Common Name: Azolla

General Information

Azolla filiculoides is a small, evergreen, aquatic, floating fern, rarely larger than 25mm across. The plant spreads rapidly by budding, and is capable of quickly forming a dense mat of growth on the surface of the water. The foliage is bright green in shade, but develops attractive purplish-rose tints in full sun. All plants turn reddish-purple in the autumn as temperatures cool[, ].
The plant is an excellent source of nitrogen-rich organic matter, used for making compost, as a fertilizer etc, and is also used in water purification projects.
The plant has spread widely throughout the world by a variety of mechanisms, of which humans have become the most significant. It has been introduced into Europe, North and sub-Saharan Africa, China, Japan, New Zealand, Australia, the Caribbean and Hawaii. It grows rapidly in eutrophic water systems, easily outcompeting indigenous vegetation. The mat of growth on top of the water prevents light penetration; this, coupled with the decaying root and leaf matter below, creates an anaerobic environment which can reduce the quality of drinking water and make survival for other organisms in the water impossible[].

Known Hazards

None known

Botanical References

,

Range

Western N. America - British Colombia to California and Arizona; through Mexico and Central America to Colombia, Venezuela, Peru and southwards

Habitat

Stagnant and slow moving waters of ponds, lakes, marshes, swamps, and streams[].

Properties

Weed Potential	Yes
Medicinal Rating
Other Uses Rating
Habit	Perennial
Height	0.01 m
Growth Rate	Fast
Cultivation Status	Cultivated, Ornamental, Wild

Cultivation Details

Azolla filiculoides is is mainly found in frost-free climates in the wild and is not frost tolerant. In areas where it does experience frosts, it survives the colder weather by way of overwintering bodies that sink to the bottom in the autumn and rise to the surface in spring only after temperatures have warmed up. This phenomenon does not occur in all areas, nor is it effective if the winters are very cold. In such circumstances it is recommended that some plants be lifted each year in the autumn before the first frosts and overwintered in a saucer of moist soil in a bright frost-free area or in an aquarium - re-introducing them to the pond in the spring[, ]. Although of tropical origin, the plant is thought to have evolved a cold-tolerant strain since its introduction into Britain and South Africa, Some forms of the plant may be able to survive temperatures as low as -10°c before death occurs[].
Requires a sunny or lightly shaded position in still or slowly flowing water.
The plant is able to undergo rapid vegetative reproduction throughout the year by the elongation and fragmentation of the small fronds, and under ideal conditions, the daily rate of increase can exceed 15% with the doubling time being every 4 - 5 days[].
If growing this plant, it is very important to ensure that you do not spread it from your pond into the surrounding environment. The most simple way of ensuring this, when removing excess growth from the pond, is to put it into a black plastic bag, seal it and leave it for some weeks to make sure it is completely dead. The resulting material is then an excellent addition to the compost heap[].
Plants seldom reproduce by spores[].
The genus Azolla is unique in that it has a symbiotic relationship with a blue-green alga, (Anabaena azollae Strasburger), which is located in cavities in the dorsal leaf-lobes. This symbiotic association, which enables the plant to fix atmospheric nitrogen, is the only one known between a fern and a cyanobacterium[, ].

Edible Uses

None known

Medicinal

The plant has been used a cure for sore throats[].

Agroforestry Uses:

The plant is an exceedingly good source of nitrogen-rich biomass that can be used as a fertilizer or can be added to the compost heap[, ]. It has been studied for use in rice paddies where it acts as a fertilizer after it decomposes[].
The plant has acquired a common name of Mosquito Fern because its ability to completely carpet the surface of a pond is popularly believed to prevent mosquito larvae from developing and hatching[].
The plant is used for the purification of water, removal of heavy metals, and removal of nitrogen and phoshorous from wastewater. The fast-growing plant takes up these elements as it grows and the constant removal of excess growth takes these elements with it - for potential recovery and reuse[]

Other Uses

The plant has been used as an ingredient in soap production[].

Propagation

Spores -
Division - this is carried out quite naturally and very freely by the plant