Family: Salviniaceae (Water Fern Family)
Duration and Habit: Annual, Perennial Fern
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Salvinia is a rootless, floating aquatic fern. Emergent groups of leaves (fronds), oblong and flat (smaller growth forms) or semi-cupped/folded (larger growth forms), grow in chains and float on the water surface forming dense mats. Leaves grow in pairs and grow to approximately 1/2 inches wide and 1 inch long. Brown, thread-like leaves hang underwater, joining at a node along a horizontal, underwater stem and are similar in appearance to a root system. The upper surface of the green leaves is covered with rows of white, coarse hairs, acting as a water repellent. The hairs of giant salvinia are joined at the tips in an egg beater shape.
If you believe you have found giant salvinia in Texas, please report it here.
Native Lookalikes: Giant salvinia most closely resembles common salvinia (S. minima), also an invasive, which can be distinguished by inspection of the leaf hairs, which do not join at the tip. Another floating fern, azolla (Azolla caroliniana) (also called mosquito fern), could be mistaken for very small salvinia leaf forms. However, it has branching chains of leaves. Giant duckweed (Spirodela polyrrhiza) is sometimes mistaken for salvinia, but it is noticeably smaller and has flat leaves with no hairs and with purple undersides.
Common salvinia (S. minima)
Common salvinia's leaves (fronds) are not connected at the tip. (The insect is a salvinia weevil (Cyrtobagous salviniae), which is a biocontrol agent.)
Azolla (Azolla caroliniana)
Very different shape than giant salvinia, and note that it branches.
Giant duckweed (Spirodela polyrhiza)
Much smaller than giant salvinia. Note the leaves are flat and, relative to giant salvinia, smoother, and that they lack hairs.
Ecological Threat: Dense mats of salvinia shade out native aquatic species and decaying leaves can reduce dissolved oxygen levels in the water. Agricultural water use is impacted as salvinia obstructs intake pipes for irrigation. Recreational fishing, boating, and duck hunting are often significantly hindered by dense mats.
Biology & Spread: While salvinia may reproduce via spores as other ferns do, U.S. populations more commonly reproduce via budding from both attached nodes or broken stems. As many as five lateral buds can be found at one node. Populations can double every 2 weeks in the wild, and small quarter-acre ponds have been completely covered with giant salvinia in as little as 6 weeks from the point of invasion. Salvinia is easily spread by hitchhiking on boats and locally by birds and aquatic mammals and can also spread within water bodies and basins by wind, currents, and flooding.
History: Giant salvinia is a popular aquarium and water garden plant. It was first detected outside of aquarium and landscape cultivation in South Carolina in 1995, was found in Texas in 1997, and rapidly spread within Texas as well as to other southern states over the following years.
U.S. Habitat: Salvinia thrives in slightly acidic, high nutrient, warm, slow-moving freshwater. Found in streams, lakes, ponds, ditches, and even rice fields. Resistant to periods of low temperature, dewatering, and elevated pH levels. This invasive plant has low tolerance to salinity and does not tolerate brackish waters.
U.S. Nativity: Introduced to U.S.
Native Origin: Brazil
U.S. Present: AL, AZ, AR, CA, DC, FL, GA, HI, LA, MS, MO, NC, PR, SC, TX, VI, VA.
Distribution: The majority of infestations currently exist in Texas and Louisiana. Within Texas, giant salvinia is found in numerous lakes across the eastern region of the state and is frequently introduced into new lakes—see the mapping links below for current distribution information, as well as the USGS Nonindigenous Aquatic Species database point map.
List All Observations of Salvinia molesta reported by Citizen Scientists
Native Texas alternatives include
The best control is to prevent further infestations. Physical removal of giant salvinia can be effective in small areas such as boat slips but treatments with herbicides are necessary to control extensive infestations. Because giant salvinia is prohibited in Texas, a permit may be required for physical removal. Biocontrol using Salvinia weevils (Cyrtobagous salviniae) may also be effective although these weevils are not currently available to the public because production is limited and permits cannot be issued for possession and transport of the giant salvinia containing the weevils. A nuisance aquatic vegetation treatment proposal is required for chemical, physical, or biological control of any aquatic plant species on a public water bodyUSE PESTICIDES WISELY: ALWAYS READ THE ENTIRE PESTICIDE LABEL CAREFULLY, FOLLOW ALL MIXING AND APPLICATION INSTRUCTIONS AND WEAR ALL RECOMMENDED PERSONAL PROTECTIVE GEAR AND CLOTHING. CONTACT YOUR STATE DEPARTMENT OF AGRICULTURE FOR ANY ADDITIONAL PESTICIDE USE REQUIREMENTS, RESTRICTIONS OR RECOMMENDATIONS. MENTION OF PESTICIDE PRODUCTS ON THIS WEB SITE DOES NOT CONSTITUTE ENDORSEMENT OF ANY MATERIAL.
The Quiet Invasion: A Guide to Invasive Plants of the Galveston Bay Area. Lisa Gonzalez and Jeff DallaRosa. Houston Advanced Research Center, 2006.
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USDA Plants: Salvinia molesta
Invasive Plant Atlas of the United States: Salvinia molesta
Bugwood Network Images: Salvinia molesta