Algae possess diverse characters in their pigments, nature of reserve food, nature of cilia etc. According to these morphological and physiological differences they are classified by many people. Fritsch (1935) classified the whole of the algae into eleven classes on the basis of type of pigments, nature of reserve food material, mode of reproduction etc.
Smith classified algae into seven divisions. These divisions include one or more classes. The divisions and classes are the following.
1. Chlorophyta: Chlorophyceae and Charophyceae
2. Chrysophyta: Chrysophyceae, Xanthophyceae and Bacillariophyceae
3. Pyrophyta: Dinophyceae and Desmophyceae
Smith included certain algae of uncertain position into Chloromonadales and Cryptophyceae