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  • Last Updated : 04 Dec, 2022
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Algae, bryophytes, pteridophytes, gymnosperms, and angiosperms are all members of the plant kingdom. Algae are chlorophyll-containing, simple, thalloid, autotrophic, aquatic creatures. Algae are categorised into three groups based on the type of pigment they contain and the type of food they store. These groups are Chlorophyceae, Phaeophyceae, and Rhodophyceae.

Plant Kingdom Classification

Kingdom Plantae (Plant Kingdom) is divided into distinct divisions based on whether plants have a well-differentiated body, the existence or lack of specialised tissues for transport, and the ability to carry seeds. Each division’s characteristics and examples are shown below. aquatic creatures that are gently Algae are categorised into three groups based on the type of pigment they contain and the type of food they store. These groups are Chlorophyceae, Phaeophyceae, and Rhodophyceae.


While algae are plural, an alga is a singular form. The eukaryotic, living organism that is typically cultivated in damp environments is called an alga. As a result, they are referred to as aquatic organisms. These species, like plants, have chlorophyll and other biological pigments, which serve as a key colouring agent and aid in absorbing light energy.

Red Algae

The group of red algae known as Rhodophyta is one of the oldest eukaryotic algae groups. The bulk of species (6,793) is multicellular marine red algae, primarily belonging to the Florideophyceae (class), which also includes numerous well-known seaweeds.

Red algal seaweed is prevalent in freshwater, but it is abundant in coastal areas. Red algae in freshwater are present in amounts of about 5%, with warmer regions having higher concentrations. In the asexual class Cyanidiophyceae, there are no terrestrial species other than two coastal cave-dwelling species; this may be the result of an evolutionary bottleneck in which the last common ancestor lost around 25% of its core genes and much of its evolutionary plasticity.

Red Algae (Rhodophyceae)

The marine algae family Rhodophyceae, also known as “red algae,” is mostly red in colour and has a filamentous or membranous fundamental form. They are among the oldest families of eukaryotic algae and tend to appear at deeper depths than green algae (Chlorophyta). The food is stored as floridean starch, which has a structure nearly identical to that of amylopectin and glycogen.
They do not have flagella.

It is a vast category of algae that includes over 831 genera and over 5,250 species. They are usually referred to as red algae because of the presence of r-phycoerythrin, a water-soluble red pigment. The r-phycoerythrin, on the other hand, is present in adequate and full amounts to conceal the chlorophyll a, resulting in the distinctive red colouration. More than 98% of the members are marine, with the remainder growing in fresh water. 

The freshwater members thrive in both stagnant and moving water (e.g., Asterocystis, Compsopogon) (e.g., Lamanea, Thorea, Batrachospermum etc.). Marine species can dwell at higher depths (even up to 30-90 metres) than other members of other groups. They have a high level of parasitism and epiphytism. The parasitic members’ size and pigmentation are greatly reduced.

On Codium fragile, parasitic species like Ceramium condicola and Polysiphonia lanosa can be found. Rhodophyceae members that grow on other Rhodophyceae members include Rhodochorton, Ceratocolax, etc. The unicellular genus Porphyridium is terrestrial and grows best in moist soil. Some marine members, such as Rhodocorton, Corallina, and Bostrychia, grow in the intertidal zone, but this is not the case for most marine members.

Rhodophycae Plant Classification

Morphology of Red Algae

Red algae can range in morphology from being unicellular to having complex parenchymatous and non-parenchymatous thallus. Red algae have doubled cell walls. The outer layers contain the polysaccharides agarose and agaropectin, which can be extracted from cell walls by boiling as agar. The majority of the inside walls are made of cellulose. Additionally, their plastid genomes are the most gene-rich ones yet found.

Cell Structure

Red algae do not have centrioles and do not have flagella during their whole life cycle. Red algal cell structure is defined by the presence of normal spindle fibres, microtubules, unstacked photosynthetic membranes, phycobilin pigment granules, pit connections between cells, filamentous genera, and the lack of chloroplast endoplasmic reticulum.


