Algae exist in environments ranging from oceans, rivers, and lakes to ponds, brackish waters and even snow. Algae are usually green, but they can be found in a variety of different colors. For instance, algae living in snow contain carotenoid pigments in addition to chlorophyll, hence giving the surrounding snow a distinctive red hue.

Algae are defined as a group of predominantly aquatic, photosynthetic, and nucleus-bearing organisms that lack the true roots, stems, leaves, and specialized multicellular reproductive structures of plants. It is animportant group of Thallophyta (Thallos — a sprout; phyton — a plant), the primitive and simplest division of the plant kingdom. The orderly systematic study of algae is called Phycology. The algae are chlorophyllcontaining primitive plants, both prokaryotic and eukaryotic, starting from unicellular to multicellular organisations. Multicellular forms of algae include the giant kelp and brown algae. Unicellular forms include diatoms, euglenophyta and dinoflagellates.

Characteristics of Algae

The general characteristics of algae are common to plants as well as animals. For instance, algae can photosynthesize like plants, and they possess specialized structures and cell-organelles, like centrioles and flagella, found only in animals. Listed below are some of the general characteristics of algae.

• Algae are photosynthetic organisms.
• Algae can be either unicellular or multicellular.
• Algae lack a well-defined body, so, structures like roots, stems or leaves are absent.
• Algae are found where there is adequate moisture.
• Reproduction in algae occurs in both asexual and sexual forms. Asexual reproduction occurs by spore formation.
• Algae are free-living, although some can form a symbiotic relationship with other organisms.

Classification of Algae

F.E. Fritsch (1935, 1945) in his book “The Structure and Reproduction of the Algae” proposed a system of classification of algae. He treated algae giving rank of division and divided it into 11 classes. His classification of algae is mainly based upon characters of pigments, flagella and food reserve. Eleven classes proposed by Fritsch are as follows.

Class Chlorophyceae (Green Algae)

Class Xanthophyceae (Yellow Green Algae)

Class Chrysophyceae (Golden Algae)

Class Bacillariophyceae (Diatoms)

Class Cryptophyceae

Class Dinophyceae

Class Chloromonadineae

Class Euglenineae

Class Phaeophyceae (Brown Algae)

Class Rhodophyceae (Red Algae)

Class Cyanophyceae/Myxophyceae (Blue-Green Algae)