- Summary of Invasiveness
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Distribution Table
- Risk of Introduction
- Habitat List
- Hosts/Species Affected
- Biology and Ecology
- Latitude/Altitude Ranges
- Natural enemies
- Notes on Natural Enemies
- Means of Movement and Dispersal
- Impact Summary
- Economic Impact
- Environmental Impact
- Social Impact
- Risk and Impact Factors
- Detection and Inspection
- Similarities to Other Species/Conditions
- Prevention and Control
- Gaps in Knowledge/Research Needs
- Links to Websites
- Distribution Maps
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IdentityTop of page
Preferred Scientific Name
- Salvinia minima Baker (1886)
Other Scientific Names
- Salvinia auriculata Aublet
- Salvinia rotundifolia
International Common Names
- English: aquarium watermoss; butterfly fern; common salvinia; eared watermoss; floating fern; floating moss; salvinia; water fern; water salvinia; water spangles
Local Common Names
- Germany: schwimmfarne
Summary of InvasivenessTop of page
S. minima is a very productive free-floating, non-rooted aquatic fern native to South and Central America. It was introduced outside its native range in southern Florida, USA in 1926 (USGS, 2005). The plant is degrading wetland ecosystems in several states of the USA (Tipping and Center, 2005). S. minima has an extremely high reproductive potential; the plants can rapidly colonize bodies of water, forming thick mats that displace native species, impact water quality, impede recreational activities, and clog waterways and irrigation channels (Rayachhetry et al., 2002). S. minima is also resistant to desiccation, allowing it to be transported long distances out of water (ISSG, 2006). The species can act as an annual, dying back when temperatures decrease and causing harmful nutrient pulses and dissolved oxygen crashes (Dickinson and Miller, 1998).
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Plantae
- Phylum: Pteridophyta
- Class: Filicopsida
- Order: Hydropteridales
- Family: Salviniaceae
- Genus: Salvinia
- Species: Salvinia minima
Notes on Taxonomy and NomenclatureTop of page
The heterosporous fern clade, of which Salvinia minima is a part, contains two families, Marsileaceae and Salviniaceae. These water ferns are the only group of heterosporous plants to have evolved heterospory after the Paleozoic. The group evolved and then diversified at the same time as flowering plants (Nagalingum et al., 2006). The family Salviniaceae is monogeneric, and includes ten species of Salvinia, all of which are highly morphologically similar (Jacono et al., 2001; USDA-NRCS, 2008). The names Salvinia auriculata Aublet, Salvinia natans (Linnaeus) Allioni and Salvinia rotundifolia Willdenow have been misapplied to Salvinia minima in several sources, and S. auriculata is occasionally erroneously listed as synonymous (Flora of North America Editorial Committee, 1994).
DescriptionTop of page
S. minima is a deep-green, free-floating, rootless, aquatic fern (ISSG, 2006). Stems can be up to 6 cm and leaves are from 1-1.5 cm long and almost round to elliptic. They are obtuse or notched at the apex and round to heart-shaped at the base. The upward surfaces of the fronds are covered with stiff hairs, with four separated branches. The under surface of the leaves are brown and pubescent with slender and unbranched hairs (Flora of North America Editorial Committee, 1993). The stiff hairs on the fronds serve to trap air, thus providing buoyancy (Dickinson and Miller, 1998). Obscure veins are areolate and do not quite reach to the leaf edges. Sporocarps occur in groups of four to eight, with up to 25 megasporangia (Flora of North America Editorial Committee, 1993).
DistributionTop of page
S. minima occurs in lakes, riparian zones, water courses, wetlands and pools (ISSG, 2006) in warm temperate areas (Jacono et al., 2001). The species is common and wide-ranging from southern Mexico to northern Argentina and Brazil; however, the natural range in Argentina cannot be accurately determined due to the frequency of use in the water-garden and aquarium trade (USGS, 2005). The species is native to South America, but is now established in the southern states of the USA (Tipping and Center, 2005). These aquatic ferns have invaded drainage basins in Texas, Louisiana, Alabama, Arizona, California, Florida, Georgia, Hawaii, Mississippi, North Carolina and Oklahoma (Rayachhetry et al., 2002). The species grows best in slow-moving or still water and can tolerate salinity levels up to 7 ppt (ISSG, 2006).
