Nostoc Colony (Simplified)

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Nostoc is a prokaryotic, unbranched, filamentous, colonial blue-green alga belonging to the class Cyanophyceae. It is commonly known as star jelly, witches' butter, or mars egg.

This alga is found in both aquatic and terrestrial habitats and exists in a haploid form. The colony of Nostoc is globular and jelly-like, ranging in size from that of a pea seed to a plum fruit. It is surrounded by an outer firm gelatinous layer called the pellicle, which encloses a gelatinous matrix. The center of the colony remains hollow.

Within the gelatinous matrix, numerous filaments are present, with each filament referred to as a trichome. These filaments are enclosed by a mucilage sheath and consist of oval cells. The trichome is composed of three types of cells:

  • Vegetative cells
  • Heterocysts
  • Akinetes

Each cell is bounded by an outer cell wall and an inner plasma membrane. The cell wall is primarily composed of hemicellulose and pectin, while the plasma membrane encloses the protoplasm.


The protoplasm within the cells contains pigmented chromoplasm on the outer side and colorless centroplasm on the inner side. The chromoplasm contains thylakoids, Cyanophycean starch, pigment granules, and various pigments, including B-Carotene, Myxoxanthin, Zeaxanthin, Oscillatoxanthin, Phycoerythrin-c, Phycocyanin-c, and Chlorophyll-a. The stored reserve food in Nostoc is Cyanophycean starch.

Reproduction in Nostoc occurs through various vegetative and asexual methods, including colony fragmentation, hormogones, akinetes, heterocysts, and endospores. However, there is no sexual reproduction or alternation of generations observed in this alga. 

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