Salvinia molesta D. Mitch.

Synonyms - Salvinia auriculata Aublet. S. molesta was previously included in S. auriculata. S. molesta is a discrete species to which all Australian material belongs.

Family: - Azollaceae.


Salvinia commemorates Prof. Salvini (1633-1729) of the University of Florence who assisted the botanist Pier Antonio Micheli (1679-1737).

Molesta is from the Latin molestus meaning annoying referring to the plants weedy nature.

Other names:

African Payal (India)

Kariba Weed (South Africa)

Karibaweed (USA).


Salvinia is a perennial, free-floating aquatic fern forming vast carpets with opposite, notched, flat or cupped leaves and fine, feathery 'roots'. Individual plants 50-300 mm long.




Floating leaves are produced in pairs at each node of a horizontal rhizome. Below each pair of floating leaves, attached by a short stalk is a single submerged leaf that is made up of a cluster of brown, feathery root-like segments. The floating leaves in the primary invading form and in plants growing in conditions of high nutrient status and low light are flat, heart-shaped and less than 15 mm across. Crowded plants form a dense mat, the internodes are short and the floating leaves are up to 30 mm in length, and broader than long with a deeply notched tip. In this form the leaves are often folded from the mid-rib.

Petiole - Short.

Blade - 3 forms;

Emergent leaves of primary invading form; green, well spaced, flat, egg shaped, deeply notched at the base and shallowly notched at the tip, 10-20 mm long by 8-15 mm wide, network veins close together. Pale elongated, 1mm long, waxy hairs with 4 branches that are joined at the tips to form a cage like structure that traps air on the upper surface and makes it non-wettable. Dense brown, matted hairs on the lower wettable surface.

Emergent leaves of secondary form; green, crowded together, folded or boat shaped, egg shaped to almost circular, notched at the base and rounded to shallowly notched at the tip. 25-60 mm long by 20-50 mm wide, network veins close together. Hairs similar to above. Entire lower leaf surface emersed in water.

Emergent leaves of tertiary form; green, crowded together and overlapping, tightly folded along the midrib and wavy, egg shaped to almost circular, deeply notched at the base and tip. 25-60 mm long by 20-60 mm wide(when flattened), network veins close together. Hairs similar to above. Midrib emersed in water and underside kept moist by capillary action because the leaves are closely pressed together.

Submerged leaves, on a short hairy stalk, brown, deeply divided in to hairy root like segments, 20-250 mm long.


Short rhizomes.


Sterile spores sacs are produced in small grape like bunches or racemes on the submerged root like leaf in dense infestations of the tertiary form.


Sterile aborted spores.


No true roots.

Slender, horizontal much branching rhizome just below the water surface and a modified leaf which looks like a many fine, unbranched, feathery vertical roots to 250 mm long.

Key Characters:

Free floating aquatic plant, 'roots' hanging freely in the water.

Floating leaves over 10 mm wide and covered with long hairs.


Life cycle:

Perennial. When the plant first invades a body of water it assumes what has been called the 'primary invading form' in which the leaves are small and the rhizomes are particularly fragile. After fragmentation each node is capable of developing into an independent plant. Leaves are produced in pairs at each node of the horizontal rhizome. As the infestation becomes denser the leaves become larger and leaf shape changes.


Optimum pH is 6-7.5.

Optimum temperature is 20-300C. Growth is retarded above 350C and below 100C.

Dry weight may double every 2.2 days under ideal conditions.

Primary form may have 700-1000 plants per m2 and a dry weight of 1.8-2.5 t/ha. Secondary form may have 900-1300 plants per m2 and a dry weight of 7-34 t/ha. Tertiary form may have 60-350 plants per m2 and a dry weight of 34-36 t/ha.


Sterile pentaploid hybrid, that reproduces vegetatively.

Flowering times:


Vegetative Propagules:

Buds at the stem nodes. Rhizome fragments.



