In this article, we will learn about different types of algae and their characters such as; Chlorophyceae (Green algae), Phaeophyceae (Brown Algae), Rhodophyceae (Red Algae), Xanthophyceae (Yellow-Green Algae), Chrysophyceae (Golden Algae), Bacillariophyceae (Diatoms), Cryptophyceae, Dinophyceae, Chloromonadineae, Euglenineae, and Cyanophyceae or Myxophyceae (Blue-green algae).
What is Algae?
- Algae mainly found in aquatic environments, they are protists that contain plant-like characteristics.
- Some examples of algae are Pond scum, seaweed, and giant kelp.
- Algae are eukaryotic organisms and are capable of photosynthesis because they contain chloroplasts like plants.
- Some algae contain flagella, centrioles like animals and they can feed on organic material in their habitat.
- The size of algae is variable, ranges from a single cell to a very large multicellular species, and they can be found in saltwater, freshwater, wet soil, or on moist rocks.
- Unlike higher plants and angiosperms, algae do not contain any roots, stems, leaves, or flowers and they also lack vascular tissue.
- Algae are the primary producer in aquatic environments, they serve as the food source of different marine organisms such as brine shrimp and krill, etc.
- They reproduce by both sexually, asexually or by combining both processes through alternation of generations.
- Those algae are followed the asexual reproduction, they naturally divides or produce motile or non-motile spores.
- Those algae are followed the sexual reproduction, they produce gametes under some certain environmental stimuli – such as temperature, salinity, and nutrients – become unfavorable.
Types of Algae
F.E. Fritsch divides the algae into 11 classes in his book “Structure & reproduction of algae”. He classified algae on the basis of their pigmentation, thallus-structure, reserve food, flagellation & modes of reproduction.
1. Chlorophyceae (Green algae)
- There are about 7000 known species of Chlorophyceae. Most of them lived in freshwater except a few (- 10%) marine forms.
- They can be single-celled (Chlamydomonas), colonial (Volvox), filamentous (Spirogyra) and tubular forms (Caulerpa).
- They are capable of photosynthesis because of chloroplast, which contains different photosynthetic pigments such as Chl- a, b, carotenes, and xanthophylls.
- Their color varies from yellowish-green to dark green.
- They possess mitochondria with flat cristae.
- They possess a central vacuole and cell wall that is composed of cellulose and pectin.
- Green algae reserve their food in the form of starch and sometimes fat frequently aggregates around the pyrenoids.
- Some species of Green algae possess one or two flagella.
- They follow both asexual and sexual reproduction. The sexual reproductions are isogamous, anisogamous, and oogamous.
- Some of them develop non-motile aplanospores, while others produce zoospores with one flagellum
Example: Spirogyra, Ulothrix, Caulerpa, VoIvox, Acetabularia, Chlorella etc.
2. Phaeophyceae (Brown Algae)
- There are 2000 species under Phaeophyceae most of them live in marine water.
- In Phaeophyceae the Unicellular forms are absent.
- They possess a huge amount of brown colored xanthophyll pigments known as fucoxanthin (C40H56O6), that’s why they appear in brown color.
- They have photosynthetic pigments such as Chl-a, c, carotenes &xanthophylls.
- The thallus plant body is differentiated into holdfast, stipe and lamina (blade or frond). The lamina is annual while stipe is perennial, and holdfast helps in anchorage.
- The kelps or seaweeds are the larger form of brown algae such as Macrocystis (30-60m, the largest sea plant), Nereocystis (20-30m.). For buoyancy, giant kelps possess air vesicles or bladder.
- They possess a cell wall, which is made up of polysaccharides like cellulose, pectose and algin (non- sulphated phycocolloids).
- The calcium salts of alginic acid (a major phycocolloid) known as algin. These Phycocolloids are complex polysaccharides that are reserved in the cell wall of algae, and protect them from desiccation and prevent drying or freezing (in winter) when exposed to air in low tide.
- Brown Algae contains anchoring organ, a stalk, photosynthetic organs, and reproductive tissues which develop spores and gametes.
- Brown Algae reserved their food in the form of laminarin and mannitol.
Example: Laminaria, Macrocystis, Nereocystis, Pelvetia, Sargassum, and Pelagophycus.
3. Rhodophyceae (Red Algae)
- There are about 5000 known species of Red Algae most of them are lived in marine except a few freshwater forms (Batrachospermum).
- Red Algae possess phycoerythrin (red pigment, C34H46O8N4) & phycocyanin (the blue pigment, C34H46O8N4) that’s why they appear in red color.
- In sea, they are considered as the deepest growing algae where other photosynthetic forms cannot grow.
- They can absorb the blue-green region of the spectrum i.e. 480-520 nm due to the presence of phycoerythrin (red pigment, C34H46O8N4) & phycocyanin (the blue pigment, C34H46O8N4), which can penetrate greater depth of water.
- Because of excess phycoerythrin, they appear more red in deep water, whereas in shallow water, they appear green due to the presence of more chlorophyll. This color change property of red algae is known as the chromatic adaptation (Gaidukov phenomenon).
- Most of them are photoautotrophs except few colorless & parasite such as Harveyella which live on other red algae.
- Their cell wall is made of cellulose, pectin & sulphated phycocolloids (agar, carageenin & funori).
- They reproduce by sexually, asexually, and by vegetative methods. The vegetative method in Red algae is followed by the fragmentation & regeneration of holdfast. The asexual reproduction in red algae is followed by spore formation where the sexual reproduction is by oogamous type.