Distribution TableTop of page
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
IntroductionsTop of page
Risk of IntroductionTop of page
People commonly grow S. minima speciesin aquaria and water-gardens. Consequently, the plant has been distributed through related activities (Haynes and Jacono, 2000). S. minima is still readily available in the aquaculture industry for direct purchase or can be included as a hitchhiker (ISSG, 2006). The species spreads not only clonally, but also by spores, therefore ship ballast water that contains spores can spread the plant internationally (ISSG, 2006). The earliest collection in North America was made around 1930 and was likely to be the result of ballast discharge of contaminated water in the St. Johns River near Jacksonville (ISSG, 2006). Plants were then documented in wide ranging locations across Florida and Georgia, which were likely to be the result of independent introductions (Jacono et al., 2001).
HabitatTop of page
S. minima occurs in still or slow-moving water in tropical and warm temperate area of North and South America (Tipping and Center, 2005). It prefers the shallow backwaters in bayous, lakes and ponds, low-energy streams, oxbows, ditches, swamps and marshes (USGS, 2005). It occurs frequently in waters with high organic content (University of Florida, 2002), and typically inhabits water bodies with salinity levels as high as 4-7ppt (USGS, 2005). S. minima, due to its interesting morphology, is a popular aquarium and water-garden plant, it can grow fairly well in small, artificially constructed ponds (USACE-ERDC, 2002).
Habitat ListTop of page
|Irrigation channels||Principal habitat||Harmful (pest or invasive)|
|Irrigation channels||Principal habitat||Productive/non-natural|
|Lakes||Principal habitat||Harmful (pest or invasive)|
|Reservoirs||Principal habitat||Harmful (pest or invasive)|
|Rivers / streams||Secondary/tolerated habitat||Harmful (pest or invasive)|
|Rivers / streams||Secondary/tolerated habitat||Productive/non-natural|
|Ponds||Principal habitat||Harmful (pest or invasive)|
Hosts/Species AffectedTop of page
S. minima is a highly competitive species with a very high growth rate. Colonies of S. minima can grow very densely, such that they shade light from valuable native submerged aquatic plant species (USACE-ERDC, 2002). Dense colonies can thus decrease local biodiversity and degrade the habitat (ISSG, 2006). The plant is also highly competitive among other free-floating species. A competition study specifically showed that S. minima had negative effects on the change in cover of the species Azolla caroliniana and Spirodela punctata (Dickinson and Miller, 1998). In Louisiana, USA native Lemna species were completely replaced by S. minima (ISSG, 2005).
Biology and EcologyTop of page
The taxonomy of the genus Salvinia is relatively straightforward. The genus contains approximately 10 closely related species in the monogeneric family Salviniaceae. De la Sota and Cassa de Pazos (2001) report that the species S. minima has two distinct cytotypes: 2n=4x=36 and 2n=6x=54. The first population occurred in Brazil, and the second in Argentina. In its adventive range, genetic distances range to .48, which are high for an introduced, vegetatively reproducing plant (Madeira et al., 2003).
S. minima reproduces vegetatively. Branching and fragmentation of rhizomes leads to the production of a high number of daughter plants (USGS, 2005) The stiff hairs on the surface of the leaf help to slow the desiccation of the plant, thus allowing it to spread long distances out of water (USGS, 2005). Members of the genus occasionally reproduce via spores produced in sporocarps (USACE-ERDC, 2002), but fertile specimens are so rarely reported that the species is essentially considered sterile (Flora of North America Editorial Committee, 1993).
Physiology and Phenology
High rates of vegetative reproduction occur throughout the growing season. Lateral buds are found deeply imbedded in the stem, and will also lie dormant during dry and cold periods, sprouting when warmer temperatures occur. Additionally, rhizome fragments can also lie dormant in vegetation until favourable growing conditions return (ISSG, 2006). Dickinson and Miller (1998) showed that the competitive effects of S. minima varied with the seasons, the plant took over the surface area during the summer, but grew only very slowly in the autumn, when its competitive effects were minimal.
Few reports of this species’ associates and the corresponding strength of those associations exist in the literature. One field study on the competitive ability of floating-leaf species, reports S. minima from a habitat that also supports the other floating-leaf species Azolla caroliniana, Spirodella punctata, Wolffia spp., Wolffiella spp. and Lemna spp. This same habitat also supports Typha, Sparganium americanum, Hydrocotyle ranunculoides, Myriophyllum spp. and Bidens laevis (Dickinson and Miller, 1998).
