Salvinia minima
A floating fern invasive in the United States and South Africa.
Salvinia minima, also known as common salvinia or water spangles, is a floating aquatic fern that lives on the surface of calm waters. It originally comes from South America, Mesoamerica, and the West Indies, but was brought to the United States around the 1920s or 1930s. Internationally, it is considered an invasive species that can harm local ecosystems. It resembles giant salvinia (Salvinia molesta) but is a different species.
The fern’s leaves are small and oval, measuring between 0.4 and 2 centimeters long. Its rhizome floats near the water’s surface, with sets of three leaves branching off horizontally. Two of these leaves float on top, while the third is dissected and hangs underneath, acting like roots since the plant has no true roots. These hanging leaves are longer than the floating ones. The upper leaf surfaces are covered in fine white hairs that repel water; these hairs grow in groups of four and do not touch at the tips. Longer brown hairs are found on the leaf undersides. Leaves range from bright green to brown, often turning brown with age or in direct sunlight.
Salvinia minima goes through three growth stages. In the primary stage, a single bud or a few buds enter a new area, and the leaves lie flat on the water. In the secondary stage, as the ferns multiply, the leaves begin to curl upward. In the tertiary stage, the ferns become dense and form mats on the water’s surface, with leaves sometimes growing almost vertically due to crowding.
Reproduction happens asexually through fragmentation. Although the plant may produce sporocarps (spore sacs), it is believed to be sterile and can only reproduce by breaking apart. Any part of a rhizome that buds or breaks off can grow into a new plant. Because fragmentation can happen continuously, the fern often grows exponentially. Buds and rhizome fragments can also stay dormant during unfavorable conditions.
This fern typically grows on the surface of still or slow-moving freshwater, such as lakes, ponds, and canals. It can tolerate salinity levels of 4 to 7 parts per thousand (or a specific gravity of 1.003–1.005), so it also lives in brackish water like swamps, marshes, and wetlands. It can even be found in backyard ponds and private lakes, and it is sold in states where it is not banned as a noxious plant.
Quick Facts
- Genus
- Salvinia
- Species
- minima
Facts from the source article.
Lore & Background
Salvinia minima is a rootless fern with leaves growing in joined sets of three: two floating leaves and one dissected leaf that hangs underneath, acting as root-like structures. Fine white hairs on the leaf surface repel water and grow in groups of four without touching at the tips; longer brown hairs are present on the underside. Leaves range from bright green to brown, often browning with age and sunlight.
The species undergoes three growth stages: primary (leaves flat on water), secondary (leaves curl upward), and tertiary (dense mats with nearly vertical leaves). Reproduction occurs asexually through fragmentation, as the plant is thought to be sterile despite possible sporocarps. Any part of a rhizome that buds or breaks off can form a daughter plant, leading to exponential growth. Buds and fragments can remain dormant during unfavorable conditions.
Salvinia minima was first noted in the U.S. in the St. John's river in eastern Florida, likely transported by shipping boats in the late 1920s or early 1930s. It spread throughout Florida, then westward and northward, and is now present from Florida to New Mexico and in northern states including New York, Massachusetts, New Jersey, and Maryland, as well as Puerto Rico. It has also recently appeared in South Africa, spreading rapidly.
Reader's Guide
Salvinia minima is notable primarily as an invasive species that forms expansive mats on still or slow-moving freshwater, out-competing native plants such as duckweed. Its mats block sunlight, reduce dissolved oxygen, and can lead to fish kills, affecting waterfowl and commercial activities like crawfish and rice farming. Management efforts include mechanical removal, which is largely ineffective due to regrowth from fragments; chemical herbicides (fluridone, imazamox, penoxsulam) that can be effective but carry risks of harming non-target organisms and causing oxygen depletion; and biological control using the salvinia weevil Cyrtobagous salviniae, native to South America. A study by Louisiana State University in 2005–2006 compared the weevil to the salvinia stem-borer moth Samea multiplicalis, finding both feed on salvinia and control its spread. The species is listed as a noxious plant in Texas, where ownership and transport are prohibited. Its presence on the Global Invasive Species Database underscores its threat to biodiversity.
Did You Know?
- Salvinia minima is rootless; its dissected hanging leaves act as root-like structures.
- It reproduces only asexually through fragmentation, as it is thought to be sterile.
- The salvinia weevil Cyrtobagous salviniae, native to South America, is used for biological control.
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