ALGAE

Algae are aquatic plants. They can be unicellular (aggregated in colonies) or multicellular, whose body is made up of undifferentiated tissues (thallus). However, multicellular algae have developed rhizoids, with which they attach themselves to the substrate. Algae are the first plants to appear on Earth: multicellular algae probably derive from autotrophic unicellular protists that have not divided completely, giving rise to filamentous forms, initially simple, then branched and laminar. All algae are important primary producers in aquatic environments; some are also used by humans for various purposes.