Azolla
The Azollacea are a very small free floating aquatic fern. The Azollacea has 1 genus with 6 species and is wide spread through tropical and sub-tropical regions. The stem of this particular fern is short. The plant grows in a creeping like fashion.
figure 1.1 Azolla in water body.(USA: Texas: cultivated, 2004.Image at PlantSystematics.org)
Conservation code: not threatened native to Western Australia
Nill
The Azollacea are a very small free floating aquatic fern. The Azollacea has 1 genus with 6 species and is wide spread through tropical and sub-tropical regions. The stem of this particular fern is short. The plant grows in a creeping like fashion. The underside of the plant has small roots and sometimes having fine out growths. The leaves on the Azollacea family are generally small and overlap each other. The leaves are fleshy with the margins being transparent. The leaves consist of two lobes with the upper lobe usually being 1 to 2 mm in length. They are usually small but it can have a cone like structure jetting out. The leaves also lack veins the veins. In the central cavity of the plant contain cyanobacterium. With the lower lobe of the plant being submerged under water. The lower lobe of the Azollacea bear 2 to 4 megasporangia or microsporangia in axils. The megasporangia are a long round shape that have pitted marks across the surface. The microsporangia can range from 7 to 100 pods depending on the plant the plants microsporangia are stalked and round shaped and contain 4 to 10 microspores.
Figure 1.2 diagram of Azolla
Azolla
The Azolla fern is an aquatic fern that can completely cover a water source, the fronds on this particular plant are oval shaped or have a triangular outline. The Azolla fern has abundant leaves that reside in two rows. The upper lobe of the leaf is generally covered in a blue green algae know as Anabaena. The leaves are held above the water surface with the second row of leaves the lower lobe submerged in the water, the leaves are thin and bearing in axils 2 to 4 megasporocarps or microsporocarps. The megasporocarps are obloid in shape and have a pointed tip. The microsporocarps on the Azolla are egg shaped or can be spherical with each containing 32 - 64 microspores, both the megasporocarps and the microsporocarps are protected by a membrane like indusium. Azolla is one of five fern genera to exhibit a heterosporous life cycle(Metzgar, Schneider et al. 2007). This particular phenomenon is only observed in less than 1% of all ferns(Metzgar, Schneider et al. 2007).
The family for Azolla is Azollacea. This family consists of 1 genus and 7 species which are ,Azolla caroliniana, Azolla cristata Kaulf, Azolla filiculoides Lam, Azolla imbricata (Roxb. ex Griff.) Nakai, Azolla mexicana C. Presl, Azolla microphylla Kaulf, Azolla pinnata R. Br. .
Azolla have undergone an evolutionary reduction of the sporophytes to enable a greater buoyancy of the plant(Saunders and Fowler 1993). The smaller size of the mature plants also enable a quick colonization of a new body of water by vegetative reproduction(Saunders and Fowler 1993).
Azolla is found across the world from South-,Central-, and North America to Africa, India, Ceylon, Japan and Australia it was introduced to New Zealand.
The Azolla fern can survive on moist soils and in rivers and around the river bed, the Azolla fern also has the ability to survive in ditches, and ponds as well as areas that have low water levels during times of drought. the plant is mainly found in warm tropical areas.
Because of its agricultural importance Azolla lam is the most frequently studied genus of fern in the world(Metzgar, Schneider et al. 2007). Azolla has an obligated symbiotic association with the cyanbacterium anabaena Azolla strasbuger. This symbiotic process has been appreciated because of it ability fix nitrogen from the atmosphere which it is usually unable to obtain. The use of Azolla as green manure in agriculture such as rice fields(Metzgar, Schneider et al. 2007)
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