Members of Olpidium are zoosporic pathogens of plants, animals, fungi, and oomycetes.
[3][4] Olpidium species exist as spherical zoosporangia inside the cells of their host.
[4] Olpidium species infect a wide variety of plants, animals, protists, and fungi and are fairly common in aquatic and terrestrial ecosystems.
[6] Based on zoospore ultrastructure, Donald J. S. Barr moved the genus into Spizellomycetales[7] In studies using molecular phylogenetics, O. brassicae, O. virulentus, and O. bornovanus were found to cluster with members of the former Zygomycota not with members of Chytridiomycota.
One researcher, has elevated Olpidium to the level of phylum (Olpidiomycota) and split the genus into several genera.