Algae are classified as part of the kingdom Plantae, but they are often given their own separate classification within the kingdom called Protista. While algae share some characteristics with plants, such as the ability to perform photosynthesis, they are significantly different in structure and complexity.
Algae can be found in various environments and range from unicellular forms, like diatoms and dinoflagellates, to multicellular forms, such as seaweeds. Their classification can be complex due to their diverse forms and habitats, leading scientists to sometimes categorize them under both Plantae and Protista.
In summary, while they are related to the plant kingdom, algae have unique features that warrant a distinct classification within the broader context of biological taxonomy.