Frankia is a genus of filamentous, nitrogen-fixing bacterium and it forms a symbiotic relationship with many plants. It causes root hair deformation in a way that it enters the cortical cells and induces the nodule formations, which look like those induced by Rhizobium in legumes. It is associated symbiotically with the root nodules of several non-legume plants like Casuarina, Alnus, Rubus etc. It cannot fix nitrogen in free state.