encouraging the spread of the weed into the Sengal river (Pieterse et al, 2003).
    Pet/aquarium trade: Salvinia molesta is a popular aquarium plant throughout Australia (despite being banned) and continues to be kept in ponds and fish tanks in all States. It is sold through market gardens, pet shops, landscapers, with supplies coming from both wild harvesters and commercial growers. It is traded amongst home gardeners, pond owners and permaculturists (ARMCANZ, 2000).
    Ship: Floating aquatic weeds, including Salvinia molesta, may be spread on contaminated barges or log rafts (Howard and Harley, 1998).


    Local dispersal methods
    Boat: Salvinia molesta may be spread within and between water-bodies by contaminated boats, boat trailers, motors and recreation and fishing gear. The movement of boats to and from lake Kariba in Zimbabwe may have been responsible for the spread of salvinia into inland waterways (Swearingen et al., 2002; Chikwenhere and Keswani, 1997).
    Garden escape/garden waste: The plants popularity with pond and aquarium owners, its floating mechanism of dispersal and its rapid growth rate have made it an especially good candidate for garden escape. Most incursions of the weed into natural habitats in Australia are thought to be due to the cultivation of salvinia by aquarium or pond owners and its subsequent release due to floods or intentional dumping by humans into the environment (ARMCANZ, 2000).
    Off-road vehicles: Salvinia molesta may be spread over long distances (within or between waterbodies) on anything entering infested waters, including boats, trailers, vehicular wheels, engine intakes, fishing gear, recreational gear and boots (Howard and Harley, 1998; McFarland et al., 2003).
    On animals: Animals may also contribute to vegetative spread; hippos in Africa and water buffalo in Australia have been recorded to carry Salvinia molesta both within and between water-bodies (Miller and Wilson 1989, Storrs and Julien 1996, in McFarland et al., 2003; Howard and Harley, 1998).
    On animals (local): Salvinia molesta reproduces vegetatively and is dispersed by wind and water (PIER 2012).
    Water currents: Vegetative propagules of Salvinia molesta may be spread within water-bodies by water currents (Howard and Harley, 1998).
    Management information
    The optimum strategy is to prevent the introduction of Salvinia into a wetland or other water body. Legislation may restrict the import of the plant into a country. Within-country movement is more difficult to achieve and may depend on increased public awareness and education. This may be addressed by targeting stakeholders and organisations that are implicated in the spread of the weed, such as those associated with the aquarium trade.
    For details on management of this species, please see management information

    Proliferation of aquatic weeds is often indicative of increased nutrient levels in watersheds and wetlands. This may mean several species of floating aquatic weeds may be waiting to replace Salvinia. Following Salvinia removal continuous monitoring of infestation sites to detect aquatic plant succession is necessary. Sustainable management of the whole ecosystem, decreasing the nutrient level and improving sewage drainage and effluent treatment is likely to reduce the biomass of floating plants such as S. molesta (Howard and Harley 1998; Chikwenhere and Keswani 1997; Room and Fernando 1992; McFarland et al. 2003).

    Risk assessments of Salvinia molesta were carried out for Australia and Hawaii using the Australian risk assessment system (Pheloung, 1995). The result was high scores of 19 and 29 respectively and a recommendation of: reject the plant for import (Australia) or species likely to be of high risk (Pacific).

    Salvinia was added to the EPPO Alert List in 2007 and transferred to the List of Invasive Alien Plants in 2012 (EPPO 2012).
    A study was conducted in Spain aimed at identifying and ranking non-native plant species that could potentially become invasive in Spain if introduced. The Australian Weed Risk Assessment system and a Risk Assessment for Central Europe developed by Weber & Gut (2004) was used to rank a preliminary list of species. The list contained invasive plants in neighbouring countries and in other Mediterranean regions of the world but not present in Spain. The species with higher scores and therefore with the highest risk of becoming invasive in Spain if introduced, were mainly aquatic plants. Chromolaena odorata (Asteraceae) obtained the highest score in both tests, S. molesta was in the top four on both the lists (Andreu & Vila 2010)

    This section is under revision

    Reproduction
    Salvinia molesta produces egg-shaped, slender-tipped sporocarps that develop in elongated chains along the submersed fronds. Sporocarps contain numerous sporangia (which are usually empty or contain only a few deformed spore remnants). Because the plant is pentaploid (contains five sets of chromosomes) it can not produce viable spores (due to an unequal division of chromosomes during meiosis). As a consequence S. molesta is sterile and can only reproduce asexually. The plant propagates by vegetative growth and sporadic fragmentation, resulting in small vegetative propagules that are dispersed by water currents (Jacono 2003).
    Lifecycle stages
    Depending on the climate Salvinia molesta may be either a perennial or an annual. In non-tropical regions it may function as an annual but it will still produce significant growth during the summer period. In nutrient rich waters it may reach a density of 30 000 small plants per m² and under ideal growth conditions it can double its biomass in two days. The plant passes through three identifiable growth stages, the development of which are determined by environmental conditions). The growth of single ramets (plantlets) is known as the primary growth stage and the growth of a linear chain of ramets is known as the secondary growth stage. Finally, the formation of a compact vegetative cluster is known as the tertiary phase.
    This species has been nominated as among 100 of the "World's Worst" invaders
    Reviewed by: Under Revision
    Dr David Mitchell Adjunct Professor School of Environmental and Information Science Charles Sturt University Australia
    Compiled by: National Biological Information Infrastructure (NBII), Comité français de l'UICN (IUCN French Committee) & IUCN SSC Invasive Species Specialist Group (ISSG)
    Updates with support from the Overseas Territories Environmental Programme (OTEP) project XOT603, a joint project with the Cayman Islands Government - Department of Environment
    Last Modified: Monday, 4 October 2010


ISSG Landcare Research NBII IUCN University of Auckland