- The thallus organization of algae may be unicellular (Porphyridium), filamentous (Batrachospermum, Polysiphonia), pseudofilamentous (Astocystis), parenchymatous (Porphyra), lace-like (Gelidium), ribbon-like (Chondrus) etc.
- Red Algae reserved their food in the form of floridean starch.
Example: Gonyostomum, Chattonella, Psammamonas, Heterosigma, Vacuolaria, and Psammamonas.
4. Xanthophyceae (Yellow-Green Algae)
- These are the least prolific species of algae. They have only 450 to 650 species.
- Yellow Green Algae are unicellular organisms.
- They possess a cell wall which is composed of cellulose and silica.
- For motion, they contain one or two flagella.
- They appear lighter in color due to the absence of certain pigments in their chloroplasts.
- Xanthophyceae usually form in small colonies of only a few cells.
- Most of the Yellow Green Algae lived in freshwater but some of them can be found in salt water and wet soil environments.
- The main pigments of Xanthophyceae include chlorophyll a and e, β-carotene and xanthophyll’s.
- The motile form of Xanthophyceae has two unequal flagella at the anterior, one tinsel and the other whiplash type.
- They reserve their food in the form of fat.
- In Xanthophyceae the sexual reproduction is rare and isogamous.
Example: Tribonema, Vaucheria, Botrydium and Bumilleriopsis.
5. Chrysophyceae (Golden Algae)
- These are unicellular, colonial flagellates comprising coccoid, capsid, filamentous, amoeboid, plasmodial and parenchymatous types.
- There are about 12,000 species of Chrysophyceae, most of them lived in freshwater and some of them found in salt water environments.
- Their main pigments are chlorophyll a, P-carotene and xanthophyll’s.
- Golden Algae reserve their food in the form of fat.
- Sexual reproduction is rare in Golden Algae.
- They endogenously produces a specialized resting cells known as cysts.
- The motile form of golden algae contains either one flagellum tinsel type or when two one tinsel and one whiplash type.
- Their cell wall is made up of pectin and silica.
Example: Chrysocapsa, Lagynion, Ochromonas, Chrysamoeba.
6. Bacillariophyceae (Diatoms)
- These are known as Diatoms.
- Bacillariophyceae are unicellular or colonial.
- There are about 12,000 to 15,000 species of Bacillariophyceae.
- Under microscope the Diatoms appear as drum-shaped cells that are seldom present in chains.
- Their main pigments include chlorophyll a and c, β-carotene and xanthophyll’s.
- Diatoms reserve their food in the form of fat.
- In Bacillariophyceae sexual reproduction is of widespread occurrence.
- They contain a silicified cell wall, which is made up of pectin and silica.
- They can be found in freshwater, marine and terrestrial.
Example: Cyclotella, Thalassiosira, Navicula, Nitzschia.
- Cryptophyceae are Unicellular flagellated forms and scantly represented groups.
- There are about 200 species of Cryptophyceae.
- Under the light microscope Cryptophyceae appear as comma-shaped and look red or similar colors.
- Cryptophyceae reserve their food in the form of starch.
- The cell wall is made up of cellulose.
- Cryptophyceae possess two unequal flagella.
- Sexual reproduction is rare and isogamous in Cryptophyceae.
- Cryptophyceae is lived in both fresh water and marine water.
Example: Plagioselmis, Falcomonas, Rhinomonas, Teleaulax, and Chilomonas.
- Dinophyceae are motile, unicellular organisms.
- Their main pigments are chlorophyll a and c, β-carotene and xanthophyll’s.
- Sexual reproduction is rare and isogamous in Dinophyceae.
- Most of Dinophyceae lived in marine water and few are fresh water.
- Dinophyceae reserve their food in the form of starch or fat.
Example: Alexandrium, Dinophysis, Gymnodinium, Peridinium, Polykrikos, Noctiluca, Ceratium, Gonyaulax.
- These are Unicellular.
- The chromatophore is bright green with an excess of xanthophyll’s.
- Chloromonadineae reserve their food in the form fat.
- The motile form of Chloromonadineae is biflagellate.
- They only live in freshwater.
- These are motile unicellular or colonial organisms.
- Euglenineae contain photosynthetic pigments such as chlorophyll a and b, β-carotenes, xanthophyll.
- Euglenineae reserve their food in the form of starch or fat.
- They contain naked ciliated reproductive organs that’s why Euglenineae are resemble microscopic animal.
- Sexual reproduction in Euglenineae is not proved definitively.
- The Cell wall is absent in Euglenineae.
- They contain one or sometimes more flagella, tinsel type, hence they are motile.
11. Cyanophyceae or Myxophyceae (Blue-green algae)
- These are unicellular, colonial or multicellular bodies.
- Their nucleus is prokaryotic.
- The mitochondrial and chloroplast is double membraned.
- Blue-green algae contains different types of pigments such as chlorophyll-a, β-carotene, xanthophyll’s and phycobilins, c-phycoerythrin and c-phycocyanin. The blue color occurs due to the presence of phycocyanin pigment.
- There is no motile stage in Cyanophyceae.
- Cyanophyceae reserve food in the form of cyanophycean or myxophycean starch.
- The cell wall of Cyanophyceae is made up of pectin or cellulose.
- Many Blue-green algae show ‘false’ branching and special types of cells called ‘heterocyst’s’.
- Sexual reproduction is absent in Cyanophyceae.
- They are ubiquitous, and can be found everywhere.
Examples: Nostoc, Oscillatoria, Anahaena, Lyngbya, Plectonema.
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