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.

The genus is placed in the family Protosteliidae within the monotypic order Protosteliida, which is part of a larger group of amoebozoans known as Variosea.

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