The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

Salvinia molesta
Salvinia molesta
(giant salvinia)

Copyright Info
Salvinia molesta Mitchell

Common name: giant salvinia

Synonyms and Other Names: Kariba weed, African pyle, aquarium watermoss, koi kandy, giant salvinia, aquarium watermoss, Australian azolla, waterfern, water spangles, giant azolla

Taxonomy: available through www.itis.govITIS logo

Noxious: This species is listed by the U.S. Department of Agriculture as a noxious weed.

Identification: Free floating, aquatic fern. Consists of horizontal stems that float just below the water surface, and produce a whorl of three leaves (technically fronds) at each node. The upper pair of floating or emergent leaves are green in color and ovate to oblong in shape. The lower submerged leaf is brown, highly divided and resembles and functions as a root. The lower leaves may grow to great lengths (up to 25 cm), and by creating drag, act to stabilize the plant (Mitchell and Tur 1975; Room 1983).

Upper surfaces of green fronds are covered with rows of white, bristly hairs (papillae) (Mitchell 1972), which divide into four thin branches that soon rejoin at the tips to form a cage. The resulting structures resemble tiny eggbeaters. This characteristic eggbeater structure can reliably distinguish S. molesta from the morphologically similar S. minima that has unjoined hairs (Wunderlin and Hansen 2011). These specialized hairs create a water repellent, protective covering (Mitchell and Thomas 1972).

Salvinia molesta belongs to a group of closely related Neotropical species that share the feature of eggbeater type hairs (Mitchell 1972; Mitchell 1979). Named the “Salvinia auriculata complex”, the members include S. auriculata Aublet, S. biloba Raddi, S. herzogii de la Sota, and S. molesta. Although subtle differences have been found among the members of the group, sporocarps are generally needed to tell these species apart (Forno 1983; Mitchell 1972).

Sporocarps develop in elongated chains among the submersed leaves. Salvinia molesta is known for its egg-shaped sporocarps that end in a slender point. Mature plants can produce large quantities of sporocarps, which are actually outer sacs that contain numerous sporangia. However, the sporangial sacs are usually empty of microscopic spores or with only a few deformed remnants. Being a pentaploid species, S. molesta demonstrates irregularities during meiosis that prevent spore formation and result in functionally sterile plants (Loyal and Grewal 1966; Mitchell 1979).

Three growth forms have been described where individual leaves can range from a few millimeters to 4 centimeters in length. During early colonization small leafed, thin plants lie flat on the water surface. As populations expand, leaves curl at the edges in response to self-competition. Later a vertical leaf position is attained as mature plants press into tight chains to form mats of innumerable floating plants (Mitchell and Thomas 1972; Mitchell and Tur 1975).

Size: Paired fronds or leaves 2-4 cm long and 1-6 cm wide

Native Range: southeast Brazil (Forno 1983)

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Nonindigenous Occurrences:

Table 1. States with nonindigenous occurrences, the earliest and latest observations in each state, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Salvinia molesta are found here.

StateFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
AL1999202416Apalachicola Basin; Black Warrior-Tombigbee; Escatawpa; Lower Black Warrior; Lower Tallapoosa; Middle Chattahoochee-Walter F; Middle Tennessee-Elk; Middle Tombigbee-Chickasaw; Middle Tombigbee-Lubbub; Mississippi Coastal; Mobile Bay; Mobile-Tensaw; Mobile-Tombigbee; Pickwick Lake; Upper Alabama; Wheeler Lake
AZ199920233Imperial Reservoir; Lower Colorado; Yuma Desert
AR200820214Bodcau Bayou; Loggy Bayou; Lower Arkansas-Maumelle; Lower Sulpher
CA199920229Big-Navarro-Garcia; Central Coastal; Imperial Reservoir; Lower Colorado; Salinas; Salton Sea; San Diego; San Luis Rey-Escondido; Santa Margarita
DC200020001Middle Potomac-Anacostia-Occoquan
FL1999202312Aucilla; Big Cypress Swamp; Florida Southeast Coast; Hillsborough; Kissimmee; Lower Ochlockonee; Lower St. Johns; Myakka; Oklawaha; Pensacola Bay; St. Andrew-St. Joseph Bays; Withlacoochee
GA199920153Canoochee; Lower Ogeechee; Upper Ocmulgee
HI199920233Hawaii; Kauai; Oahu
LA1998202432Atchafalaya; Bayou D'Arbonne; Bayou Pierre; Bayou Teche; Boeuf; Caddo Lake; Castor; Cross Bayou; East Central Louisiana Coastal; Eastern Louisiana Coastal; Lake Maurepas; Liberty Bayou-Tchefuncta; Little; Loggy Bayou; Lower Calcasieu; Lower Grand; Lower Ouachita; Lower Pearl; Lower Red; Lower Red-Lake Iatt; Lower Sabine; Mermentau; Middle Red-Coushatta; Red Chute; Sabine Lake; Saline Bayou; Tangipahoa; Toledo Bend Reservoir; Upper Calcasieu; Vermilion; West Central Louisiana Coastal; West Fork Calcasieu
MS1999202314Black; Buffalo; Escatawpa; Homochitto; Lower Leaf; Lower Pearl; Middle Pearl-Strong; Mississippi Coastal; Pascagoula; Pickwick Lake; Sucarnoochee; Tibbee; Upper Leaf; Upper Tombigbee
NC200020216Black; Lower Cape Fear; Lumber; New River; Northeast Cape Fear; White Oak River
PR200020244Cibuco-Guajataca; Culebrinas-Guanajibo; Eastern Puerto Rico; Puerto Rican Eastern Islands
SC199520237Broad-St. Helena; Calibogue Sound-Wright River; Carolina Coastal-Sampit; Cooper; Lake Marion; Lower Savannah; Salkehatchie
TX1998202437Buffalo-San Jacinto; Caddo Lake; East Fork San Jacinto; East Galveston Bay; Elm Fork Trinity; International Falcon Reservoir; Lake Fork; Lake O'the Pines; Lampasas; Lower Angelina; Lower Brazos; Lower Brazos-Little Brazos; Lower Colorado; Lower Neches; Lower Sabine; Lower Sulpher; Lower Trinity; Lower Trinity-Kickapoo; Lower Trinity-Tehuacana; McKinney-Posten Bayous; Middle Sabine; Navasota; Navidad; Neches; North Galveston Bay; Pine Island Bayou; Sabine Lake; San Bernard; South Corpus Christi Bay; Spring; Toledo Bend Reservoir; Upper Angelina; Upper Neches; Upper Trinity; West Fork San Jacinto; West Galveston Bay; Wichita
VI201220121St. Croix
VA200420041North Fork Shenandoah

Table last updated 6/24/2024

† Populations may not be currently present.

Ecology: Reproduction is strictly vegetative as spores are sterile (Mitchell 1979). Under favorable natural conditions, biomass can double in about one week to 10 days (Mitchell and Tur 1975; Mitchell 1979).  Biomass weights of live plants approach those recorded for floating waterhyacinth (Eichhornia crassipes (Mart.) Solms) (Mitchell 1979).

Salvinia molesta demonstrates tolerance to freezing air temperature, but cannot withstand ice formation on the water surface except when dense mats protect the underlying plants (Whiteman and Room 1991).

Salvinia molesta is strictly a freshwater species, not tolerating brackish or marine environments.  In experimental trials, salinity above 7 parts per thousand (ppt) slowed growth and damaged plant tissues.  Higher salt concentrations proved lethal.  Plants maintained at 11 ppt were killed after 20 hours exposure.  Full strength seawater (35 ppt) killed plants in 30 minutes (Divakaran et al. 1980).

Means of Introduction: The first establishment outside of its native range was in Sri Lanka in 1939 (Room 1990), by the Botany Department at the University of Colombo.  The species continued to be introduced to other warm regions of the world intentionally as an aquarium and water garden plant, and unintentionally as a contaminant in shipments of other aquatic plants (Oliver 1993; Nelson 1984).  Once established in a new region, the plant is likely spread as a hitchhiker on boats, trailers and other recreational gear.  Local movement between waterbodies may be facilitated by birds and aquatic mammals (Mitchell and Thomas 1972).