The phycobilins (phycocyanobilin, phycoerythrobilin, phycourobilin, and phycobiliviolin), which are contained within phycobilisomes, give red algae their distinctive colour. In the chloroplast, thylakoids are evenly dispersed and ungrouped. Other pigments include lutein, zeaxanthin, a, and b-carotene, and chlorophyll. The double membrane of the chloroplast envelope encloses the chloroplast. The absence of grana and the attachment of phycobilisomes to the stromal surface of the thylakoid membrane are two further traits that set red algal chloroplasts apart from other types.

Pit Connections

Red algae can be identified by their pit connections and pit plugs, which develop during the cytokinesis process following mitosis. In red algae, cytokinesis is not present. In the majority of situations, the centre of the newly formed division is left with a small pore. The pit connection is created in the areas where the daughter cells are still in contact. Shortly after the pit connection is formed, a pit plug forms and is deposited in the wall gap that connects the cells, blocking cytoplasmic continuity. Cells that have a common parent cell form primary pit connections. Because apical development is the norm, the majority of red algal cells have two principal pit connections, one to each subsequent cell.

Storage Products

Among the most significant photosynthetic products are Floridoside (the main product), Disofloridoside, digeneaside, mannitol, sorbitol, dulcitol, and others. As a long-term storage product, floridean starch, which is analogous to amylopectin in land plants, is freely (scattered) deposited in the cytoplasm. The concentration of photosynthetic products is influenced by environmental variables such as pH, medium salinity, light intensity, dietary constraints, and others. As the salinity of the medium increases, the amount of floridoside produced grows, preventing water from leaving the algal cells.

Differences between Red Algae, Brown Algae and Green Agae

Red Algae

Brown Algae

Green Algae

1. Red algae may be found in freshwater, brackish water, and, most notably, saltwater.
2. They include photosynthetic pigments such as chlorophyll a, d, and phycoerythrin.
3. The food stored in them is floridean starch.
4. They are classified as algae in the Rhodophyceae family.
5. They do not have flagella.
6. Their cell wall is composed of cellulose, pectin, and poly sulphate esters.
1. Brown algae can be found in freshwater, brackish water, and saltwater (occasionally).
2. They include photosynthetic pigments like as chlorophyll a, c, and fucoxanthin.
3. Mannitol or laminarin is stored in food in them.
4. They are classified as algae of the Phaeophyceae family.
5. They have two uneven, lateral flagella.
6. They have cellulose and a pigment-aligned cell wall.

1. The majority of green algae are found in freshwater, frequently adhering to submerged rocks and wood or as scum on stagnant water.