S. minima can grow in a wide variety of aquatic habitats, but does best in those with a high organic content (University of Florida, 2002). It is also most frequently found in still and slow-moving water. Phytoremediation investigations suggest that S. minima be grown at a pH of 5.0 or 6.0 and with a maximum initial ammonium-nitrogen concentration of 70 mg/L (Olguin et al., 2007). The species is sensitive to high salinity; coastal populations in Texas, USA are sometimes only found during the winter months, when salinity decreases to approximately 4-7 ppt (USGS, 2005).
ClimateTop of page
|C - Temperate/Mesothermal climate||Tolerated||Average temp. of coldest month > 0°C and < 18°C, mean warmest month > 10°C|
|Cf - Warm temperate climate, wet all year||Tolerated||Warm average temp. > 10°C, Cold average temp. > 0°C, wet all year|
|Cs - Warm temperate climate with dry summer||Tolerated||Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers|
|Cw - Warm temperate climate with dry winter||Tolerated||Warm temperate climate with dry winter (Warm average temp. > 10°C, Cold average temp. > 0°C, dry winters)|
Latitude/Altitude RangesTop of page
|Latitude North (°N)||Latitude South (°S)||Altitude Lower (m)||Altitude Upper (m)|
Natural enemiesTop of page
Notes on Natural EnemiesTop of page
Several herbivorous insects are reported from field surveys. The semi-aquatic grasshopper Paulinia acuminata oviposits on S. minima fronds and has shown promise in the biological control of S. molesta (Julien et al., 2002). The curculionid Neohydronomus affinis, which occurs naturally as a predator of water lettuce, will also feed and oviposit on S. minima. A weevil species (Cyrtobagous salviniae) similarly uses populations of S. minima for food and during reproduction (Tipping and Center, 2005). In fact, the weevil is found widely in Florida, USA but in no other states in S. minima’s adventive range, which may explain the higher nuisance levels reported from other states (Jacono et al., 2001).
Means of Movement and DispersalTop of page
S. minima spreads vegetatively, and due to its resistance to desiccation provided by the stiff leaf hairs, it can hitchhike between waterbodies over long distances on boats, trailers, alligators, turtles and dogs (USGS, 2005). The free-floating plant may also spread passively with water movement.
The discharge of ship ballast water contaminated with spores may explain the initial introduction of S. minima outside its native range (ISSG, 2006). However, because the plant is largely sterile, the spread of spores may prove less of a threat than vegetative spread. The plant is free-floating, and highly capable of passive transmission, although its resistance to desiccation means it is easily transported on boating and other recreational equipment, humans and wildlife.
People report seeing S. minima transported on boats, trailers, and dogs. The ability of this plant to act as a hitchhiker makes it an excellent candidate for accidental introduction (ISSG. 2006). It is also occasionally included as a contaminant in aquaculture mailings (ISSG, 2006).
S. minima is an important plant in the water-garden industry. It is widely available for purchase, and people may intentionally plant the species in areas where it may escape to natural environments (ISSG, 2006).
Impact SummaryTop of page
|Cultural/amenity||Positive and negative|
|Economic/livelihood||Positive and negative|
|Human health||Positive and negative|
Economic ImpactTop of page
This species is capable of an extremely high growth rate. In its adventive range the plants can rapidly colonize bodies of water, forming thick mats that displace native species, impact water quality, impede recreational activities, clog waterways, water intakes and irrigation channels, it can also interfere with power generation, and decrease the integrity of fisheries (Rayachhetry et al., 2002; USGS, 2005). All of these factors present some economic impacts that can be severe, although specific studies that quantify the economic damage are lacking.
Environmental ImpactTop of page
Impact on Habitat
The introduction of S. minima poses a significant threat to aquatic systems in the southern areas of the USA (Jacono et al., 2001). This species is highly productive during the summer, but quickly dies back as soon as temperatures decrease (Dickinson and Miller, 1998). The sudden pulse of decaying organic matter can cause nutrient pulses and dissolved oxygen crashes that can result in fish-kills and algae blooms. Mats can occur as thick as 25 cm and cause significant light attenuation, shading submersed plants beneath the mats (ISSG, 2006). S. minima is extremely competitive and can displace native vegetation and result in a decrease in food and habitat available for other native organisms (ISSG, 2006).
