Algae Classification and Characteristics

In this algae classification and characteristics post we have briefly explained about general features, reproduction, classification, and economic importance.

Algae are simple plants that lack true roots, true stems and true leaves. Two-third of our earth’s surface is covered by oceans and seas. The photosynthetic plants called algae are present here. More than half of the total primary productivity of the world depends on this plant group. Further, other aquatic organisms also depend upon them for their existence.

Algae are autotrophs that can develop in a variety of environments. The majority of them are aquatic, marine (Gracilaria and Sargassum), and freshwater (Oedogonium and Ulothrix), and they can also be found in soil (Fritschiella, and Vaucheria).

Chlorella lives in Hydra and sponges as an endozoic organism, whereas Cladophora crispata grows on mollusk shells. Algae have evolved to flourish in a variety of severe environments. Dunaliella salina is a salt pan bacterium (Halophytic alga). Cryophytic algae are algae that develop in snow. Chlamydomonas nivalis is a red-colored fungus that grows in snow-covered slopes (Red snow). Epiphytic algae are algae that grow on the surface of aquatic plants.

General Features

The algae show a great diversity in size, shape and structure. A wide range of thallus organisation is found in algae. Unicellular motile (Chlamydomonas), unicellular non-motile (Chlorella), Colonial motile (Volvox), Colonial non motile (Hydrodictyon), siphonous (Vaucheria), unbranched filamentous (Spirogyra), branched filamentous (Cladophora), discoid (Coleochaete) heterotrichous (Fritschiella), Foliaceous (Ulva) to Giant Kelps (Laminaria and Macrocystis).

Algae are Eukaryotes except blue green algae. The plant body does not show differentiation into tissue systems. The cell wall of algae is made up of cellulose and hemicellulose. Siliceous walls are present in diatoms. In Chara the thallus is encrusted with calcium carbonate. Some algae possess algin, polysulphate esters of polysaccharides which are the sources for the alginate, agar agar and Carrageenan.

The cell has a membrane bound nucleus and cell organelles like chloroplast, mitochondria, endoplasmic reticulum, golgi bodies etc., Pyrenoids are present. They are proteinaceous bodies found in chromatophores and assist in the synthesis and storage of starch. The pigmentation, reserve food material and flagellation differ among the algal groups.


Algae reproduce by vegetative, asexual and sexual methods. Vegetative reproduction includes fission (In unicellular forms the cell divides mitotically to produce two daughter cells Example: Chlamydomonas); Fragmentation (fragments of parent thallus grow into new individual Example: Ulothrix) Budding (A lateral bud is formed in some members like Protosiphon and helps in reproduction) Bulbils, (a wedge shaped modified branch develop in Sphacelaria) Akinetes (Tick walled spores meant for perennation and germinates with the advent of favourable condition Example: Pithophora). Tubers (Structures found on the rhizoids and the lower nodes of Chara which store food materials).

Asexual reproduction takes place by the production of zoospores(Ulothrix, Oedogonium) aplanospore(thin walled non-motile spores Example: Vaucheria); Autospores (spores which look similar to parent cell Example: Chlorella); Hypnospore (thick walled aplanospore – Example: Chlamydomonas nivalis); Tetraspores (Diploid thallus of Polysiphonia produce haploid spores afer meiosis).

Algae Diagram with Labels

Features of Algae

Algae Diagram with Labels, Image Source:

Sexual reproduction in algae are of three type 1. Isogamy (Fusion of morphologically and Physiologically similar gametes Example: Ulothrix) 2. Anisogamy (Fusion of either morphologically or physiologically dissimilar gametes Example: Pandorina) 3. Oogamy (Fusion of both morphologically and physiologically dissimilar gametes. Example: Sargassum). Te life cycle shows distinct alternation of generation.

Algae Classification and Characteristics


F.E. Fritsch proposed a classification for algae based on pigmentation, types of flagella, reserve food materials, thallus structure and reproduction. He published his classification in the book “The structure and reproduction of the Algae”(1935). 


The members are commonly called ‘Green algae’. Most of the species are aquatic (Fresh water-Spirogyra, Marine -Ulva). A few are terrestrial (Trentipohlia). Variation among the shape of the chloroplast is found in members of algae. It is Cup shaped (Chlamydomonas), Discoid (Chara), Girdle shaped, (Ulothrix), reticulate (Oedogonium), spiral (Spirogyra), stellate (Zygnema), plate like (Mougeoutia).

