Nostoc filaments consist of uniformly-sized spherical or barrel-shaped cells, typically exhibiting a blue-green or olive green coloration. These filaments display various forms, including bent, kinked, or coiled structures, and are characterized by their extended, isopolar nature. These filaments are held together by a sturdy mucilage substance. Nostoc colonies vary widely, with some being microscopic and others macroscopic. They can possess smooth or warty textures and range from loose to dense in their arrangement. These colonies can appear spherical, flat, gelatinous, or form irregular mats. Spherical colonies are usually of marble-like size, though they can grow as large as 30-50 cm in diameter. The mucilaginous sheaths that envelop these colonies are robust and exhibit colors like yellow, brown, or black. They are most prominently visible in young colonies.