Impact on Biodiversity
S. minima can outcompete native plant species (ISSG, 2006), this likely corresponds to a decrease in local biodiversity, although specific studies that measure this impact have yet to be conducted.
Social ImpactTop of page
This plant can cause substantial nuisance to recreational users by impeding navigation and tangling fishing lines. S. minima is capable of extremely dense growth, creating mats as thick as 20 to 25 cm (USGS, 2005). This species can reduce swimming access, founder livestock, and stimulate unsightly, possibly toxic, algal blooms. In Louisiana, USA the plants occur in a thick mat almost entirely covering a waterway with an area 19.3 km x 110 m. These thick mats clog waterways, irrigation channels, affect power generation and block water intakes (USGS, 2005).
Risk and Impact FactorsTop of page Invasiveness
- Proved invasive outside its native range
- Abundant in its native range
- Highly adaptable to different environments
- Tolerant of shade
- Benefits from human association (i.e. it is a human commensal)
- Fast growing
- Has high reproductive potential
- Reproduces asexually
- Damaged ecosystem services
- Ecosystem change/ habitat alteration
- Infrastructure damage
- Modification of hydrology
- Modification of natural benthic communities
- Modification of nutrient regime
- Monoculture formation
- Negatively impacts cultural/traditional practices
- Negatively impacts livelihoods
- Negatively impacts aquaculture/fisheries
- Negatively impacts tourism
- Reduced amenity values
- Reduced native biodiversity
- Threat to/ loss of native species
- Transportation disruption
- Competition - monopolizing resources
- Competition - shading
- Rapid growth
- Highly likely to be transported internationally accidentally
- Highly likely to be transported internationally deliberately
UsesTop of page
S. minima has successfully been used in water reclamation activities. It has been used quite often in the treatment of water contaminated with lead and cadmium, as well as for treating high-strength synthetic organic wastewater (Outridge and Hutchinson, 1991; Olguin et al., 2005; Olguin et al., 2007).
S. minima has been used industrially in the phytoremediation of water contaminated with heavy metals and organic waste (Outridge and Hutchinson, 1991; Olguin et al., 2005; Olguin et al., 2007).
Detection and InspectionTop of page
S . minima is free-floating, which makes it easier to identify than most submerged aquatic vegetation. Volunteer monitors should be trained on the identity and habit of this potential invader.
Similarities to Other Species/ConditionsTop of page
All Salvinia species have stems with many multicellular hairs, leaves are horizontally spreading; floating leaves are green and pubescent. Sporocarps are borne on structures resembling cymes or on submerged leaves. Although the species resemble each other quite significantly, they can be distinguished from other floating leaf species by the unique upper side of the floating leaf (Flora of North America Editorial Committee, 1993). Distinguishing among the various species in the Salvinia genus is difficult, and requires recognizing the differences in spore placement and leaf shape (USGS, 2005). It is, however, distinct from the very important S. molesta and others in the S. auriculata complex in that the papillae on the upper suface of the fronds have free branches, rather than being closed in a 'bird-cage' form.
Prevention and ControlTop of page
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
The vegetative propagules of this species are very easy to spread. Therefore, educational programmes are usually necessary to decrease this form of human-mediated spread. Teaching users how to clean equipment in a way that decreases the chance of transmission is one way to lessen the impact of the human vector. Several of the USA states have legislated the regulation of the purchase, transportation, and introduction of this species.
Several reports of eradication exist in the literature. If a population is removed relatively quickly, it may be possible to prevent population establishment.
Numerous educational campaigns have been directed at informing the public about the danger of aquatic invasive species, states in which S. minima is particularly problematic commonly distribute informational materials about its identity as well as how to report new invasions. Other educational campaigns have been directed toward informing the public about how to clean equipment in order to prevent the movement of invasive species.
Cultural control and sanitary measures
Fragments, ramets, rhizomes and plants are easily transportable and are resistant to desiccation. Thus, it is extremely important to decrease the instances of accidental introduction by addressing humans as a vector. By establishing guidelines on how to properly clean equipment, dispose of water, and identify target plants, it is likely that instances of accidental transportation and release will be fewer.
