Red Algae: Rhodophyta, Classification, Morphology, Types

Red algae or Rhodophyceae are called so due to the presence of a red pigment called r-phycoerythrin. Most of these species are marine and mostly found in warmer areas. The red thallus of most red algae is multicellular while some have complex organisation. Their food storage is in the form of floridean starch, which is similar in structure to amylopectin and glycogen. Example: Gracilaria, Gelidium, Porphyra, Polysiphonia.

Also read: Green Algae

Key Terms: Organism, Species, Pigment, algae, habitat, eukaryotes.

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What are Algae?

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An algae (singular) is referred to as a living, eukaryotic, and photosynthetic organism that is usually grown in moist areas. Hence, they are called members of aquatic organisms. Like plants, these organisms also absorb chlorophyll and other biological pigments that act as a primary colouring agent and also help in absorbing energy from light.

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Types of Algae

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Algae are grouped under Kingdom Protista. Furthermore, they are classified into seven different types:

• Pyrrophyta
• Euglenophyta
• Rhodophyta/ Red Algae
• Phaeophyta/ Brown Algae
• Chlorophyta/ Green Algae
• Xanthophyta/ Yellow-Green Algae
• Chrysophyceae/ Golden-brown Algae

  Types of Algae: (a) Green algae (i) Volvox (ii) Ulothrix  (b) Brown algae (i) Laminaria (ii) Fucus (iii) Dictyota (c) Red algae (i) Porphyra (ii) Polysiphonia

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Red Algae or Rhodophyta

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Red Algae, whose scientific name is Rhodophyta, belong to Class Rhodophyceae. There are mainly two classes of red algal namely the Florideophyceae and Bangiophyceae. Both Florideophyceae and Bangiophyceae constitute 99% of red algal diversity in marine and freshwater habitats.

Red algae or Rhodophyta is a distinctive type of species that is mainly found in freshwater lakes. They are the oldest type of eukaryotic algae and are red in colour due to the presence of a pigment called chlorophyll A, phycocyanin, and phycoerythrin. They are members of the tribe Amansieae (Rhodomelaceae, Ceramiales, Rhodophyta), wherein only Aneurianna and Lenormandia Sonder have foliar blades. They are a distinctive type of species, mostly found in deep freshwater bodies.

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General Characteristics of Red Algae

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Red algae are different from other groups apart from diatoms. The general characteristics of Red Algae are as follows:

• It lacks flagella and centrioles
• It contains photosynthetic pigments: chlorophyll a, d, alpha and beta carotenes, xanthophylls and biliproteins: r-phyocerythrin and r-phycocyanin. They are red and blue in colour respectively.
• It is found both in marine habitats as well as freshwater
• Multicellular, filamentous, blade structure
• Food is stored in the form of starch and polymers of galactan sulphate
• A pit connection between two algal cells
• Mode of nutrition is saprophytic, parasitic or also epiphytic.
• Cell wall consists of cellulose and different types of carbohydrates
• They can be found growing on solid surfaces or attached to other algae.
• Cytoplasm has coloured plastids called chromatophores.
• Some Red Algae are coralline: Secrete and deposit calcium carbonate.

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Structure of Red Algae

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The structure of red algae is:

• Cell walls of red algae are doubled.
• Agarise and Agaropectin removed as agar are found in outer layers.
• Celulose is abundant on the inside walls.
• Lack of flagella and centrioles
• Rhodophyceae contain spindle fibres, microtubules, photosynthetic membranes, but lack chloroplast endoplasmic reticulum

 

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Reproduction of Red Algae

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Red Algae reproduces both asexually and sexually. Asexual reproduction is conducted via spore formation and vegetative reproduction.

Sexual Reproduction: Red Algae sperm are not motile, therefore they have to rely on water currents for the transfer of games to the female although their sperm can glide to the trichogyne of a carpogonium.

• Trichogyne will continue to grow until it contacts a spermatium. After fertilisation, the cell wall thickens and isolates itself from the rest.
• Spermatium and carpogonium walls disintegrate on collision.
• Male nucleus splits and enters the carpogonium, while one half merges with the nucleus of the carpogonium.
• Polyamine spermine is generated.

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Common Red Algae

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Common Red Algaes found in nature are:

Polysiphonia

It is a little, vertical and bushy marine alga found along the Atlantic and Pacific coasts. Some species exist as epiphytes on mangroves or brown seaweeds. Its plant body is fixed to the substratum. It has dwarf and long branches.

Dwarf branches are called trichoblasts, which includes sex organs, antheridia, and archegonia. After fertilization, a diploid carposporophyte is formed which in turn forms diploid carpospores. After germination, each carpospore forms a tetrasporophyte. Each tetraspore germinates to develop a gametophytic plant.

Gracilaria

It is an agar-yielding red alga that grows in lagoons. The thallus is highly branched, cylindrical that has a cartilaginous texture.

Its sexes are separate. Male plants develop spermatia. Female plants bear carpogonium branches. On fertilization form cystocarps which have carpospores. Every carpospore forms the gametophytic plant body.

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Uses of Red Algae

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Red Algae have great ecological importance because they form a vital part of the food chain. Moreover, they are also involved in producing about 40 to 60 percent of the total global oxygen for aquatic habitats. The ecological and commercial importance of red algae are:

• Source of food for fishes and other aquatic animals
• Most important commercial food in Japan and the North Atlantic region.
• Agar is a jelly-like substance used in puddings, dairy and other food products.
• It is used as a source of food rich in vitamins, minerals and a rich source of calcium, magnesium, and antioxidants.
• They are good sources of dietary fibre as they promote healthy circulation, lower bad cholesterol and regulate blood sugar levels.
• They also nourish the skin, boost the immune system and help improve bone health.

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