1. Cyanobacteria are aerobic, photosynthetic, N2 fixing microorganisms.
2. They are aquatic or terrestrial.
3. They may be free-living or symbiotic.
4. They may be heterocystous or nonheterocystous. Heterocyst is the site of nitrogen fixation.
5. e.g. Free living cyanobacteria are Anabaena, Nostoc, Tolypothrix, Plectonema, Oscillatoria.
6. Anabaena and Nostoc have symbiotic relationship with lichens.
7. Anabaena is also symbiotically associated with Azolla and Cycas.