Mechanical harvesting may be used to control small populations of S. minima. Otherwise, as the plant is intolerant of salinity levels above 7 ppt, salt water from the Gulf is often allowed to flow into bayous along coastal sites in North America. Water drawdown to a level at which stranded plants will dry out and freeze provides effective control and nuisance relief (USGS, 2005).
Barriers, screens and booms have shown some ability to control the spread of local populations, but require significant maintenance and clearing to be truly effective (ISSG, 2006). Plants can spread via fragments, therefore much attention has been given to decreasing human-mediated dispersal. The plant is on a number of state noxious lists. Some states have put in place legislation to regulate the sale, transportation and introduction of S. minima.
The weevil Cyrtobagous salviniae has proven to be an effective natural predator in, as well as outside of, the native range of S. minima. In the USA, the weevil is found abundantly in Florida, where the species is less of a nuisance compared to the areas to which the weevil has not been introduced (Madeira et al., 2003). Of the currently explored species, the weevil shows the most promise as a biological control agent, as no barriers seem to exist barring the introduction of the weevil beyond Florida (Madeira et al., 2003).
Glyphosate and trifluralin were both highly lethal to S. minima (although triflurin is a known human health hazard), and 2,4-D significantly inhibited growth (Banzatto and Santos, 1998).
Gaps in Knowledge/Research NeedsTop of page
More research is needed to evaluate the range in impacts the species has on natives, as well as to further evaluate the impacts of the nutrient release during the winter.
ReferencesTop of page
Jacono CC; Davern TR; Center TD, 2001. The adventive status of Salvinia minima and S. molesta in the Southern United States and the related destribution of the weevil Cyrtobagous salviniae. Castanea, 66(3):214-226.
Madeira PT; Jacono CC; Tipping P; Van TK; Center TD, 2003. A genetic survey of Salvinia minima in the southern United States. Aquatic Botany, 76(2):127-139. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T4F-48CFS6T-1&_user=10&_handle=W-WA-A-A-Y-MsSAYWW-UUA-AUDVCDDYZZ-AEVDBYEDC-Y-U&_fmt=summary&_coverDate=06%2F30%2F2003&_rdoc=4&_orig=browse&_srch=%23toc%234973%232003%23999239997%23430721!&_cdi=4973&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=1c033da50aa67765daa93b8d7b22d984
Nagalingum NS; Schneider H; Pryer KM, 2006. Comparative morphology of reproductive structures in heterosporous water ferns and a reevaluation of the sporocarp. International Journal of Plant Sciences, 167(4):805-815. http://www.journals.uchicago.edu/IJPS/journal/
Olguín EJ; Sánchez-Galván G; Pérez-Pérez T, 2007. Assessment of the phytoremediation potential of Salvinia minima baker compared to Spirodela polyrrhiza in high-strength organic wastewater. Water, Air, and Soil Pollution, 181(1/4):135-147. http://springerlink.metapress.com/link.asp?id=100344
Olguín EJ; Sánchez-Galván G; Pérez-Pérez T; Pérez-Orozco A, 2005. Surface adsorption, intracellular accumulation and compartmentalization of Pb(II) in batch-operated lagoons with Salvinia minima as affected by environmental conditions, EDTA and nutrients. Journal of Industrial Microbiology & Biotechnology, 32(11/12):577-586. http://www.springerlink.com/link.asp?id=100967
Rayachhetry MB; Center TR; Center TD; Tipping P; Pratt PD; Van TK, 2002. First report of the pathogenicity of Rhizoctonia solani on Salvinia molesta and S. minima in Florida. Plant Disease, 86(7):813.
Thompson CR; Habeck DH, 1989. Host specificity and biology of the weevil Neohydronomus affinis (Coleoptera: Curculionidae), a biological control agent of Pistia stratiotes. Entomophaga, 34(3):299-306.
ContributorsTop of page
01/07/08 Original text by:
Alison Mikulyuk, Wisconsin Dept of Natural Resources, Science Operations Center, 2801 Progress Rd, Madison, WI 53716, USA
Michelle Nault, Wisconsin Department of Natural Resources, 2801 Progress Rd, Madison, WI 53716-3339, USA
Distribution MapsTop of page
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