Population Dynamics and Dispersal:

Salvinia is sexually sterile and all spread is vegetative by stem fragments breaking off and moving with the water flow. Much of the spread within Australia has been traced to plants discarded from aquaria or ornamental ponds.

Birds don't appear to move it, but animals may move it short distances after drinking.

Boats and machinery may move it from on water body to another.

The plant has three forms, the first occurs in low density infestations and is called the primary invading form has long and brittle stem internodes and small, flat leaves. The second form is at moderate densities where there is open water and has reduced internode length, larger leaves. The third form is mat forming and occurs a very high densities where there is no open water left and the rhizomes are very short, the leaves crowded and overlapping.

Origin and History:

Central and Southern America. South east Brazil.

Probably introduced as an aquarium plant in the late 1940's.

First recorded in NSW in 1952, QLD in 1953, WA in 1950-54, NT in 1976.



Naturalised in Malaya, Africa, Sri Lanka, India and New Zealand.


Found in a drain that flows into the Brunswick River near Australind Senior High School in 2001.


In still and slow flowing fresh or slightly brackish water or frequently flooded areas with a water temperature of 100C-350C.


Tropical. Sub Tropical. Warm Temperate.


Free floating aquatic plant.

Plant Associations:

Water Hyacinth, Potato vine, Hornwort, Persicaria spp.



Removes nutrients and heavy metals from water and has potential for water purification.

It has potential for bio-gas production generating 8.8 litres per kilogram fresh weight or more.

Suppresses other weeds and insects of rice.


Very serious weed of waterways, reservoirs, streams and rice fields.

Taints water, blocks and interferes with irrigation and hydro electric equipment.

Interferes with boat traffic and navigation, fishing and recreation.

Salvinia is capable of very rapid growth. (A creek near Rockhampton was completely covered over a distance of 12km in eighteen months).

Dense mats of the plant result in the water having a lowered oxygen concentration, a higher carbon dioxide concentration, lower pH and a high content of decaying plant material which adversely affect the flora and fauna and degrades the water for domestic or stock use.

Competes with rice and may lead to the abandonment of the fields.


Not recorded as toxic.


Noxious weed of NSW, NT, QLD, SA, TAS, VIC and WA.

Secondary and prohibited weed of Tasmania.

Management and Control:

Mechanical removal is usually inefficient and expensive and often leads to a spread of the infestation.

Infusions of sea water into streams has provided control in WA.

Herbicides such as diquat, AF100(kerosene plus calcium dodecylbenzene sulphonate), diuron, hexazinone, chlorsulfuron and fluridone give good control of primary and secondary forms but reinfestation is often rapid due to the nutrients released by the dying weed.

A combination of control methods including herbicides is usually the most effective.

Biological control is the most effective for the tertiary form.


Eradication strategies:

Difficult but not impossible to eradicate. Use a combination of the control methods listed above. Most infestations in WA have been eradicated.

Herbicide resistance:

Biological Control:

Controlled by a by an introduced weevil (Cyrtobagous salviniae), a pyralid moth (Samea multiplicalis) and an acridid grass hopper (Paulinia acuminata).

Related plants:


Plants of similar appearance:

Azolla is similar but much smaller.


Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P14. Photo.

Hussey, B.M.J., Keighery, G.J., Cousens, R.D., Dodd, J. and Lloyd, S.G. (1997). Western Weeds. A guide to the weeds of Western Australia. (Plant Protection Society of Western Australia, Perth, Western Australia). P12. Photo.

Hyde-Wyatt, B.H. and Morris, D.I. (1980) The Noxious and Secondary Weeds of Tasmania. (Tasmanian Department of Agriculture, Hobart, Tasmania). P124-125. Diagrams.

Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).

Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #1084.1.

Marchant, N.G., Wheeler, J.R., Rye, B.L., Bennett, E.M., Lander, N.S. and Macfarlane, T.D. (1987). Flora of the Perth Region. (Western Australian Herbarium, Department of Agriculture, Western Australia). P55.

Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious weeds of Australia. (Inkata Press, Melbourne). P18-22. Photos.


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