ferny and Red azolla

Azolla pinnata / Azolla filiculoides

A small free-floating plant (0.8-3 cm long) that is green, reddish-green or reddish-purple in colour plants have a main stem with several branches regularly arranged on either side and are usually somewhat triangular in shape. These branches readily fragment from the base, leading to the formation of new plants. Its roots have numerous fine side branches that give them a feathery appearance its tiny overlapping 'leaves' (1-2 mm long) are alternately arranged along the branches and borne in two regular rows.

Common names 
Also known as: Ferny Azolla,
Flowering time 
Does not Flower
Native to Africa, the Indian sub-continent, eastern and south-eastern Asia and Australia. Native to large parts of northern, eastern and southern Australia (i.e. Queensland, New South Wales, Victoria, south-eastern South Australia and the northern parts o
Council declaration 
SIL – Special Investigation List
Known distribution 

Possibly naturalised beyond its native range in the coastal districts of south-western Western Australia.


A native plant that generally grows in freshwater swamps, wetlands, drainage channels, lakes, ponds and slow-moving waterways. However, it can sometimes be considered a weed when large populations take over dams, ponds and suburban waterways.


A small free-floating fern (0.8-3 cm long and 1-1.5 cm wide) that is often roughly triangular in shape. It is usually found covering the surface of still or slowly moving waterbodies.

Impact and control methods 

The presence of Azolla in a waterway is generally beneficial. However, in circumstances where waterways are extremely rich in nutrients, prolificgrowth may be a problem. It also is possible that thick, complete coverings of Azolla can cause de-oxygenation of the water.

Stem and leaves 

Plants have a straight main stem with several branches regularly arranged on either side (i.e. they are pinnately branched). These side branches zig-zag horizontally and are usually covered by the overlapping leaves. They are progressively longer towards the base, and the lower branches eventually produce side branches themselves. The stems are brittle and break easily, and the branches also fragment as the main stem decomposes, both of which lead to the formation of new plants. Roots are produced along the stems and these roots have numerous fine side branches (i.e. lateral rootlets), giving them a feathery appearance in the water. The tiny 'leaves' (i.e. fronds) are alternately arranged along the branches and are borne overlapping each other in two regular rows. These 'leaves' (1-2 mm long) actually consist of two rounded lobes (i.e. they are bi-lobed). The upper lobe is green, brownish-green, reddish-green, red or reddish-purple in colour, and the lower lobe is almost see-through (i.e. translucent). The upper surface of these 'leaves' is usually covered in minute hairs that give them a velvety appearance. These hairs make the 'leaves' totally water-repellant, and if plants are submerged they quickly refloat themselves with the right side up.

Flowers and fruits 

Tiny, round, spore-containing structures (i.e. spherical sporocarps) are sometimes produced at the bases of the side branches. These sporocarps (1-1.5 mm across) are brown in colour and are usually partially obscured by the 'leaves'.

Reproduction and dispersal 

Plants reproduce rapidly by fragmentation (i.e. by vegetative reproduction), as the basal branches separate from the main stem. They also produce spores at certain times of the year, particularly in late summer or as the margins of water bodies dry out.Plants and spores are spread by water, animals, vehicles, boats and other human activities.

Similar species 

Ferny azolla (Azolla pinnata) is very similar to red azolla (Azolla filiculoides), which is also present in south-eastern Queensland but less common. These two species can be separated by the following differences: ferny azolla (Azolla pinnata) plants have regularly branched stems and are usually somewhat triangular in shape. Their roots have numerous fine side branches (i.e. lateral rootlets) that give them a feathery appearance.red azolla (Azolla filiculoides) plants have irregularly branched stems and are usually irregular in shape. Their roots are simple and do not have any side branches (i.e. lateral rootlets). It is also relatively similar to some other floating aquatic plants, such as the duckweeds (Spirodela spp. and Lemna spp.) and young salvinia (Salvinia molesta) plants. However, the duckweeds (Spirodela spp. and Lemna spp.) are unbranched and always pale green in colour on top, while salvinia (Salvinia molesta) has numerous tiny eggbeater-shaped hairs on the upper surface of its 'leaves'.