Chlorophyll ‘a’ and Chlorophyll ‘b’ are the major photosynthetic pigments. Storage bodies called pyrenoids are present in the chloroplast and store starch. They also contain proteins. The cell wall is made up of inner layer of cellulose and outer layer of Pectin. Vegetative reproduction takes place by means of fragmentation and asexual reproduction is by the production of zoospores, aplanospores and akinetes.

Sexual reproduction is present and may be isogamous, anisogamous or Oogamous. Examples for this group of algae includes Chlorella, Chlamydomonas, Volvox, Spirogyra,Ulothrix, Chara and Ulva.


The members of this class are called ‘Brown algae’. Majority of the forms are found in marine habitats. Pleurocladia is a fresh water form. The thallus is filamentous (Ectocarpus) frond like (Dictyota)or may be giant kelps (Laminaria and Macrocystis). The thallus is differentiated into leaf like photosynthetic part called fronds, a stalk like structure called stipe and a holdfast which attach thallus to the substratum.

The Pigments include Chlorophyll a, c, carotenoids and Xanthophylls. A golden brown pigment called fucoxanthin is present and it gives shades of colour from olive green to brown to the algal members of this group. Mannitol and Laminarin are the reserve food materials. Motile reproductive structures are present. Two laterally inserted unequal flagella are present. Among these one is whiplash and another is tinsel.

Although sexual reproduction ranges from isogamy to Oogamy, Most of the forms show Oogamous type. Alternation of generation is presented (isomorphic, heteromorphic or diplontic). Examples for this group include Sargassum, Laminaria, Fucus and Dictyota.


Members of this group include ‘Red algae’ and are mostly marine. The thallus is multicellular, macroscopic and diverse in form. Porphyridium is the unicellular form. Filamentous (Goniotrichum) ribbon like (Porphyra) are also present. Corallina and Lithothamnion are heavily impregnated with lime and form coral reefs.

Apart from chlorophyll A, r-phycoerythrin and r-phycocyanin are the photosynthetic pigments. Asexual reproduction takes place by means of monospores, neutral spores and Tetraspores. he storage product is floridean starch. Sexual reproduction is Oogamous. Male sex organ is spermatangium which produces spermatium. Female sex organ is called carpogonium.

The spermatium is carried by the water currents and fuse with egg nucleus to form zygote. The zygote develops into carpospores. Meiosis occurs during carpospore formation. Alternation of generation is present. Examples for this group of algae include Ceramium, Polysiphonia, Gelidium, Cryptonemia and Gigartina

Economic Importance


It essential source of nutrition for many cultures across the world. Algae is a prominent element in a variety of local dishes in European countries such as Ireland, Scotland, France, Germany, Norway, and Sweden, as well as populations in North and South America and Asian countries such as China and Japan.

Algae are high in carbs, lipids, proteins, and vitamins A, B, C, and E, among other nutrients. It is not only a low-cost source of protein for many people throughout the world, but it also provides a variety of critical minerals like iron, potassium, magnesium, calcium, manganese, and zinc.


Algae, particularly seaweed, is fed to a wide range of farm animals. Rhodymenia palmate, sometimes known as “Sheep’s weed,” is a plant that is used to feed livestock such as cattle and poultry. It is utilized as feed in a number of countries, including Sweden, Denmark, and Norway in northern Europe, as well as Scotland, China, New Zealand, and North and South America.


Algae is used in the production process of the fish breeding and farming sector, often known as pisciculture. According to scientists, a range of fish species enjoy eating various types of algae, the most frequent of which being blue-green and green algae, as well as microalgae.


Large red and brown are the most prevalent kind of algae used in fertiliser production. These two forms of algae are particularly useful in locations near the water. A concentrated seaweed extract can also be used to make liquid fertiliser. The ability of the organism to restore nitrogen levels already present in the soil is one of the reasons why this sort of fertiliser is so popular.


Due to excessive levels of alkalinity in the soil in many nations, such as India, lands that historically generated great agricultural yields can no longer be exploited. The ph level must be lowered and the soil’s ability to hold onto water improved in order for crops to be grown on these fields, which are sometimes referred to as “Usar” lands.

Further Readings