Protostelium is a genus of protosteloid amoebozoans, i.e., amoebae capable of forming simple fruiting bodies composed of a stalk and a ball of spores. It contains numerous species, including P. aurantium, which was initially classified in a different genus Planoprotostelium. Phylogenetic analyses revealed that Planoprotostelium branches from within the genus Protostelium, making them synonyms.