Types of Algae

Reproduction, Classification, Examples and Microscopy

Algae are photosynthetic organisms belonging to the kingdom Protista. Alga is the singular of algae with a changing size from microscopic unicellular micro-algae (Chlorella and Diatoms) to large massive kelps that are usually a length extending in meters (200 feet) and then there's brown alga.

One of the giant complicated species are seaweeds found in a marine habitat. The freshwater and most intricate type belong to kingdom Charophyta, for example, Spirogyra and the Stoneworts.   

Algae have photosynthetic pigments that are more complex and varied as compared to plants. They are ecologically beneficial for producing oxygen, together with a major contributing role in producing food for most of the aquatic life forms. Economically, they are used as a crude oil source and also in a number of pharmaceutical industries contributing to the assistance of mankind.

Cells of these organisms are quite different from the cells of plants and animals. Their cells usually lack xylem, phloem, and stomata that are most importantly present in land plants. There are many structures lacking in algae that are present in land plants like phyllids (resembling leaves) of bryophytes, leaves, roots and other essential characteristics of vascular plants. 


Algae reproduce by both sexual and asexual ways involving various reproductive strategies.  

Asexual reproduction occurs through ordinary cell division or fragmentation, without the union of cells or without the combination of different genetic material in minor algae species. In the case of superior algae, reproduction occurs through spores. 

Sexual reproduction typically comprises of meiosis using genetic material from two different parent cells. Different environmental events influence and regulate sexual reproduction.

There are normally two phases in the cycle of sexual reproduction. The first stage has one set of chromosomes and is known as haploid. The second phase is diploid having two sets of chromosomes. 

Algae Identification

Collection Methods 

Micro and macro-algae are collected using a knife or by hand. To distinguish reproductive cells, often a pocket microscope is used. This is important for some genera.

For example phytoplankton is collected using a mesh net. Water samples are kept overnight to settle or concentrate the algae towards the bottom.

In some cases, samples are squeezed to get more biomass, like in the case of Sphagnum. Samples that are present in soil are difficult to collect, therefore the culturing before the microscopic examination is done to get sufficient biomass. 

Important notes: Some data should be recorded before the next step of identification:

  1.     Name of collector
  2.     Date of collection
  3.     Locality of algae
  4.     The texture of water from which algae is collected
  5.     Algae either free-floating or attached


Place a drop of water or specimen on a microscope slide containing algae, gently cover the slide with a coverslip and view under a  microscope. Be sure to use a specimen of very small quantity to avoid clumping.

Observe slide in the microscopic range of about 40X or 100X magnification.

The hanging drop method can also be used for microscopic examination, in which the sample is taken on a coverslip and paraffin wax or liquid paraffin is used to examine. 


Using a compound microscope  a higher power greater than 100X would be necessary to properly observe specifics. 

Drawings or photographs are essential for algae to be properly identified, for this a camera attachment can be used.

Scanning and transmission electron microscopes are rarely used for this purposes they are only used for a few very small algae. 

Classification of Algae

Looking at the levels of organization “Phylum” and “Division”, both illustrate the same platform. The phylum is a zoology term and division is a botany term. Classification of protists is highly debated and any standard to outline them is not established.

However, based on some taxonomic variations we can outline their types as:

1. Chlorophyta

These are green algae having mitochondria with flat cristae, flagella, chloroplast, and zoospores. There are 9,000 to 12,000 species included in this category. The color of these species vary from yellowish green to dark green.

The majority are living in fresh water attached to rocks and wood. But some terrestrial and marine species are also found.

Green algae are also used for studying plant evolution, for example, single-celled Chlamydomonas are used for the ancestral study of land plants. 

Typically, they are both motile and non-motile having a central vacuole and a two-layered cell wall made up of cellulose and pectin.  They store food in the form of starch. These algae are varying in size and shapes. They are found as single-celled (Chlamydomonas), colonial (Volvox), filamentous (Spirogyra) and tubular forms (Caulerpa).

