COMMON NAME

Giant salvinia
Water fern
Salvinia
Kariba weed
Aquarium watermoss

FULL SCIENTIFIC NAME

Salvinia molesta Mitchell

FAMILY NAME COMMON

Water fern family

FAMILY SCIENTIFIC NAME

Salvinia molesta

IMAGES

Habit

Sporangia

Habit in Water

NOMENCLATURE/SYNONYMS

Synonyms: None

DESCRIPTION

Botanical Glossary

Salvinia molesta is a free-floating aquatic fern that lacks roots. This plant has two types of leaves, emergent and submerged. The emergent leaves are green and obovate in shape. They measure around 2.2 cm (1 in.) long and 1.3 cm (0.5 in.) wide at maturity. On the surface of the leaves are many hairs that split and then rejoin at the tips, forming a cage like structure (some sources say that they resemble egg beaters). These hairs are water repellent. The submersed leaves are brown and feather-like in appearance, and are often mistaken for roots. Salvinia molesta has three stages of growth. In the first stage of growth, the emergent leaves are very small and lay on the surface of the water. In the second stage, the leaves start to curl at the edges. Finally, when the plants become tightly packed, the leaves take a more vertical position and pack together in chains. Egg-shaped sporocarps that contain sporangia, which in turn contain the spores, are found withing the submersed leaves. However, this plant is thought to be sterile in the United States, so often there are no spores in the sporangia.

SIMILAR SPECIES

Salvinia biloba Raddi (Giant salvinia)
Salvinia herzogii de la Sota (Giant salvinia)
Salvinia auriculata Aubl. (Eared watermoss)
Salvinia minima Baker (Water fern) Salvinia molesta is part of a complex of extremely similar-looking species that include S. biloba, S. herzogii, and S. auriculata. All of these species are on the Federal Noxious Weed List. Salvinia molesta also appears similar to S. minima. The key feature that differentiates these two species is that S. minima lacks the "egg beater" shaped hairs of S. molesta. Instead, the hairs of S. minima branch into four at the tips, but do not reunite at the top.

REPRODUCTIVE/DISPERSAL MECHANISMS

Salvina molesta reproduces vegetatively by means of stem fragmentation. Since these plants are small, they can be easily be moved by means of boats or waterfowl from one water body to another.

DISTRIBUTION

Salvinia molesta is native to Brazil. It has become invasive in many other parts of the world, such as Australia, New Zealand and Africa. In the United States this plant has been collected from North Carolina south to Florida and west to Texas, Arizona, California and Hawaii.

HISTORY OF INTRODUCTION IN NEW ENGLAND

Salvinia molesta has not yet been reported in New England.

HABITATS IN NEW ENGLAND

In its current range in the United States, Salvinia molesta is most often found in the calm waters of lakes and ponds. It can also be found in roadside ditches, slow-moving rivers, streams and water gardens. It cannot tolerate brackish water.

THREATS

Salvinia molesta is on the Federal Noxious Weed List due to the economic and environmental threats it poses. This plant is a rampant grower and can double its population in a week to ten days. It forms impenetrable mats (up to 3 ft. thick) that block sunlight and reduce oxygen in the water. It makes fishing, boating, swimming and other recreational activities impossible. It has had major detrimental impacts elsewhere in the world, which makes preventing its further spread in the United States a priority.

MANAGEMENT LINKS

Texas Agricultural Extension Service - Aquaplant

The Nature Conservancy

DOCUMENTATION NEEDS

Documentation required: Photograph or specimen
Best time for documentation: Summer, early fall

ADDITIONAL INFORMATION

Integrated Taxonomic Information System
Taxonomic information

PLANTS Database
General information and map

USGS Nonindigenous Aquatic Plant Distribution Information
Comprehensive information

The Nature Conservancy
Weed alert for Salvinia molesta

Arizona Department of Recreation
Description and picture of this plant

Texas Agricultural Extension Service - Aquaplant
Photograph, drawing and general information

Exotic Aquatics on the Move
Background information

Pacific Island Ecosystems at Risk (PIER)
Information about the threat of this species

Western Aquatic Plant Management Society
Description and images

United States Army Corps of Engineers
Fact sheet

National Invasive Species Information Center
Additional links and references

Invasive.org
Images and links

Center for Aquatic and Invasive Plants, University of Florida
Images and a map

Cary, P.R. and P.G.J. Weerts.  1984.  Growth of Salvinia molesta as affected by water temperature and nutrition. III. Nitrogen-phosphorus interactions and effect of pH.  Aquatic Botany 19: 171-182.

Cronk, Q.C.B. and J.L. Fuller. 1995. Plant invaders. Chapman & Hall, London.

Everitt, J.H., C. Yang, R.J. Helton, L.H. Hartmann, M.R. Davis.  2002.  Remote sensing of giant salvinia in Texas waterways.  Journal of Aquatic Plant Management 40: 11-17.

Fairchild, J.F., A.L. Allert, J.S. Riddle, D.R. Gladwin.  2002.  Efficacy of glyphosate and five surfactants for controlling giant Salvinia.  Journal of Aquatic Plant Management 40: 53-58.

Forno, I.W. and K.L.S. Harley.  1979.  The occurrence of Salvinia molesta in Brazil.  Aquatic Botany 6: 185-187.

Forno, I.W.  1983.  Native distribution of the Salvinia auriculata complex and keys to species identification.  Aquatic Botany 17: 71-83. 

Julien, M.H. and A.S. Bourne.  1986.  Compensatory branching and changes in nitrogen content in the aquatic weed Salvinia molesta in response to disbudding.  Oecologia 70(2): 250-257.

Lemon, G.D. and U. Posluszny.  1997.  Shoot morphology and organogenesis of the aquatic floating fern Salvinia molesta D.S. Mitchell, examined with the aid of laser scanning confocal microscopy.  International Journal of Plant Sciences 158(6): 693-703.

Oliver, J.D.  1993.  A review of the biology of giant salvinia (Salvinia molesta Mitchell).  Journal Aquatic Plant Management 31: 227-231.

Room, P.M. 1983. "Falling apart" as a lifestyle: the rhizome architecture and population growth of Salvinia molesta. Journal of Ecology 71: 349-365.

Room, P.M.  1990. Ecology of a simple plant-herbivore system: biological control of Salvinia. Trends in Ecology and Evolution. 5: 74-79.

Room, P.M. and M.H. Julien.  1994.  Population biomass and the absence of the -3/2 self-thinning rule in the clonal weed Salvina molesta.  Australian Journal of Ecology 19(1): 26-34.

Sale, P.J.M., P.T. Orr, G.S. Shell and D.J.C. Erskine.  1985. Photosynthesis and growth rates in Salvinia molesta and Eichornia crassipes. Journal of Applied Ecology 22, 125-137.

Thomas, P.A. and P.M. Room.  1986.  Taxonomy and control of Salvinia molesta.  Nature 320: 581-584.

USDA, NRCS.  2001.  The PLANTS Database, Version 3.1. (http://plants.usda.gov).  National Plant Data Center, Baton Rouge, LA 70874-4490 USA.