Taxonomic name: Azolla pinnata R. Br.
Common names: ferny azolla (English), mosquito fern (English), water velvet (English)
Organism type: aquatic plant
Azolla pinnata can spread rapidly, and has the ability to survive on moist soil in and around rivers, ditches, and ponds. It forms dense surface mats, which degrade water quality by reducing oxygen levels, and can interfere with boating, fishing and recreational activities.
"Plants small, 1.5 - 2.5cm long, with a more or less straight main axis with pinnately arranged side branches, progressively longer towards the base, thus roughly triangular in shape, the basal branches themselves becoming pinnate and eventually fragmenting as the main axis decomposes to form new plants. Roots with fine lateral rootlets, having a feathery appearance in the water. Leaves minute, 1 -2mm long, overlapping in 2 ranks, upper lobe green, brown green or reddish, lower lobe translucent brown; minute, short, plae, +/- cylindrical unicellular hairs often present on the upper lobes. When fertile, round sporocarps 1 - 1.5mm wide can be seen on the under side at the bases of the side branches. The leaves often have a maroon-red tinge and the water can appear to be covered by red velvet from the distance. The upper surface of the leaves are totally water-repellant, and if completely submerged the plants quickly refloat with the right side up."
lakes, ruderal/disturbed, water courses, wetlands
It has the ability to survive on moist soil in and around rivers, ditches, and ponds which may allow the plant to survive low water levels and periods of drought. (NC Aquatic Fact Sheet)
Azolla pinnata can spread very quickly forming dense vegetative masses on areas of still water. This in turn limits light available to other aquatic plants and oxygen used by other aquatic life. It forms dense mats that choke out other species. A. pinnata is on the US noxious weed list. In New Zealand has replaced a native floating fern, Azolla rubra, over most of northern New Zealand. Azolla lives in symbiosis with blue-green algae (cyanobacteria), taking advantage of their ability to fix nitrogen. It is sometimes introduced and used by farmers as a natural fertilizer for this reason.
Azolla is useful as a "soybean plant in rice field", because it can assimilate atmospheric nitrogen gas owing to the nitrogen fixation by cyanobacteria (blue green alga) living in the cavities located at the lower side of upper (dorsal) lobes of leaf. (Duke)
Native range: Africa and Madagascar, India, Southeast Asia, China and Japan, Malaya and the Philippines, the New Guinea mainland and Australia.
Known introduced range: Papua New Guinea, Australia, China, Japan, New Zealand, Vietnam, US.
Introduction pathways to new locations
Agriculture: Azolla lives in symbiosis with blue-green algae (cyanobacteria), taking advantage of their ability to fix nitrogen. It is sometimes introduced and used by farmers as a natural fertilizer for this reason. (PIER, 2003)
Transportation of domesticated animals: Possible introduced to New Guinea with cattle.
Azolla species can often grow on nitrogen poor water due to nitrogen fixing ability. However will grow very rapidly in high nitrogen habitats.
Generally it multiplies vegetatively, and by spores. In the right conditions A. pinnata can double its biomass in 5 to 10 days in the field. (Duke)
Compiled by: IUCN/SSC Invasive Species Specialist Group (ISSG)
Last Modified: Wednesday, 26 May 2010