Phaeophyceae, commonly known as brown algae, are a group of multicellular algae found mainly in marine environments. They are most abundant in cold coastal waters and include some of the largest seaweeds in the world. Their brown colour is due to the pigment fucoxanthin, which masks the green colour of chlorophyll. They contain seaweeds, with Ectocarpus, Fucus, huge kelps, Sargassum, etc., as some famous examples.
Characteristics of Phaeophyceae
- Brown algae are primarily marine in habitat. They are located on chilly coastal seas. They are either found floating freely or adhering 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.
- 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 outer layer that is sticky and formed of algin.
- They include chlorophylls “a” and “c”, and they are autotrophic. They also include xanthophyll and carotenoids.
- Complex carbohydrates, such as mannitol or laminarin, are used to preserve food.
- Sugar alcohol known as mannitol functions as an osmoprotectant and antioxidant, in addition to storing carbon. It safeguards them in their hostile environment.
Reproduction of Phaeophyceae
- Vegetative Reproduction: Occurs by fragmentation of the thallus.
- Asexual Reproduction: By biflagellate zoospores. Zoospores have two unequal flagella.
- Sexual Reproduction: May be isogamous, anisogamous, or oogamous. and Advanced forms show oogamous reproduction.
Importance of Phaeophyceae
The ability of algae to fix 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 utilised as a thickening agent in the food industry. In the baking sector, it serves as a stabiliser.
- 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-deficient 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 acts as a laxative.