These are the nitrogen fixer Cyanobacteria (Blue green algae) under order Nostocales. They have this ability due to a specialized cell, known as Heterocyst.
- Heterocyst identification key Features with respect to vegetative cells.
- Thick walled.
- Weak pigmentation.
- Present at both intercalary and terminal position.
- Intercalary Heterocyst have Polar granules at each pole while Terminal Heterocyst have polar granule at single pole.
- Neither divide nor Dedifferentiate.
- Fix nitrogen under Aerobic condition.