2. Blue-green algae and cyanobacteria contain the green pigment ‘chlorophyll a.’

3. Starch is a food that has been stored.

4. Green algae are members of the Chlorophyta phylum.

5. They also have flagellar apparatus.

6. They have cellulose, hemicellulose, and pectin cell walls.

Characteristics of Rhodophyceae

  • More than 98% of the members are marine, and 20 species (according to the research) can thrive in freshwater. The individuals might develop as saprophytes, parasites, or epiphytes.
  • The plant body can be multicellular or unicellular (Porphyridium). The multicellular shape might be feathery (Polysiphonia), parenchymatous (Porphyra, Crinellia), pseudoparenchymatous (Helmin- thocladia), filamentous (Gonio- trichum), or ribbon-like (Chondrus).
  • In Schizophrenia, they may grow up to 2 metres, which is larger than brown algae (Phaeophyceae), but not as large.
  • There is no sign of the flagellated motile phases.
  • The cell wall is made up of an inner cellulose layer and an exterior pectic layer. Agar-agar and carrageenans make up the majority of the dry weight of the cell wall and are the main components of the mucilaginous substance of the outer layer.
  • Cytoplasmic connections are maintained by holes in the cell walls of multicellular species. The so-called plasmodesmata are these cytoplasmic strands.
  • The number of nuclei in a cell varies greatly across Rhodophyceae members. Cells of the subclass Bangioideae are uni­nucleate, but the majority of members of the subfamily Florideae are multinucleate, with Griffithsia having 3,000–4,000 nuclei.
  • The cells may only have one discoid and parietal chromatophore with pyrenoids (Bangioideae) or several of them (Florideae).
  • The pigments used in photosynthetic reactions include xanthophylls like teraxanthin, lutein, violaxanthin, zeaxanthin, and flavoxanthin as well as biliproteins like r-phycoerythrin and r-phycocyanin. The algae’s distinctive red colour is caused by a sufficient amount of r-phycoerythrin, which totally obscures the chlorophyll a. Teraxanthin is the dominant Xanthcphyll, while chlorophyll B is not present.
  • Mannoglycerate, floridi-side, and floridean starch are the reserve foods.
  • All three types of reproduction—vegetative, asexual, and sexual—are possible.
    • Only in the unicellular stage does vegetative reproduction occur.
    • The monospore, neutral spore, carpospore, bispore, and tetraspore are all forms of asexual reproduction.
    • Oogamous sexual reproduction has advanced forms.
      • Spermatangium is the name for the male genital organs. Each spermatangium, or spermatium, produces one non-flagellate male gamete.
      • Carpogonia or procarp are the names for the female sex organs. Trichogyne, which resembles a flask and has a long neck, are carpogonia.
  • With the aid of water circulation, the spermatium makes contact with the trichogyne during fertilisation.
  • The post-fertilization modifications in Rhodophyceae are quite complex. Their carposporophyte grows. Each carposporophyte develops into a carposporangium, which gives rise to a single carpospore.
  • The majority of Rhodophycean species exhibit biphasic or triphasic life cycles.

Economic Importance of Rhodophycae

Red algae are crucial for the environment. They are an essential link in the food chain and contribute between 40 and 60% of the world’s oxygen supply, which is used in both terrestrial and other aquatic settings. Several red algae’s ecological and commercial values are listed below.

  • Fish and other aquatic creatures may eat algae naturally.
  • The most significant commercial food in Japan and the North Atlantic area is red algae.
  • Red algae are used to make agar, also known as agar-agar, a jelly-like material that is used in puddings, dairy toppings, and other fast food products.
  • Due to their high vitamin and mineral content, as well as their abundance of calcium, magnesium, and antioxidants, red algae have been utilised as a food source for thousands of years.
  • They are sources of dietary fibre because they can cut bad cholesterol, improve circulation, and control blood sugar levels.
  • They support the health of your bones and skin, as well as your immune system and skin.

Examples of Rhodophyceae

Example of Rhodophyceae includes Gracilaria, Gelidium, Porphyra, and Polysiphonia.

FAQs on Rhodophycae

Question 1: Red algae: what are they?


Red algae, which include more than 6000 species, are the earliest class of eukaryotic algae. They belong to the phylum Rhodophyta and the kingdom Protista. They have chlorophyll and are able to produce their own nourishment through photosynthesis.

Question 2: How is the kingdom of plants categorised?


Classification of the plant kingdom: Based on their capacity to generate seeds, the plant world is split into two categories. These two categories are phanerogams (seedless plants) and cryptogams (seed-bearing plants). Thallophyta, Bryophyta, and Pteridophyta are examples of cryptogams. Gymnosperms and Angiosperms make up Phanerogams.

Question 3: Why is the genus Rhodophyceae known as red algae?


The body appears red because the red pigment r-phycoerythrin predominates in the algae. Rhodophyceae is the name for these red algae.

Question 4: What is a Rhodophyceae example?


Gracilaria, Gelidium, Porphyra, and Polysiphonia are a few examples of Rhodophyceae.

Question 5: What is Rhodophyceae’s primary pigment?


Laminarin is the food that is stored in Phaeophyceae, and chlorophyll a and b are the main pigments. C) In Rhodophyceae, floridean starch serves as the stored food, and chlorophyll a, d, and phycoerythrin are the main pigments.

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