Salvinia molesta
Salvinia molesta
(giant salvinia)
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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

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)

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Puerto Rico &
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Guam Saipan
Interactive maps: Point Distribution Maps

Nonindigenous Occurrences: Salvinia molesta has been recorded in the U.S. outside of cultivation since 1995, where it was discovered in a small pond in Colleton County, South Carolina (Johnson 1995; Whetstone et al. 1999).

  • Alabama - Lower Tallapoosa, Middle Chattahoochee-Walter F (University of Alabama Biodiversity and Systematics 2007), and Middle Chattahoochee-Walter F George Reservoir (Mike Eubanks, USACE, pers. comm.) drainages, and Blount, Cullman, Lawrence, Lee, Russell, and Shelby Counties (National Agricultural Pest Information System 2007)
  • Arizona - Imperial Reservoir, Lower Colorado, Lower Gila, and Yuma Desert (Center for Invasive Species and Ecosystem Health 2015) drainages
  • Arkansas - Little Maumelle River, downstream from the Pinnacle Mountain State Park of Lower Arkansas-Maumelle drainage, McKinney Bayou of the Red River in the Sulphur [River] Bottoms of Lower Sulpher drainage (Peck 2011)
  • California - Big-Navarro-Garcia (California Department of Food and Agriculture 2004), Central Coastal, Newport Bay, Salinas, Salton Sea, Santa Ana, Seal Beach (Consortium of California Herbaria 2014), Imperial Reservoir (Giant salvinia Task Force 2002), Lower Colorado (Center for Invasive Species and Ecosystem Health 2015), Lower Sacramento (Calflora 2015), San Diego, and Santa Margarita (Consortium of California Herbaria 2014) drainages
  • Florida - Big Cypress Swamp (University of Florida Herbarium 2016), Hillsborough, St. Andrew-St. Joseph Bays (Center for Invasive Species and Ecosystem Health 2015), Lower Ochlockonee (Jess Van Dyke, FL DEP, pers. comm.), and Oklawaha (Robert Kipker, FL DEP, pers. comm.) drainages
  • Georgia - Canoochee (University of Alabama Biodiversity and Systematics 2007), Lower Ogeechee (University of Florida Herbarium 2016), and Upper Ocmulgee (New York Botanical Garden 2015) drainages
  • Hawaii - Waiakea Pond (also known as Waidkea Pond) in Hilo of Hawaii drainage (Mindy Wilkinson, HI DLNR, pers. comm.), and private taro farms of Oahu drainage (Bernice Pauahi Bishop Museum 2015)
  • Louisiana - Atchafalaya, Bayou Pierre, West Central Louisiana Coastal (Charles Dugas, LA DWF, pers. comm.), Bayou Teche (Martha Griffis, USGS, pers. comm.), Boeuf (Louisiana Department of Wildlife and Fisheries, Inland Fish Division 2013), Caddo Lake, Lower Sabine, Toledo Bend Reservoir, Vermilion (Louisiana State University Herbarium 2010), Cross Bayou, Lower Red, Saline Bayou (Anonymous 2009), East Central Louisiana Coastal (Lund University 2010), Eastern Louisiana Coastal, Lower Red-Lake Iatt, Mermentau (Center for Invasive Species and Ecosystem Health 2015), Loggy Bayou (Rucker 2008), Lower Calcasieu, Upper Calcasieu (Charlie Dugas, LA DWF, pers. comm.), and Lower Pearl (Howard Rogillio, LA DFW, pers. comm.) drainages
  • Mississippi - Lower Leaf (Madsen et al. 2006), Lower Mississippi-Natchez (Mississippi Museum of Natural Science 2016), Middle Pearl-Strong (Madsen 2010), Pascagoula (Fuller et al. 2010), and Upper Leaf (Wunderlin and Hansen 2007) drainages
  • North Carolina - Black (Wayne Batten, NC State Univ., pers. comm.), Lower Cape Fear, New River, Northeast Cape Fear (University of Florida Herbarium 2016), and White Oak River (Kay Stratford, NC State Univ.,  pers. comm.) drainages
  • Puerto Rico - Cibuco-Guajataca (Felix Grana, PR DNER, pers. comm.), Culebrinas-Guanajibo, and Eastern Puerto Rico (Caudales et al. 2000) drainages
  • South Carolina - Broad-St. Helena (University of South Carolina 2016), Lower Savannah (SC DNR 2007), and Salkehatchie (Johnson 1995) drainages
  • Texas - Buffalo-San Jacinto (University of Florida Herbarium 2016), Caddo Lake (Johnson 2008), East Fork San Jacinto, Lower Brazos, Lower Sabine (Rhandy Helton, TX PWD, pers. comm.), Elm Fork Trinity, Lake O'the Pines, Lampasas, Lower Trinity-Kickapoo, Navidad, Upper Angelina (Texas Invasive Plant and Pest Council 2015), Lake Fork (Heidgerd 2015), Lake O' the Pines, Lower Neches, Middle Sabine, West Fork San Jacinto (Smith 2009), Lower Angelina (Texas Parks and Wildlife Department 2009), Lower Brazos-Little Brazos (Texas A&M University Bioinformatics Working Group 2007), Lower Trinity (Brown et al. 2009), North Galveston Bay (M. Hatch, NM DGF, pers. comm.), Sabine Lake (Kirk Blood, TX PWD, pers. comm.), Spring, West Galveston Bay (Ronald Jones, USFWS, pers. comm.), Toledo Bend Reservoir (Bister and Brice 2008a, Bister and Brice 2008b), and Upper Neches (Knight 2008) drainages, and Austin, Dallas, and Wichita Counties (Howard Elder, TX PWD, pers. comm.)
  • Virgin Islands - Crequie Dam of St. Croix drainage (Center for Invasive Species and Ecosystem Health 2015)
  • Virginia - private pond in Strasburg of North Fork Shenandoah drainage (Curtis Hutto, VA DCR, pers. comm.)

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: 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)

Anonymous. 2009. Salvinia control effort on Saline Lake proves successful.

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Bister, T.J., and M.W. Brice. 2008b. Lake Pinkston 2007 Survey Report. Texas Parks and Wildlife Department, Austin, TX.

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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.

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Heidgerd, D. 2015. Pesky invasive plant turns up in another east Texas waterway. Fort Worth, TX. Created on 11/24/2015. Accessed on 11/24/2015.

Johnson, D. 1995. Giant salvinia found in South Carolina. Aquatics 17(4):22.

Johnson, N.O. 2008. State gets tough to protect Caddo, other waterways. The Longview News-Journal, Longview, TX. 2008 (April 9). (accessed on 14 April 2008).

Knight, S. 2008. Unwanted plant's impact swift. Tyler Morning Telegraph, TylerPapercom, Tyler, TX. 2008 (February 14).

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

Revision Date: 3/15/2016

Peer Review Date: 3/18/2016

Citation Information:
Thayer, D.D., I.A. Pfingsten, C.C. Jacono, M.M. Richerson, and V. Howard, 2018, Salvinia molesta Mitchell: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL,, Revision Date: 3/15/2016, Peer Review Date: 3/18/2016, Access Date: 3/23/2018

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Citation information: U.S. Geological Survey. [2018]. Nonindigenous Aquatic Species Database. Gainesville, Florida. Accessed [3/23/2018].

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