Azolla filiculoides

Water Fern

Family: Azollaceae

Azolla filiculoides, Water Fern, is a small, aquatic, free-floating fern, the individuals of which are about 2 cm across and fan-shaped.

It has a wide natural range across NSW, from the coast to the far western plains.

It is somewhat less common in other states, found in south-east and south-west Queensland, scattered sparsely in some parts of Victoria and the south-east and north-east of South Australia; and also recorded around Perth and further south in Western Australia. It may have a wider occurrence in these states with an under-representation of collections.

It has naturalised in some places and can act as a weed in many cases. It is known to be able to fix nitrogen rapidly, hence it can grow rapidly.

A. filiculoides is common in dams and other still bodies of water where it forms dense carpets.

The fronds range in colour from dark to light green to deep red in colour. They are only 2 mm long but clump together in alternate rows, in chain-like structures.

Being a fern, no flowers or fruits are produced. Rather, spores are produced. Species in this genus produce sporocarps of two sizes. One larger producing a megaspore and the other smaller producing microspores. However, they are rarely fertile in this regard and then to multiply by division.

In the garden

A. filiculoides has been used for mosquito control in rice fields. The dense mat makes it hard for mosquito larvae to breath.

This fern may be useful for gardeners who have dams or large water features to provide cover and habitat for frogs and fish or to control mosquitoes.

It propagates by spreading itself, so very easy to maintain. Likes to be in still water.

Beware that it can act as a weed in some instances and may need to be periodically controlled.


Propagation is by division but this happens without human intervention. Its biomass may double every 3-10 days. Excess plants may be removed with a net and used for compost.

Other information

The fern is not eaten by fish. A number of extinct species are known from the fossil record.

Azolla is a genus of about 6 species, existing over several continents in tropical and temperate areas. Australia has 2 species, occurring in all states. NSW currently has 2 species.

Azolla – Some meanings are reported online. One is Ancient Greek azo (ἄζω) can mean “to dry” and ollumi (ὄλλῡμῐ) means “to destroy” – alluding to the fact that this plant quickly dies if removed from water. It was found that Azote is an 18th-Century term for ‘nitrogen’ – coming from the Greek azotikos (άζωτικός) meaning “no-life” – as life cannot survive in this gas solely. The genus name may mean “nitrogen-associated” – referring to its abilitry to fix nitrogen. 

filiculoides – named for resembling the genus Filicula – which reportedly was a genus of ferns but is no longer.

This species is not considered to be at risk of extinction in the wild.

NSW Flora Online (PlantNET) – Azolla filiculoides profile page        https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Azolla~filiculoides

Wikipedia – Azolla filiculoides profile page https://en.wikipedia.org/wiki/Azolla_filiculoides

By Warren and Gloria Sheather. Editing and additional text by Dan Clarke