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Symbiotic Nitrogen Fixing Bacteria -

The best known example of symbiotic nitrogen fixation is that of the Rhizobium group of bacteria which form nodules on the roots of leguminous plants.

Non leguminous trees and shrubs such as Alder, Ceanothus and Purshia have the nitrogen fixing actinomycete Frankia as the symbiont. Subtropical areas are widely colonized by Myrica and Casuarina.

These plants have similar symbionts. The water fern Azolla has Anabaena azollae as the symbiont. This organism fixes nitrogen within the leaf pores.

A considerable amount of nitrogen is fixed by non leguminous symbiotic systems which could be of great value in forests and specialized environments.