Weeds in Australia


Salvinia molesta


Salvinia (Salvinia molesta) is a free-floating aquatic fern that can grow rapidly to cover the entire water surface with a thick mat of vegetation. The fronds are arranged along the stems in threes. Two fronds are leaf-like, more or less round in shape, 7-40 mm long and 7-25 mm wide, pale green to greenish brown, frequently overlapping and folded along the midrib (McCarthy 1998). The upper surfaces of these fronds are covered with distinctive eggbeater-shaped hairs 2-4 mm long that diverge into four branches near the top and fuse together at the tips (DiTomaso & Healy 2003). The third frond is submerged in water, root-like and slender, up to 30 cm long and covered with fine brown hairs. Salvinia plants are usually sterile. If sporocarps (spore sacs) are formed they are 2-3 mm long and borne in clusters along the root-like leaves. Spores, when produced, are not viable (McCarthy 1998).

For further information and assistance with identification of Salvinia contact the herbarium in your state or territory.


Salvinia has been introduced to coastal Western Australia, northern Northern Territory, southern South Australia, eastern Queensland, the central coast of New South Wales (McCarthy 1998) and at one site in north-east Victoria. It is naturalised in most coastal streams from Cairns in northern Queensland to Moruya on the south coast of New South Wales. It potential distribution includes water bodies in every Australian state and territory (CRC 2003).

Key points:
  • Salvinia (Salvinia molesta) is an aquatic fern introduced to Australia for use in aquaria and ponds.

  • It spreads vegetatively by stem fragments.

  • It can rapidly form dense mats that completely cover still or slow-moving water bodies.

  • It has distinctive egg-beater like hairs on the leaves.

  • It is a declared noxious weed for the whole of Australia.

How it spreads:

Salvinia molesta is probably of hybrid origin and is usually sterile (McCarthy 1998). When spores are produced they are not viable. Stem fragments are spread by various means including water movement. The dumping of the unwanted contents of ponds and aquaria is a major reason for the spread of Salvinia (CRC 2003).

Where it grows:

Salvinia is usually found in still or slow-moving water bodies with high nutrient levels. It can survive being frozen and water temperatures up to 43° C and salinities up to one tenth of sea water (CRC 2003).

Flower colour:No flower
Distribution map: Weed Distribution Map

Salvinia is a Weed of National Significance. It is regarded as one of the worst weeds in Australia because of its invasiveness, potential for spread, and economic and environmental impacts.


Salvinia forms dense mats over the water surface, severely modifying aquatic habitat for fauna, including birds, fish and invertebrates. Light is excluded and oxygen levels are reduced leading to water stagnation and pollution. The dense mats impede water flow, restrict stock access and provide favourable conditions for the breeding of disease-carrying mosquitoes. They can be mistaken for solid ground by people and animals with reported instances of animals falling into the water body beneath. Commercial and recreational fishing suffers dramatically with Salvinia plants blocking nets and impeding the passage of boats (Agriculture & Resource Management Council of Australia & New Zealand et al. 2003; CRC 2003).


Salvinia is native to south-eastern Brazil (CRC 2003).


Salvinia was probably first introduced to Australia by the aquarium trade. It was first reported as a weed near Sydney in 1952 and from Queensland in 1953. It is known to have been planted as an ornamental near Perth between 1950 and 1954 and has subsequently been grown in garden ponds in many other places including Melbourne, Adelaide and Alice Springs (Parsons & Cuthbertson 1992).


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