Salvinia molesta

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Authors: Barry Rice, Global Invasive Species Team, The Nature Conservancy


Kingdom: Plantae
Phylum: Pteridophyta
Class: Filicopsida
Order: Hydropteridales
Family: Salviniaceae
Genus: Salvinia
Species: S. molesta
Scientific Name
Salvinia molesta
D. S. Mitchell
Common Names

giant salvinia, kariba weed, salvinia, water fern, aquarium watermoss


Salvinia molesta is an aquatic fern that floats on the surface of the water. Submerged fronds are “stringy” and resemble roots.
Floating leaves are 0.5-1.5 in. (2.5-3.8 cm) long, oblong, and vary in color from green to gold to brown. The surfaces of the leaves have rows of arching hairs that look like little egg-beaters. When young, leaves are smaller and lie flat on the surface of the water.
This plant does not produce flowers.
S. molesta reproduce by spores and by budding of broken stems or attached nodes.
Ecological Threat
After maturing, S. molesta forms chains of leaves that run together to form thick mats on the surface of the water. These mats restrict oxygen and light availability causing death of the primary producers and disrupting the aquatic food chain. S. molesta is on the Federal Noxious Weed list and can invade most any type of aquatic system. The plant is native to South America and was first introduced into North America as an ornamental.


Salvinia molesta D.S. Mitch. is closely related to Salvinia auriculata Aubl. The common names "giant salvinia" and "aquarium Watermoss" refer to its size and use in freshwater aquaria. "Kariba weed" is a reference to its type collection location in Lake Kariba--ironically enough, in Rhodesia where it is an invading species!

Stewardship summary

Salvinia molesta is a water fern with a very high rate of reproduction.

1) This extremely rapidly reproducing plant can double its numbers in as little as 2-10 days, completely dominating waterways.

2) Extremely small fragments are effective, viable propagules.

3) Spore viability is unknown.

4) The plant is federally prohibited in the US, and is therefore illegal to sell or possess!

Natural history

Salvinia molesta is native to southeastern Brazil. It has been spread to many part of the world, perhaps initially by the aquarium and garden-pond trades. It is a serious weed in New Guinea, Australia, Mauritius, Africa, India, Sri Lanka, Ceylon, New Zealand, and elsewhere. In the US it has been observed in South Carolina (eradicated), Texas, and Lousiana. (In October 2000, it was discovered in a number of sites in southeastern North Carolina.) It represents a significant danger in any warm, slow-moving bodies of water. Any area which might support water hyacinth (Eichhornia crassipes) is probably at risk.


It is vital that infestations of all sizes are reported and completely eradicated. Authorities in Texas note that the Salvinia population at one infestation has exploded so rapidly, in just a month, that chemical control is their only viable alternative.

1) The most straightforward control is by preventing additional infestations. Salvinia reproduces so rapidly that infestations rapidly become impossible to eradicate using manual methods!

2) A biocontrol has been developed (Cyrtobagous salviniae) and may be effective in the near future. Until then chemical control may be the only viable option available.


Information sources


  • Anonymous 1998. Nonindigenous Aquatic Species (NAS) information resource for the United States Geological Survey Web Page, especially the page on ferns, accessed 1998.
  • Cronk, Q.C.B, and Fuller, J.L., 1995, Plant Invaders, Kew, Great Britain.
  • Jacono, Collete, 1998, private communication.

Source document

Weed Alert: Salvinia molesta; Barry Rice, 1998.

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