Spread will continue through natural drainage and flow in river and stream systems. In lakes and large water-bodies upright well buoyed leaves are effectively dispersed by wind and currents to infest new coves.

Status: Populations established in the southeast and southwest U.S., including Guam, Hawaii, and Puerto Rico. Extirpated from colder climate states (Connecticut, District of Columbia, Kansas, Missouri, Virginia) and eradicated from Northern Alabama and California, and parts of the Carolinas, Florida, and Texas. More than 99% of the Pascagoula River population was killed by storm surge salinity or by being deposited on land during Hurricane Katrina in 2005, thus leaving about 2 hectares of S. molesta distributed over ~20 sites (Fuller et al. 2010).

Impact of Introduction:
Summary of species impacts derived from literature review. Click on an icon to find out more...

EcologicalEconomicHuman Health

Salvinia molesta has the potential to alter aquatic ecosystems in several ways.  Rapidly expanding populations can overgrow and replace native plants resulting in dense surface cover that prevents light and atmospheric oxygen from entering the water.  Decomposing plant material drops to the bottom, consuming dissolved oxygen needed by fish and other aquatic life (Divakaran et al. 1980).  Flores and Carlson (2006) noted a 2.5 fold increase in dissolved oxygen by removing 90% of S. molesta at five east Texas sites.

Floating mats of S. molesta can be up to one meter thick (Whiteman and Room 1991), impeding navigation, reducing water flow and interfering with fishing and recreational activities (Mitchell and Thomas 1972).  This could be significant in areas where economic or subsistence fishing is important (Mitchell et al. 1980).  Like dense floating mats of waterhyacinth, dense floating mats of S. molesta support secondary colonizing plants, leading to the formation of floating islands or tussocks (McFarland et al. 2004; Mitchell et al. 1980).

Few have researched the beneficial effects of S. molesta. Due to its floating habit, S. molesta was utilized to treat sewage and industrial effluent (Finlayson et al. 1982). Asian countries have supplemented livestock fodder with S. molesta, and utilized it as a compost and mulch (Oliver 1993; Thomas and Room 1986).

References: (click for full references)

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Bister, T.J., and M.W. Brice. 2008a. Brandy Branch Reservoir 2007 Survey Report. Texas Parks and Wildlife Department, Austin, TX. http://www.tpwd.state.tx.us/publications/pwdpubs/lake_survey/pwd_rp_t3200_1253/index.phtml.

Bister, T.J., and M.W. Brice. 2008b. Lake Pinkston 2007 Survey Report. Texas Parks and Wildlife Department, Austin, TX. http://www.tpwd.state.tx.us/publications/pwdpubs/lake_survey/pwd_rp_t3200_1360/.

Brown, L.E., G. Nesom, S.J. Marcus, and D. Rosen. 2009. Plants of Trinity River National Wildlife Refuge. Trinity River NWR, US Fish and Wildlife Services, Liberty, TX. http://www.fws.gov/uploadedFiles/TRNWRPlants_2009.pdf.Calflora. 2015. Berkeley, California: The Calflora Database. http://www.calflora.org/. Accessed on 12/04/2015.

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Caudales, R., E.V. Hernandez, A. Sanchez-Perez, and H.L. Liogier. 2000. Aquatic and wetland plants of Puerto Rico. I. Pteridophyta. Anales Jardin Botanico de Madrid 57(2).

Center for Invasive Species and Ecosystem Health. 2015. EDDMapS: Early detection and distribution mapping system. The University of Georgia, Tifton, GA. http://www.eddmaps.org.

Consortium of California Herbaria. 2014. Consortium of California Herbaria. Consortium of California Herbaria, Berkeley, CA.

Divakaran, O., M. Arunachalam, and N. Balakrishnan Nair. 1980. Growth rates of Salvinia molesta Mitchell with special reference to salinity. Proceedings of the Indian Academy of Sciences, Plant Sciences 89(3):161-168.