Chlorophyll is further divided into different classes. They are as follows:

a.    Chlorophyceae

These are freshwater including Chlamydomonas, Chlorella, Dunaliella, Oedogonium, and Volvox.

b.    Charophyceae

These are microscopic including Stonewort - Genus Chara, filamentous Spirogyra, and Desmids.

c.    Pleurastrophyceae

These are freshwater and marine including marine flagellate Tetraselmis.

d.    Prasinophyceae (Micromonadophyceae)

These are marine including Micromonas (sometimes classified with Mamiellophyceae), Ostreococcus, and Pyramimonas.

e.    Ulvophyceae

These are most important marine type including Acetabularia, Caulerpa, Monostroma, and sea lettuce (Genus Ulva). 

2. Chromophyta

This species is known for having chlorophyllide c(carotenoids), mitochondria with tubular structure cristae, zoospores, and biflagellate cells.

Classes included in this category are as follows:

a.     Bacillariophyceae 

These are also called diatoms. Characteristic features include silica cell walls and are bilaterally symmetrical. 12,000 to 15,000 species are present in this category including Cyclotella, Thalassiosira, Navicula, Nitzschia. 

Example: Cyclotella

Under the microscope they appear like little drum-shaped cells that are seldom present in chains. The controller valve view is most frequently seen. Valves are typically rounded with a divergent or concentric undulation of the valve appearance. The vital area of the valve appear clearly distinguished from the borderline zone.

The dominant central area is either structureless and immaculate or punctuate and is surrounded by the marginal zone with radial alveoli. Internal of the valve border is creased or chambered. 

b.     Bicosoecaceae

These types have colorless flagellate cells having a vaselike  appearance under the microscope. Their cells are attached to lorica with the help pf flagellum as a stalk. Lorica attaches to algae, plants, animals and water surfaces. There are 50 species included in this category. For example Bicosoeca and Cafeteria.

Example: Cafeteria

This is a tiny organism that is consumed by protozoa and small invertebrates. Their name indicates their importance in the foodweb. 

c.     Chrysophyceae 

These are also called golden algae. They range from unicellular to colonial flagellates comprising coccoid, capsid, filamentous, amoeboid, plasmodial and parenchymatous types. They are primarily freshwater with 12,000 species. For example Chrysocapsa, Lagynion, Ochromonas, Chrysamoeba. 

Example: Chrysamoeba

Under the microscope they appear like cells that are amoeboid, solitary or occasionally forming loose collections, sometimes with a very short frontal flagellum and a second condensed flagellum evident only by electron microscopy.

Amoeboid cells readily transform to be Chromulina-like with a longer anterior flagellum; usually retracted or only insufficient residual in this stage; transitional stages are common. 

d.     Dictyochophyceae

These are usually marine with silicoflagellates having diatomite deposits. Almost 25 species are included in this category.

There are two orders of this class;

  • Pedinellales

This type includes 6 chloroplasts in the radical organization with flagella base attached to nucleus directly.  For example Actinomonas, Parapedinella, Apedinella, Actinomonas, and Pteridomonas. 

  • Order Dictyochales 

They are called silicoflagellate  having silicon in their skeleton with flagella directly attached to the cell nucleus. For example Pedinella, Pseudopedinella, andDictyocha.

e.     Eustigmatophyceae

They are small and pale green with 15 species included in the group. For example Nannochloropsis and Eustigmatos. 

Example: Nannochloropsis

This species is a marine water micro-algae. All of these species are insignificant, nonmotile spheres which do not direct any dissimilar morphological feature and cannot be made eminent through either light or electron microscopy

f.     Phaeophyceae

These are called brown seaweeds of varying size ranging from small microscopic to large 20-meter size. They comprise 1,500 species that are usually marine. For example Laminaria, Macrocystis, Nereocystis, Pelvetia, Sargassum, and Pelagophycus. 

Example: Macrocystis

Macrocystis is a monospecific kind of kelp (large brown algae). This genus encompasses the majority of all the Phaeophyceae or brown algae. Macrocystis has pneumatocysts at the base of its edges. Sporophytes are recurrent and the individual may live for up to three years.  

g.     Prymnesiophyceae

As seen under the microscope, they appear to have hair like appendages between two flagella. They are important to reduce global warming because most of the carbon consumption occurring in the ocean is due to their activity.

