Azolla - what is it?

Azolla  is an aquatic heterosporic fern, triangular or polygonal in shape. It floats on the water surface in ponds, ditches and paddy fields of tropical and warm temperate regions. Sometimes it gives the appearance of a green-reddish carpet, floating over the water. This genus is the only one of the Azollaceae family and has six to eight recognised species, belonging to two subgenera:

 

 

 

Azolla filiculoides
Azolla filiculoides




Azolla pinnata
Azolla pinnata

 

The plant has leaves with two lobes. In the dorsal lobe there is an ovoid cavity which contains a endosymbiotic community. This community is composed of two types of prokaryotic organisms: one species of nitrogen-fixing filamentous cyanobacteria - Anabaena azollae  Strasb and a variety of bacteria that some are identified as Arthrobacter  sp. and associated with other showing the presence of nitrogenase. As a consequence of this association, in some regions of the globe (Africa and Asia), Azolla  is used as a nitrogen biofertilizer, namely in rice fields.

Main characters of A. filiculoides  Lam. (subgenus Azolla ) and A. pinnata  var. africana  (subgenus Rhizosperma ).

 


Species
Vegetative characters Reprodutive characters
shape leaf
shape
leaf
margin
papillæ stomata nº of
floats
glochidia

A. filiculoides
polygonal obtuse 2-4
hyalin
layers


unicellular

2
gard.
cells


3
external,
fluked, aseptate
or rarely
septate near the
apex

A. pinnata
triangular acute 3-4
hyalin
layers
unicellular annular 9 internal
aseptate,
slightly curve.

 



In
TEIXEIRA, G., GOMES, E., DINIZ, M.A., JALÓ, C.T. & CARRAPIÇO, F., 1996 - “Azolla filiculoides Lam. e A. pinnata R. Br. subsp. africana (Desv.) R. M. K. Saunders & K. Fowler: Estudo biológico e químico”. Comunicações (IICT) - Série Ciências Agrárias, nº 14, IVªs. Jornadas de Engenharia dos PALOP’S (in press).

Other references

 


 

Last modified August 15, 2010
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