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Weed Alert!

Salvinia molesta
(Giant Salvinia, Kariba weed, Aquarium watermoss)

Summary: known invader sighted in new areas
This plant has been detected in several bodies of water near the Texas/Louisiana border, and along the Colorado River. It is extremely invasive--any new infestations must be reported and eradicated immediately. A Task Force has been created to deal with the lower Colorado River infestation.

(Click on thumbnail images for a closer view)

Leaf hairs


Salvinia molesta is a water fern with a very high rate of reproduction. A complete description, including photographs of its unique leaf surfaces, spore-bearing structures, roots, etc., can be found at the Nonindigenous Aquatic Fern Resources Page.

Scientific and Common Names:
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!

Impacts and Considerations:
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!

Native Range:
Salvinia molesta is native to southeastern Brazil.

Range As An Invader:
Salvinia molesta 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.

1)Nonindigenous Aquatic Species (NAS) information resource for the United States Geological Survey Web Page, especially the page on ferns.
2)Cronk, Q.C.B, and Fuller, J.L., 1995, Plant Invaders, Kew, Great Britain. 3)Jacono, Collete, 1998, private communication.

--Barry Rice/Wildland Invasive Species Team; November 1998

Updated January 2005
©The Nature Conservancy, 1998