permaculture

[Lawrence London <lfljvenaura@gmail.com>]

The Azolla Page
http://azolla.fc.ul.pt/index_ing.html
*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*, includes *A. filiculoides* Lam., A. *Rubra*  R.Br.
   (considered by some authors as a A. *filiculoides*  variety) , *A.
   caroliniana* Willd., *A. microphylla*  Kaulf. and *A. mexicana *Presl.;





*Azolla filiculoides
*[image: Azolla filiculoides]




 *Azolla pinnata
*[image: Azolla pinnata]



   - *Rhizosperma*  comprises *A. nilotica* Decne, *A. pinnata *R.Br. and *A.
   imbricata* (Roxb. ex Griff) Nak. (considered by some authors as a *A.
   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 ).*