But what exactly are algae? Algae is the name given to a large and diverse group of oxygenic, phototrophic, eukaryotic microorganisms. Algae are eukaryotic, which means they have a nucleus. This differentiates them from bacteria and photosynthetic Cyanobacteria. They are oxygenic phototrophs, meaning they use light as their energy source for growth and produce oxygen as a byproduct, like plants.
But what distinguishes algae from plants is that algae do not have any tissue differentiation. Plants can differentiate their tissues into roots, trunks, and leaves, all very different tissue types. In contrast, algae are composed of cells that are generally all the same.