Finlayson, C.M., T.P. Farrell, and D.J. Griffiths. 1982. Treatment of sewage effluent using the water fern salvinia. Water Research Foundation of Australia, Kingsford, New South Wales.

Flores, D. and J.W. Carlson. 2006. Biological control of giant salvinia in east Texas waterways and the impact on dissolved oxygen levels. Journal of Aquatic Plant Management 44:115-121.

Forno, I.W. 1983. Native distribution of the Salvinia auriculata complex and keys to species identification. Aquatic Botany 17:71-83.

Fuller, P.L., M.G. Pursley, D. Diaz, and W. Devers. 2010. Effects of Hurricane Katrina on an incipient population of giant salvinia Salvinia molesta in the lower Pascagoula River, Mississippi. Gulf and Caribbean Research 22:63-66.

Giant salvinia Task Force. 2002. Lower Colorado River Giant Salvinia Task Force Action Plan. Lower Colorado River Giant Salvinia Task Force. http://www.anstaskforce.gov/Species%20plans/Giant%20Salvinia.pdf (accessed on November 12, 2006).

Heidgerd, D. 2015. Pesky invasive plant turns up in another east Texas waterway. NBCDFW.com. Fort Worth, TX. http://www.nbcdfw.com/news/local/Pesky-Invasive-Plant-Turns-Up-in-Another-East-Texas-Waterway-353166401.html. Created on 11/24/2015. Accessed on 11/24/2015.

Johnson, D. 1995. Giant salvinia found in South Carolina. Aquatics 17(4):22. http://www.fapms.org/aquatics/issues/1995winter.pdf.

Johnson, N.O. 2008. State to get tough to protect Caddo, other waterways. The Longview News-Journal, Longview, TX. 2008 (April 9). http://www.news-journal.com/news/content/news/stories/2008/04/09/04092008_lake_vegetation.html (accessed on 14 April 2008).

Knight, S. 2008. Unwanted plant's impact swift. Tyler Morning Telegraph, TylerPaper.com, Tyler, TX. 2008 (February 14). http://www.tylerpaper.com/article/20080214/SPORTS0202/802130364.

Louisiana Department of Wildlife and Fisheries, Inland Fish Division. 2013. Turkey Creek Lake vegetation control plan. Louisiana Department of Wildlife and Fisheries, Baton Rouge, LA. http://www.wlf.louisiana.gov/sites/default/files/pdf/document/37764-aquatic-vegetation-control-plans/turkey_creek_avcp_2013_0.pdf

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Loyal, D.S. and R.K. Grewal. 1966. Cytological study on sterility in Salvinia auriculata Aublet with a bearing on its reproductive mechanism. Cytologia 31(3):330-338.

Lund University. 2010. Lund Botanical Museum. Lund University, Lund, Sweden.

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McFarland, D.G., L.S. Nelson, M.J. Grodowitz, R.M. Smart, and C.S. Owens. 2004. Salvinia molesta D. S. Mitchell (giant salvinia) in the United States: a review of species ecology and approaches to management. U.S. Army Corps of Engineers, Engineer Research and Development Center, Vicksburg, MS. http://el.erdc.usace.army.mil/elpubs/pdf/srel04-2.pdf.

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Author: Thayer, D.D., I.A. Pfingsten, C.C. Jacono, M.M. Richerson, and V. Howard

Revision Date: 8/27/2018

Peer Review Date: 2/8/2016

Citation Information:
Thayer, D.D., I.A. Pfingsten, C.C. Jacono, M.M. Richerson, and V. Howard, 2024, Salvinia molesta Mitchell: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/FactSheet.aspx?SpeciesID=298, Revision Date: 8/27/2018, Peer Review Date: 2/8/2016, Access Date: 6/24/2024

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.


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Citation information: U.S. Geological Survey. [2024]. Nonindigenous Aquatic Species Database. Gainesville, Florida. Accessed [6/24/2024].

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