Salvinia rotundifolia, common salvinia, floating fern, Salvinia auriculata auct. non Aubl., Salvinia rotundifolia auct. non Willd.

Salvinia minima is believed to be a sterile species. It is not known to produce fertile spores and is postulated to be of hybrid origin (Schneller 1980). Regardless, sporocarps are common among the submersed leaves of large plants. Sporocarps are sac-shaped, and enclose smaller sacs (sporangia) that are formed to hold microscopic spores. Small (~1 mm wide) lemon-shaped sporocarps are attached in spirals along the main axis of the submersed filaments. For further details on identification, see Nauman 1993; Wunderlin 2000; Mickel and Beitel 1988; and Stoltze 1983.

The continuous branching and fragmentation of rhizomes turns out large volumes of vegetative daughter plants throughout the growing season. Copious hairy coverings minimize the desiccation of plants spotted on boats, trailers, alligators, turtles, and even dogs leaving the water. Lateral buds deeply embedded in the rhizome may lie dormant during periods of reduced moisture and cold temperature. Small rhizome fragments, commonly sheltered in associating vegetation, provide material for reintroduction on the return of favorable growing conditions.

This species prefers shallow backwaters of bayous, lakes and ponds, oxbows, ditches, slow-flowing streams, cypress swamps, and marshes (Lellinger 1985, Nauman 1993, Jacono et al. 2001). Like Salvinia molesta, S. minima is vulnerable to conditions of salinity. Biologists along the coast of southeastern Texas find Salvinia minima in their coastal study sites only during wintertime, when freshwater outflow is high and salinity measurements decline to 4 – 7 ppt. They regularly control Salvinia minima, and improve waterfowl habitat, by opening gates to allow saline water from the Gulf of Mexico into the bayous (Kirk Blood, Texas Parks and Wildlife Department, Port Arthur, Texas, pers. comm.). During August, on the Waterhole Branch of the Fish River, Alabama, Salvinia minima was registered as growing well with surface water salinity levels at 4 –5 ppt. (Scott Phipps, Weeks Bay National Estuarine Research Reserve, AL, pers. comm.).

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

Environmental	Socioeconomic

Potential pathway(s) of introduction: Stocking/planting/escape from recreational culture, escape from commercial culture, unauthorized intentional release, hitchhiking/fouling.

This species is commonly grown by aquarium and pond owners (Global Invasive Species Database, 2021), and is very commonly sold online through sites like eBay and Amazon. Synonym S. rotundifolia is cultured and sold in Ohio. Salvinia minima is still widely available in the water garden trade, either as a sale item or as a contaminant. Although it continues to infest new regions, it is not included on the Federal Noxious Weed List and is prohibited only in the states of Texas (Tex. Admin. Code §57.112 and §19.300) and Louisiana (La. Admin. Code tit. 76 § VII-1101) (USGS). It is commonly associated with commercially sold species, with one study showing it as a contaminant or hitchhiker up to 25% of the time in the sale of other species of retail aquatic plants (Maki and Galatowitsch 2004).

Status: Occasional populations rarely reported within the Great Lakes basin, but this species has not been reported to overwinter in the region.

Salvinia minima has a moderate probability of establishment if introduced to the Great Lakes (Confidence level: high).

While this species is highly adaptable to a variety of environmental variables and conditions, persistent low temperatures and ice cover in the region would provide significant barriers to establishment (Dickinson and Miller 1998; Flowgrow Aquatic Plant Database, 2021).

Great Lakes Impacts:

Salvinia minima has the potential for high environmental impact if introduced to the Great Lakes.
Mats of this plant can decrease oxygen concentration and block out sunlight, harming fish and other aquatic organisms in the area. Furthermore, die-offs of this species can reduce dissolved oxygen content in the surrounding area (Texas A&M AgriLife Extension, 2020). During earlier stages of colonization, Salvinia minima demonstrates exponential growth rates (Gaudet 1973). In Texas and Louisiana, S. minima typically occurs in dense, expansive populations and is known as a very troublesome weed that can completely blanket waterways (Jacono et al. 2001). Mats in Louisiana have been measured as thick as 20-25 cm (Montz 1989). An eight-year study at Jean Lafitte National Historic Park, Louisiana, found complete displacement of native Lemna species by Salvinia minima. (T. Doyle, LA, pers. comm.). An investigation of competition among Salvinia minima, Spirodela [Landoltia] punctata (G.F.W. Mey.) C.H. Thompson and Azolla caroliniana Willdenow in north Florida found Salvinia minima dominating the other species during the summer months (Dickinson and Miller 1998). Later in the season, S. minima was impacted by flooding and freezing and Spirodela punctata became the most abundant species (Dickinson and Miller 1998). In Texas, S. minima was observed shading out some submersed plant species (Jacono et al. 2001).

Salvinia minima has the potential for high socioeconomic impact if introduced to the Great Lakes.
Salvinia minima can clog water intakes for industry and power production if it forms dense surface mats (Jacono 2003). It can also negatively affect fisheries by changing macrophyte composition and reducing oxygen concentration (Texas A&M AgriLife Extension, 2020). Salvinia minima can restrict boating and impede waterway access due to excessive surface growth (Global Invasive Species Database, 2021).

Salvinia minima has the potential for moderate beneficial impact if introduced to the Great Lakes.
This species is sold as a common, inexpensive aquarium plant, and is often used in home aquariums in planted tanks due to its hardiness and ability to absorb excess nutrients (Global Invasive Species Database, 2021; Flowgrow Aquatic Plant Database, 2021).

Note: Check federal, state/provincial, and local regulations for the most up-to-date information.

Control
 

Biological
Biological control efforts for S. minima have focused on the salvinia weevil, Cyrtobagous salviniae, which is native to South America. It was introduced accidentally in Florida, a state in which water spangles are widespread but considered manageable. The manageable level of salvinia species, including both S. minima and Salvinia molesta (giant salvinia), is thought to be caused by the presence of these weevils, which live and feed on the salvinia leaves (Jacono et al. 2001).
The effects of these weevils on S. minima were compared to the effects of the salvinia stem-borer moth, Samea multiplicalis, which is a species native to the southern United States and is known to feed on other salvinia species in the same genus. Both the moth and the weevil feed on salvinia plants and control their spread (Tewari and Johnson, 2011). The lack of recorded detrimental environmental effects makes biological control methods the most promising in the long-term management of S. minima. Research continues to try to identify cold-tolerant populations that may be more suited to the region (Cozad et al 2019).

Physical
Mechanical methods include the physical removal of S. minima from areas where it is established, including raking the surface of the water or using large seine nets for removal. Mechanical methods have proven mostly ineffective because any fragments left behind will regrow, in addition to the difficulty of maneuvering equipment around small waterways (Texas A&M AgriLife Extension, 2020).

Chemical
Chemical herbicides that have been used with the best success on S. minima include the ingredients carfentrazone, copper complexes, diquat, fluridone, flumioxazin, glyphosate imazamox, and penoxsulam (Texas A&M AgriLife Extension, 2020). Some of these herbicides kill S. minima more successfully when a surfactant is added to make the chemicals stick to the surface of the leaves. However, if a large area of S. minima is sprayed with an herbicide all at once, the dead plant matter will sink and decompose, which can deplete oxygen in the water and result in fish kills and harm to other aquatic life. Smaller sections can be sprayed in sequence to reduce this side effect (Texas A&M AgriLife Extension, 2020).

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.