History

The plasmodiophores have historically been regarded as Fungi. The first description of plasmodiophores as a taxonomic group was in 1885 by Zopf, who united two genera Plasmodiophora and Tetramyxa in a common family “Plasmodiophoreæ”, inside the group “Monadineæ”, as part of the division Myxomycetes. The family was renamed “Plasmodiophoraceae” in 1888 by Berlese.^[9] In 1892, Engler placed the family in its own class “Plasmodiophorales”, later renamed “Plasmodiophoromycetes” to fit nomenclature standards.^[10]

In 1969 Whittaker, in his five-kingdom system, elevated the group to a separate phylum “Plasmodiophoromycota”, acknowledging them as protists instead of fungi.^[1]

In 1993 Cavalier-Smith included the plasmodiophores and their sister group Phagomyxida in their current class, Phytomyxea, as part of a polyphyletic phylum called Opalozoa, which at the time contained a diverse assemblage of unrelated zooflagellates, opalines and proteomyxids.^[11] Eventually this phylum was discarded, and the name Opalozoa was modified to label a group inside the phylum Bigyra containing the opalines, bicosoecids and related organisms.^[12]

Finally, after phylogenetic analyses, in 2002 Cavalier-Smith placed all Phytomyxea, including plasmodiophores, in the subphylum Endomyxa, inside the rhizarian phylum Cercozoa.^[13][14]

Classification

The number of genera varies between sources. There are three accepted genera in the group according to the WoRMS register: Plasmodiophora, Spongospora and Tetramyxa.^[15] Below is a complete list with genera that are not included in the register but appear in relevant sources:^[3][16][17]

• Ligniera R. Maire & A. Tison 1911 (=Anisomyxa Nemec 1913; Rhizomyxa Borzí 1884; Sorolpidium B. Nĕmec 1911)
• Membranosorus C.H. Ostenfeld & H.E. Petersen 1930
• Octomyxa J.N. Couch J. Leitner & A. Whiffen 1939
• Polymyxa G.A. Ledingham 1939
• Plasmodiophora Woronin 1877 (=Ostenfeldiella Ferdinandsen & Winge 1914)
• Sorodiscus G. Lagerheim & Ø. Winge 1912
• Sorosphaerula J. Schröt. 1886 (as Sorosphaera) nom. nov. Neuhauser & Kirchmair 2011^[18] (=Tuburcinia E.M. Fries; Sorosporium F. Rudolphi 1829)
• Spongospora Brunch. 1887 (=Clathrosorus C. Ferdinandson & Ö. Winge 1920)
• Tetramyxa K. Goebel 1884 (=Molliardia R. Maire & A. Tison 1911; Thecaphora W. A. Setchell 1924)
• Woronina Cornu 1872

These genera were once considered plasmodiophores^[19] until they were excluded:^[17]

• Cystospora J.E. Elliott 1916 – possibly a physiological symptom.
• Frankiella Maire & A. Tison 1909 – synonym of the bacteria Frankia.
• Peltomyces L. Léger 1909 – excluded as unclassifiable.
• Pyrrhosorus H. O. Juel 1901 – considered Labyrinthulida incertae sedis.^[20]
• Sporomyxa L. Léger 1907 – excluded as unclassifiable.
• Trematophlyctis Patouillard 1918 – a chytrid fungus.^[21]