Algae belongs to four different kingdoms, including the kingdom bacteria, kingdom plantae, kingdom protista and kingdom chromista. The classification of algae depends on its features.
Algae is a collective term for many organisms, so it is classified into different kingdoms. The majority of algae are plants, so they are in the kingdom plantae. They produce their own chlorophyll and use photosynthesis; however, they do not have roots or stems as regular plants do. There are approximately 36,000 different forms of algae known to man, and they can be found in fresh water and saltwater. Scientists believe that algae has been around in various forms for more than 12 million years.