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Phaeophyceae – Overview, Characteristics, Importance, Examples

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R.H. Whittaker categorized living things using the Five Kingdoms system. He divided living things into different categories according to their cellular makeup, mode of nourishment, bodily shape, reproductive ability, phylogenetic relationship, Protista, Planta, monera, and Animalia, and the fungi were the names of these five kingdoms.


Algae are primarily aquatic, having pigment- chlorophyll would be simple, thalloid and these creatures would be autotrophic in nature. They can be found in soils, damp stones, timber, and other environments. Few people establish relationships with lichen and animals. Vegetative, asexual, and sexual means of reproduction. Different kinds of spores, most frequently zoospores, are produced during asexual reproduction. Fragmentation is the method used in vegetative reproduction. Two gametes fuse together during sexual reproduction. These gametes can be similarly sized flagellated gametes, like Ulothrix, or they can be similarly sized non-flagellated (non-motile) gametes (as in Spirogyra). Isogamous reproduction is this type. Three major categories of algae are distinguished: Phyceae, Rhodophyceae, and Chlorophyceae

Brown algae



The class Phaeophyceae includes a group of algae known as brown algae. Their colour, which ranges from would be in the colour of dark or light brown to green which is olive, inspired their names. The majority of their habitats are maritime. The size and shape of the approximately a thousand five hundred species of Phaeophyceae vary widely. They have many cells, and the proportion of fucoxanthin to chlorophyll determines their color. They contain seaweeds, with Ectocarpus, Fucus, huge kelps, Sargassum, etc. as some famous examples.


  • Brown algae are primarily marine in habitat. They are located on chilly coastal seas. Either they are found floating freely or adhered to the substrate. Sargassum is an illustration of a free-floating brown alga, and Fucus is found adhering to rocks.
  • Brown algae come in a wide range of sizes and shapes. They can be as big as 100 metres or a few centimetres. Ectocarpus is a straightforward filamentous alga, while giant kelp can grow to a height of 100 metres. Great biodiversity can be found in kelp forests.
  • They have a multicellular algae structure. They have branches and filaments. Since there are no genuine roots, stems, or leaves, the plant’s body is a thallus.
  • They are anchored to their substrate by a holdfast, a root-like structure. Distinct species’ holdfasts have different structures. Like the roots of plants, they do not participate in the uptake of nutrients or water. They stop the water current from carrying algae away.
  • There is a tiny stalk, more of a stem, present. It’s known as a stipe. In the septate region, the fucus exhibits three unique layers: the pith (core region), cortex, and outer epidermis. Stipe can be either elastic or rigid. The hollow septate centre aids in the buoyancy of the algae.
  • The lamina, blade, or frond, which is a flattened structure on them, resembles leaves. The lamina’s surface may be wrinkled or smooth.
  • Pneumatocysts, which are unique gas-filled bladders, are present in some brown algae. They are primarily found close to the lamina. It gives algae buoyancy and keeps the portion of the algae necessary for photosynthesis close to the surface.
  • The Wall of the cell is composed of two layers: an inner layer of cellulose that gives strength and an outside layer that is sticky and formed of algin.
  • They include chlorophylls “a” and “c” and they are autotrophic. They also include xanthophyll and carotenoids.
  • Pyrenoids are not typically found in chloroplasts, however certain species do.
  • The primary xanthophyll pigment, fucoxanthin (C42H58O6), gives these plants their distinctive colour.
  • Complex carbohydrates, such as mannitol or laminarin, are used to preserve food.
  • A glucose polysaccharide is a laminarin. It would be a  polymer containing (branching) links at positions 1 and 3.
  • Sugar alcohol known as mannitol functions as an osmoprotectant and antioxidant, in addition to storing carbon. It safeguards them in their hostile environment.


  • They can reproduce sexually or asexually.
  • Plants reproduce through fragmentation.
  • Motile zoospores are produced during asexual reproduction. They feature two uneven flagella and a pear-shaped form.
  • Motile gametes, which seem to be likewise biflagellate and have two laterally connected flagella, are formed during sexual reproduction.
  • Oogamous, isogamous, or anisogamous sexual reproduction are all possible.
  • Gametes can combine in oogonium or water.


The ability of algae to repair carbon makes them significant. As primary producers, they play a significant role in the aquatic food chain. Numerous animals can be found in kelp forests. Laminaria, sargassum, and other edible seaweeds are only a few examples.

  • Commercially extracted alginic acid is utilized as a thickening agent in the food industry. In the baking sector, it serves as a stabilizer.
  • Batteries also utilise alginic acid.
  • Surgical threads and pills both include alginic acid.
  • As fertilisers, several species are employed.
  • Soda ash is created using kelp. It is employed in the manufacture of glass and soap.
  • Iodine-rich brown Laminaria has been used to treat iodine shortage conditions including goitre.
  • They have been utilised in medicine; sodium laminarin sulphate, for example, is an anticoagulant. Additionally, they have vermifuge and antibacterial effects.
  • Laminaria act as laxative.

Conceptual Question

Question 1: What is meant by soda ash?


Soda ash would be created by using kelp and this would play an essential role in glass manufacturing.

Question 2: Why is luminaria used in some medicine?


Iodine, a component required by the body to produce thyroid hormones, is present in luminaria. Additionally, potassium and iron are abundant in them. Luminaria is used as medicine by some despite major safety concerns.

Question 3: How does fucoxanthin act as coloring pigment?


By absorbing blue light and green light with a bandwidth of 450–540 nm, it gives algae a brownish–olive hue. Brown algae and the majority of other heterokonts have it as an additive pigment in their chloroplasts, which gives these a brown hue or the olive-green hue.

Question 4: Which chlorophyll is present?


Chlorophyll a and chlorophyll c would be present in the case of Phaeophyceae.

Question 5: Which would act as an osmoprotectant and why?


Mannitol is an Osmo protectant that is produced by a variety of plants and fungi. Mannitol is also a potent chelating agent of oxygen radicals (ROS). Mannitol is used by some phytopathogenic fungi to thwart ROS-mediated plant resistance.

Question 6: How does laminaria act as a laxative?


Luminaria is a variety of kelp. It might have antibacterial and antioxidant effects. Additionally, it has laxative properties. A dried bundle that has been compressed into a stick is known as a luminaria stick. A luminaria stick expands after being put into the vagina because it absorbs moisture. The cervix is gradually opened (dilated) by this.

Last Updated : 14 Jul, 2022
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