Algae includes a very big group of very different organisms, each with its own scientific name. For example, the scientific name of green algae is Pediastrum boryanum. Prymnesium parvum is the scientific name for golden brown algae.
Algae are a part of the eukaryote domain. Scientific names include the genus and species of the organism, but algae do not all belong to one species, or even one genus. Algae include genera, such as Chlorella, which are unicellular or made up of only one cell. On the other hand, giant kelp, a large brown alga, belongs to a different genus that is multicellular, and can grow up to 50 meters in length.