Sub-division :- Algae

Class :- Myxophyceae

Order :- Nostocales

Family :- Nostocaceae

Genus :- Nostoc

Nostoc commonly occurs in abundance after the first few rains. It is terrestrial as well as aquatic. It is collected from water pools, paddy fields, waterlogged soil, moist rocks, stagnant water, etc. It is known to occur as epiphyte on aquatic weeds and endophytically inside Cycas coralloid roots, Azollaa fern, Blasia and Anthoceros bryophytes and form lichens in association with fungal members.


Nostoc. A vegetative filament.


  • Thallus is colonial. Young colonies are microscopic, spherical and solid. 
  • Mature colonies become irregular and hollow. 
  • Colonial envelope encloses many filaments. These are much twisted, curved and entangled with each other. 
  • A filament has diffluent gelatinous sheath.
  • The trichomes are unbranched. Each trichome is made of cells of uniform size and shape except those called heterocyst which occur throughout. 
  • Structure of a cell is typically cyanophycean. It has a centrally located centroplasm, nucleus being altogether absent. Peripheral cytoplasm shows diffused pigments. A few shining cyanophycean granules are also present in this region. 
  • Heterocysts are intercalary. These are double walled, pale yellow coloured with two shining polar granules, one each near the neighbouring cell on either side. Heterocysts are much of the same size of slightly bigger than the vegetative cells. 
Nostoc. Heterocyst with akinetes on both of its sides.



  • Akinetes are developed only in a mature colony. These occur in large number, in series between two heterocysts. Usually all vegetative cells between two successive heterocysts develop into akinetes.
  • Akinetes are thick walled, sometimes ornamented, rich in food reserves and cyanophycean granules. 
  • Akinetes are liberated due to decay of colonial sheath. These germinate to form a new thallus.
Nostoc. Heterocyst with akinetes in chains.


  • Sub-division Algae
    1. Thallus simple,
    2. Chlorophyll present.
    3. Cell walls of cellulose.  
  • Class Myxophyceae
    1. Chromatophore not organised, pigments diffused, blue-green.
    2. Photosynthetic reserve cyanophycean starch.
    3. True nucleus absent.
    4. Sexual reproduction absent.
  • Order Nostocales
    1.  Thallus with trichomes, unbranched, or with false branching.
    2. Hormogones, heterocysts, exospores and endospores generally present.  
  • Family Nostocaceae
    1. Trichomes simple, unbranched, uniseriate and approximately of the same diameter throughout.
    2. Heterocysts and akinetes present,
    3. Trichomes not differentiated.
  • GenusNostoc
    1. Trichomes much twisted into a mass of definite form with a firm colonial envelope,
    2. Heterocysts intercalary and single.

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