Red Algae

The thallus of multicellular algae is not differentiated into roots, stem and leaves. It may be in the form of filaments, sheets or colonial aggregate of cells. The filaments and sheets are always connected to the substratum with the support of holdfast. Some algae are complex and very long measuring in length. There are three different types of algae present – Red algae (Rhodophyceae), Brown algae (Phaeophyceae) and Green algae (Chlorophyceae). 

Red Algae (Rhodophyceae) 

The members of Rhodophyceae are called Red Algae because of the presence of red pigment r-phycoerythrin, which masks the green colour of chlorophyll a.

Traits of Red Algae

A few traits of red algae are discussed below – 

• Majority of Red Algae are marine, abundantly found in the warmer waters. Batrachospermum is a freshwater form seen in hill rivers and unicellular Porphyridium is terrestrial. 
• They occur both in well-lighted regions close to the surface of the water and at great depths in the ocean where little light penetrates. 
• The plant body may be unicellular, filamentous, parenchymatous sheets, ribbon-like or lace-like. 
• Cell wall consists of cellulose, pectin and some lipopolysaccharide which is called phycocolloids. 
• Some red algae are coralline. They secrete and deposit calcium carbonate over their walls and form coral-like structures. Example – Corallina.
• The cytoplasm of red algal cells bears coloured plastids, called chromatophores. 
• The photosynthetic pigments found in the chromatophores are chlorophyll a, chlorophyll d, alpha-beta carotenes, xanthophylls and biliproteins. 
• The biliproteins or phycobilins are water-soluble pigments located in phycobilisomes. 
• There are two types of biliprotein –
• r-phycoerythrin i.e., red in colour
• r-phycocyanin i.e., blue in colour

Phycobilins are the exact pigments that are seen in cyanobacteria.

• Red algae are photoautotrophic, but some others are colourless and live as parasites on other photosynthetic red algae. Example – Harveyella 
• Reserve food is in the form of floridean starch. 
• Vegetative reproduction takes place by fragmentation.
• Asexual reproduction takes place by no motile spores such as monopores, neutral spores, carpospores, tetraspores. 
• Sexual reproduction is an oogamous type. Male sex organs are spermatogonia or antheridia, and female sex organs are carpogonia. Male gametes are motile and they are called spermatia. 
• Each carpogonium is flask-shaped and remains attached to the plant body. It comprises an egg nucleus in its swollen core. Carpogonium maintains an extended receptive outgrowth called trichogyne. 
• Spermatia are carried by water currents to the trichogyne to affect fertilisation. 
• The zygote may undergo meiosis to produce haploid spores or produce a diploid sporophyte by mitosis called carposporophyte. 
• Life cycle has an alternation of haploid and diploid multicellular generations.

Few common red algae

Polysiphonia 

Polysiphonia is a little, vertical and bushy marine alga found along the Atlantic and Pacific coasts. A few species exist as epiphytes on mangroves or brown seaweeds. The plant body is promptly fixed to the substratum. It carries two types of branches:-

• Dwarf
• Long

Dwarf branches are called trichoblasts. These include sex organs, antheridia on male plants and archegonia on female plants. After fertilisation, a diploid carposporophyte is formed which leads to diploid carpospores. On germination, each carpospore forms a tetrasporophyte. This corresponds to the gametophytic plant body and propagates tetraspores. Each tetraspore germinated to develop a gametophytic plant. 

Polysiphonia is a source of bromine.

 Gracilaria 

Gracilaria is an agar-yielding red alga i.e., agarophyte, seen growing in lagoons near seashores. Its thallus is highly branched, cylindrical with a cartilaginous texture. Sexes are separate. Male plants develop spermatia. Female plants bear carpogonium branches. These on fertilisation, form cystocarps which bear carpospores. Every carpospore on germination forms the gametophytic plant body.

Importance of Red Algae

• Extracts from Corallina are used for the treatment of kidneys, bladder and lung diseases. 
• Calcareous red algae play an important role in the formation of so-called coral reels. 
• It is a kind of glue that is obtained from Gloiopeltis. It is used as an adhesive and in sizing textiles, paper, etc.
• 4. Rhodomella and Polysiphonia are used to obtain bromine of commercial importance. 
• Some red algae are cultivated as food. Porphyra is grown in shallow seawater in Japan and China.

Conclusion

Algae can be classified as plants which are without an embryo and Embryophyta which are plants with embryos. The word algae were formed by Linnaeus for seaweeds and are distributed all over the world.  Some algae are complex and very long in length. There are basically three types of algae which are Red algae, Brown algae and Green algae.