They are mostly marine having 300 species in their group. For example Emiliania, Prymnesium, Phaeocystis, and Chrysochromulina. 

Example: Prymnesium

Prymnesium is a genus of haptophytes, including the species of Prymnesium parvum. These are a unicellular motile alga. It is ellipsoidal in figure as one flagellum is straight and there are two lengthier ones which allow movement. 


h.     Raphidophyceae 

These are flagellates with mucilage producing bodies and are mostly found in marine and freshwater areas. They include 50 species. For example Gonyostomum, Chattonella, Psammamonas, Heterosigma, Vacuolaria, and Psammamonas.

Example: Gonyostomum

Gonyostomum is a class of freshwater algae in the genus Gonyostomum, with worldwide distribution. They cause algae blooms which can be a nuisance and are known to cause allergic reactions to people swimming in lakes. 

i.     Synurophyceae

These are silica-scaled ranging in size from unicellular to colonial flagellates and cells are enclosed in silica scales. There are 250 species encompassed in this class. For example Synura and Mallomonas.

Example: Synura

Under the microscope they appear like balloon or pear-shaped chrysophycean cells, each with two golden chloroplasts, present in roundish motile colonies. Every cell has two flagella prominent outwards from the colony, and a stem fixed inward near to the colony center. Each cell is bound by spirally organized, colourless scales.

j.     Xanthophyceae

They are freshwater species that are coccoid, filamentous and capsid shaped. They include 600 species. For example: Tribonema, Vaucheria, Botrydium and Bumilleriopsis. 

Example: Vaucheria

Vaucheria is a type of Xanthophyceae or yellow-green algae. It belongs to one of two genera of  Vaucheriaceae. This class has filaments forming mats in either terrestrial or freshwater environments. 

Its strands form coenocytes with a great dominant vacuole pushing against the adjacent cytoplasm. The vacuole spread along the whole filament excluding its growing tip.

The chloroplasts are positioned on the sideline of the cytoplasm with the nuclei aggregating toward the center near to the vacuole.  

3. Cryptophyta

This division has all unicellular flagellates. 200 species are included in this category. For example Plagioselmis, Falcomonas, Rhinomonas, Teleaulax, and Chilomonas.

Example: Plagioselmis

Under the microscope they appear comma-shaped and look red or similar colors. Some strains within the genus seem to have a groove, while others do not. Investigators have recommended that those without grooves should be placed into a new genus.

4. Rhodophyta

These are mostly photosynthetic and filamentous, some are parasitic as well. There are almost 6,000 species included in this category. For example Corallina, Gracilaria, Kappaphycus, Corallina, Chondrus, Gelidium, Bangia, Palmaria, Porphyra, Polysiphonia, and Rhodymenia.

Example: Corallina

This species are characterized by a thallus that is solid because of calcareous deposits limited in the interior of the cell walls. The colors of these algae are most naturally pink, or others are shades of red along with purple, yellow, blue, white or gray-green. Corallina algae play a significant role in the biology of coral reefs. 

5. Dinoflagellata

They are usually unicellular with both photosynthetic and heterotrophic types having 1,500 species. They are called Dinoflagellates because they have two dissimilar flagella and are also have the characteristic of both plants and animals. For example Alexandrium, Dinophysis, Gymnodinium, Peridinium, Polykrikos, Noctiluca, Ceratium, Gonyaulax.

Example: Alexandrium

Alexandrium is one from the genus of dinoflagellates that have some of the most detrimental dinoflagellates because it forms toxic destructive algal blooms (HAB). There are almost 30 species of Alexandrium that can form a monophyleticclade. 

6. Euglenophyta

They are usually unicellular, photosynthetic and some are heterotrophic. Their chlorophyll is stored outside chloroplasts. There are 1,000 species in this category. For example Eutreptiella, Phacus, Euglena,and Colacium. 

Example: Eutreptiella

Under the microscope they appear with two or four flagella, pellicular with wide-ranging stripes, chloroplasts blistering from two paramylon hubs. This species are often very common in early spring. 

Related: Pond Water under the Microscope 

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