Salvinia natans
An annual floating fern that can cover entire water bodies.
Salvinia natans—also called floating fern, floating watermoss, floating moss, or water butterfly wings in the trade—is an annual aquatic fern that floats on the surface and can look a bit like moss. It thrives in still freshwater with plenty of sun and humid air, and it turns up around the world, though it’s especially common in Africa, Asia, and central Europe. In New York State and Massachusetts, it’s considered an introduced species.
The plant has two leaves about the size of a nickel that lie flat on the water, plus a third submerged leaf that acts as a root. Tiny air pockets inside the leaves keep it afloat, and a coating of cuticular papillae on the leaf surfaces repels water and protects against decay. Spore cases form at the base for reproduction.
By blocking sunlight from reaching far below the surface, *S. natans* creates safe, shaded breeding spots for many freshwater fish. But that same shade can cut off photosynthesis for underwater plants. Without ecological competition, the fern can eventually blanket entire ponds or lakes, starving out other plant species.
*Salvinia natans* is native across several continents. In Africa, it’s native to Algeria, Egypt, Libya, Morocco, and Tunisia. In Asia, it occurs naturally in Afghanistan, Azerbaijan, China, Cyprus, India, Indonesia, Iran, Iraq, Israel, Jordan, Kazakhstan, Lebanon, northwest Pakistan, Russia, Japan, Korea, Saudi Arabia, Syria, Taiwan, Thailand, Turkey, and Uzbekistan. In Europe, its native range includes Belarus, Belgium, Bulgaria, Czech Republic, France, Germany, Hungary, Italy, Moldova, the Netherlands, Poland, Romania, southern Russia, Slovakia, Spain, Ukraine, and the states of the former Yugoslavia. Archaeological and pollen evidence shows it was common in the Rhine/Meuse delta in the Netherlands during the Middle Holocene.
Quick Facts
- Genus
- Salvinia
- Species
- natans
Facts from the source article.
Lore & Background
Salvinia natans is found throughout the world where there is plentiful standing fresh water, sunlight, and humid air, but is especially common in Africa, Asia and central Europe. In New York State and Massachusetts, it is an introduced species. The plant has two nickel-sized leaves lying flat against the water surface and a third submerged leaf that functions as a root. Flotation is made possible by pouches of air within the leaves. Cuticular papillae on the leaves' surface keep water from interfering with the leaves' functioning and protect them from decay. Spore cases form at the plant's base for reproduction.
The leaves of S. natans block sunlight from reaching very far underwater. This is helpful to many freshwater fish, providing safe hiding places to breed in, but can interrupt the photosynthesis of many underwater plants. S. natans can eventually cover entire ponds or lakes without ecological competition, starving other plant species. Data from archaeological sites and pollen cores has shown that the species commonly occurred in the Rhine/Meuse delta in the Netherlands during the Middle Holocene.
Reader's Guide
Salvinia natans is significant as a widespread aquatic fern that can dominate freshwater ecosystems. Its ability to block sunlight and cover entire ponds or lakes without ecological competition makes it a powerful competitor that can starve other plant species. This characteristic is both beneficial and problematic: it provides safe hiding places for many freshwater fish to breed, but it also interrupts photosynthesis of underwater plants. The plant's native distribution spans multiple continents, including Africa, Asia, and Europe, with specific countries listed in the source. In New York State and Massachusetts, it is an introduced species. The plant's structure—two floating leaves and a submerged root-like leaf—along with air pouches for flotation and cuticular papillae for water repellency and decay protection, allows it to thrive in standing fresh water with sunlight and humid air. Its annual life cycle and reproduction via spore cases at the base contribute to its spread. Archaeological and pollen core evidence indicates its historical presence in the Rhine/Meuse delta during the Middle Holocene.
Did You Know?
- Salvinia natans has two nickel-sized leaves lying flat on the water and a third submerged leaf that functions as a root.
- Cuticular papillae on the leaves keep water from interfering with leaf function and protect from decay.
- In New York State and Massachusetts, Salvinia natans is an introduced species.
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