Common Australian Garden Weeds

Salvinia molesta

Scientific name: Salvinia molesta D.S. Mitchell


Habit of salvinia (Salvinia molesta) floating on water.


Close-up of the 'leaves' (fronds) of Salvinia.


Photo showing the feathery roots and spore sacs of Salvinia.


Close-up of Salvinia 'leaves' showing the water-repellent hairs on the upper surface.


Close-up of water repellent hairs.

Synonym: Salvinia auriculata Aubl. (misapplied)

Common name: Salvinia

Family: Salviniaceae

Origin

 

Native of south eastern Brazil.

Habit

 

A free-floating freshwater fern with branching horizontal stems and short feathery ‘roots’ (actually modified leaves), forming mats of foliage on the surface.

Habitat

 

This plant was introduced for the aquarium industry. Since becoming naturalised it has become a serious problem in rivers, streams lakes and dams. It is a problematic pest of rice fields around the world.

General description:

Stems and leaves: Individual plants can consist of as little as two hairy leaves (fronds) which float on the surface and a third leaf which is modified into feathery roots and remains submerged on a piece of stem (this 'plant' is called a ramet). Plants produce slender, branching runners, forming mats of vegetation very quickly. The emergent 'leaves' are oval or two-lobed with water-repellent waxy egg-beater shaped hairs in rows (leaf size varies from 1-1.5 x 2-5 cm). The submerged frond is brown and deeply divided.

Flowers and fruit Sterile spore sacs form along the filaments of the submerged root-like fronds. The plant reproduces by fragmentation (ie. vegetatively).

Distinguishing characteristics and similar species

 

A free-floating freshwater plant with two folded, hairy ‘leaves’ emerging from the water and a feathery root like structure hanging downwards. Plants form dense mats of vegetation on the water surface. Salvinia is quite distinctive and is rarely confused with other floating weeds such as water lettuce (Pistia stratoites) and water hyacinth (Eichhornia crassipes).

Noxious status

 

Declared noxious in all Australian states and territories.

Sources

 

Anonymous. (2000). NSW Agriculture. https://www.agric.nsw.gov.au. NSW Agriculture, Orange.

Anonymous. (2001). Weeds Australia. https://www.weeds.org.au. National Weeds Strategy Executive Committee, Launceston.

Jones, D.L. and Clemesha, S.C. (1989). Australian Ferns and Fern Allies. 3rd Edition. Reed Books, Sydney.

Kleinschmidt, H.E., Holland, A. and Simpson, P. (1996). Suburban Weeds. 3rd Edition. Department of Primary Industries, Brisbane.

Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious Weeds of Australia. Inkata Press, Melbourne.