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August 2023

General Informations

  • Algae are thallusic plants with chlorophyll, single or multicellular, and when multicellular, their bodies are not divided into parts such as root-stem and leaves.

  • Algae range in size from picoplankton, which are between 0.2 to 2 micrometers in diameter, to giant kelp, which can be 60 metres long.

  • Cells contain nuclei (nucleus) and chlorophyll. Reproduction occurs asexually (by spores) or sexually (by forming gametes); In primitive groups, reproductive cells (spores, gametes) are flagellated.

  • Asexual reproduction occurs directly by the division of cells into two. Sexual reproduction mostly occurs by isogamy (gametes that are the same in shape and size).

  • The increase in the density and prevalence of taste and odor producing Cyanobacteria (blue-green algae) in water resources is a growing global problem.

  • Climate change effects, such as temperature rise, and human activities, such as agricultural nutrient load, increase algal blooms.

  • The earthy-woody-musty tastes and odors most commonly reported in drinking water are known to originate from certain blue-green algae and actinomycetes and a few fungi.

  • Cyanobacteria are named in many ways, such as blue-green algae, blue-green, and cyanophyta.According to biologists, cyanobacteria are technically not algae, but are classified as photosynthetic bacteria.



  1. Chlorophyceae : Primarily freshwater

  2. Charophyceae : Charophytes are endemic to freshwater habitats, with some exceptions.

  3. Pleurastrophyceae : Freshwater and marine.

  4. Prasinophyceae (Micromonadophyceae) : Paraphyletic, primarily marine.

  5. Ulvophyceae : Primarily marine


  1. Bacillariophyceae (Diatoms) : Primarily in freshwater, marine, and soil environments.

  2. Bicosoecaceae : Freshwater and marine.

  3. Chrysophyceae (Golden Algae) : Freshwater and marine.

  4. Synurophyceae : Found mostly in freshwater

  5. Xanthophyceae (yellow-green algae) : Mostly in freshwater environments.

  6. Dictyochophyceae : Predominantly marine flagellates.

  7. Eustigmatophyceae : Mostly small, pale green, and spherical

  8. Phaeophyceae (brown algae or brown seaweeds) : Primarily in marine.

  9. Prymnesiophyceae (Haptophyceae) : Predominantly marine and planktonic.

  10. Raphidophyceae (Chloromonadophyceae) : Flagellates with mucocysts, occasionally found in freshwater or marine.


Cryptophyceae : They live in fresh and marine water, mainly in shaded environments where light levels are reduced relative to the surface.


Predominantly marine


Primarily in marine


Euglenophyceae : They are found in fresh water, especially when it is rich in organic matter.


Representative green algae

1. Halosphaera cf. minor; prasinophyte (photo by C. O'Kelly).

2. Two conjugating filaments of Spirogyra maxima; charophyte (photo by C. Drummond).

3. Klebsormidium flaccidum; charophyte (photos 3–9 by C. F. Delwiche).

4. Chlorokybus sp.; charophyte.

5. Marine macro-alga, Caulerpa; an ulvophyte.

6. Mesostigma; flagellate charophyte.

7. View of part of a Coleochaete orbicularis thallus, with eggs, charophyte.

8. Entransia fimbriata; charophyte.

9. Ulothrix sp.; ulvophyte.

10. Myrmecia sp.; trebouxiophyte (photo by V. Flechtner).

11. Colonial planktonic alga, Pediastrum duplex; chlorophyte.

12. Microthamnion sp.; trebouxiophyte. Figs.

13 and 14. Macroscopic and microscopic view of the water net, Hydrodictyon reticulatum from a pond in Connecticut; chlorophyte.

15. Nitella hyalina with orange sex organs; charophyte (photo by K. Karol).

16. Trentepohlia sp., with abundant orange secondary pigments forming a shaggy coat on rocks at Point Reyes, California; ulvophyte.

17. Chlorosarcinopsis sp.; chlorophyte (photo by V. Flechtner)

Microscopic view of green algae (Cladophora)

A.1. Chlorophyceae

A.2. Charophyceae

B.1. Bacillariophyceae (Diatoms)

Nearly all diatoms are microscopic - cells range in size from 2 µm to 500 µm, that is, half of a millimeter. The biggest diatoms are about the width of a human hair. Scientists use light microscopes (LM) or scanning electron microscopes (SEM) to view diatoms.

When diatoms are viewed with a light

microscope, the silica cell walls appear transparent (because we are seeing through glass). When diatoms are viewed with a scanning electron microscope, the cells appear opaque (because we are seeing the surface of the cell with electrons).

Images showing the diatoms

(a–f) Images of living cultures of

(a) C. Closterium (b) C. Meneghiniana (c) O. guenter-grassii

(d) P. borealis (e) S. Robusta (f) T. Weissflogii (Scale bar = 50 µm).

(g) Image of living cells of C. closterium (Scale bar = 10 µm).

(h–l) Images of oxidized culture material of

(h) C. Meneghiniana (i) P. borealis (j) S. Robusta

(k) O. guenter-grassii (l) T. weissflogii (Scale bar = 10 µm).

B.2. Bicosoecaceae

Bicosoecaeae cell scheme:

1) anterior flagellum,

2) phagosomes,

3) cytostome,

4) nucleus,

5) lorica,

6) posterior flagellum

B.3. Chrysophyceae (Golden Algae)

1) Chrysoreinhardia giraudii cells (bar 10 mm)

2) Chrysoreinhardia giraudii colony on Halopteris (bar 100 mm)

3) Unidentified Chrysophyceae (bar 10 mm)

B.4. Synurophyceae

B.5. Xanthophyceae (Yellow-green algae)

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Aug 03, 2023


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