Red Algae General Characteristics Notes

Rhodophyceae (Red Algae)

Rhodophyceae Definition: Rhodophyceae (Greek: ~rhodo= red; phyton=plant) are a non-flagellate, bright red-coloured group of marine algae.

The Rhodophyceae or red algae are red due to the presence of a water-soluble red pigment,r-phycoerythrin. This pigment masks the green colour of chlorophyll a, giving the characteristic red appearance They also contain a blue pigment, r-phycocyanin.

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Rhodophyceae Distribution: Most of the members of Rhodophyceae are marine. Generally, they are found in the warm regions of the sea. They are attached to the substratum (lithophytes), at the bottom of the sea (even below 600 metres). Several red algae are found in freshwater (for example Batrachospermum sp.,), and wet soil (i.e., Porphyridium sp.). Some of these members are also found as parasites or epiphytes.

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Rhodophyceae General Features

1. The plant body may be unicellular (Porphyridium sp.) or multicellular. The multicellular form may be filamentous (Goniotrichum sp.), parenchymatous (Porphyra sp.)pseudoparenchymatous (Helminthodadia sp.), feathery (Polysiphonia sp.) or ribbon-like (Chondrus sp.). They may attain a size up to 2 metres as in Schizymenia sp
2. The flagellated motile stages are totally absent
3. The cell wall consists of the outer pectin and an inner cellulose layer. The mucilaginous material of the outer layer mainly consists of agar-agar and carrageenans. These constitute a major portion of the dry weight of the cell wall.
4. In multicellular members of this group, the cell walls have pits, through which cytoplasmic connections are maintained. These cytoplasmic threads are called plasmodesmata.
5. The members of Rhodophyceae show variation in the number of nuclei in a cell. In the members of the subclass Bangioideae, cells are uninucleate, but in the members of the subclass Florideae, most of the members are multinucleate. The number of nuclei is 3,000-4,000 in Griffithsia sp.
6. The cells may have one chromatophore with a central pyrenoid (Bangioideae) or many discoid and parietal chromatophores with pyrenoids (Florideae).
7. The photosynthetic pigments are chlorophyll a, chlorophyll b, chlorophyll d, a and -carotenes, and xanthophylls. Along with these pigments, some phycobiliproteins are also present, such as r-phycoerythrin, r-phycocyanin and alpha phycocyanin.
8. The reserve food is Floridian alpha phycocyanin. starch. Other than this, galactosides, floridiside and mannoglycerate are also present in the cytoplasm.
9. Reproduction takes place by all three means vegetative, asexual and sexual. Vegetative reproduction takes place only in unicellular forms. Asexual reproduction takes place by monospores, neutral spores, carpospores, bispores, and tetraspores.
   Sexual reproduction is of advanced oogamous type. The male and female sex organs are called spermatangium and carpogonium respectively. The latter are flask-shaped with a long neck, called trichogyne. Non-motile, male gametes are produced within antheridia, called spermatia. The spermatia are carried away by the water current to the extended part of the carpogonium.
10. The sporophytic plants may develop certain structures called tetrasporangia within which tetraspores (any of the spores produced in a group of four) are produced.
11. The life cycle is haplobiontic or diplobiontic in nature.
12. The alternation of generations varies from isomorphic to heteromorphic (where two generations are morphologically dissimilar).

red algae

red algae rhodophyta

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Similarities between algae and fungi

1. Both are eukaryotic and unicellular or multicellular.
2. Both are thallophytic, i.e., the body is not differentiated into roots, shoots and leaves.
3. Both have cell walls.
4. Both do not have vascular tissue.
5. Both reproduce by vegetative, asexual or sexual means. The reproductive organs are unicellular. Asexual reproduction occurs by spores.

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