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Physoderma
''Physoderma'' is a genus of chytrid fungi. Described by German botanist Karl Friedrich Wilhelm Wallroth in 1833, the genus contains some species that are parasitic on vascular plants, including ''P. alfalfae'' and ''P. maydis'', causative agents of crown wart of alfalfa and brown spot of corn, respectively.〔 Of the chytrid genera, ''Physoderma'' is the oldest.〔Sparrow FK. 1960. Aquatic phycomycetes. 2nd ed. Ann Arbor, Michigan: University of Michigan Press.〕 However, species were confused with the rust fungi, the genus ''Synchytrium'', and the genus ''Protomyces'' of Ascomycota.〔Karling, J.S. 1977. Chytridiomycetarum Iconographia. Monticello, New York: Lubrecht & Cramer.〕 Members of ''Physoderma'' are obligate parasites of pteridophytes and angiosperms.〔 There are approximately 80 species within this genus (depending on whether one includes those traditionally belonging to ''Urophlyctis'').〔
==Taxonomic History==
The genus was erected in 1833 on the basis of resting spore development 〔〔 and included 6 species.〔Karling, J.S. 1950. The genus ''Physoderma'' (Chytridiales). Llyodia. 13(1): 29.〕 Unfortunately, his original diagnosis was very similar to that of ''Protomyces'', which lead others to place species in the wrong genus. In 1877, Nowakowski erected the genus ''Cladochytrium'' in the Chytridiales, which lead to the transfer of ''Physoderma'' to the Chytridiales as well 〔 by Schroeter in 1883.〔 Just prior to that (1882), Schroeter added an additional 4 species to the genus and noted, for the first time, epibiotic, ephemeral zoosporangia. He also claimed that sexual reproduction was through the of fusion of two cells and resulted in the resting spores. In 1889, Schroeter created the genus ''Urophlyctis'' for those species with epibiotic, ephemeral zoosporangia and sexually derived resting spores. He placed both in the same subfamily as ''Cladochytrium''. In 1891, Fischer refuted Schroeter's observations on sexual reproduction and merged ''Physoderma'' and ''Urophlyctis'' with ''Cladochytrium''. In 1897, Schroeter separated them once more. Magnus, in 1901, used characteristics of the resting spore and host plant reaction to distinguish between ''Physoderma'' and ''Urophlyctis''. He claimed that resting spores from ''Physoderma'' were globose and ellipsoidal, and those from ''Urophlyctis'' were flattened on one side. ''Physoderma'' species cause discoloration and slight malformation, while ''Urophlycits'' cause significant malformation and hypertrophy. Sparrow, in numerous publications, expressed concerns over the characters used to distinguish the two genera.〔 In 1943, Sparrow suggested that the genus be merged with ''Urophlyctis'', which was done by Karling in 1950.〔〔 He also moved ''Physoderma'' to its own family, the Physodermataceae.〔 Sparrow, in 1962, decided the genera were distinct based on morphology and host reaction. However, at this time, the two genera are considered synonymous.〔Porter TM, W Martin, TY James, JE Longcore, FH Gleason, PH Adler, PM Letcher, & R Vilgalys. 2011. Molecular phylogeny of the ''Blastocladiomycota'' (Fungi) based on nuclear ribosomal DNA. Fungal Biology 115: 381-392.〕 Typically, it was thought that ''Physoderma'' was related to the polycentric genera ''Cladochytrium'' and ''Nowakowskiella''〔〔 Based on the ultrastructure of the zoospore, it was realized that ''Physoderma'' belongs to the Blastocladiales,〔 which later became the Blastocladiomycota. Recent phylogenetic analyses indicate that ''Physoderma'' and ''Urophlycits'' might be separate genera.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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