Global diversity analysis of plant-associated <i>Pseudopithomyces</i> fungi reveals a new species producing the toxin associated with facial eczema in livestock: <i>Pseudopithomyces toxicarius sp. nov</i> .

Facial eczema (FE) in ruminants is associated with the fungal toxin sporidesmin that can cause significant mortality in grazing livestock. Incidences are particularly severe in New Zealand but are reported worldwide. The syndrome has historically been attributed to <i>Pithomyces chartarum</i>, a species transferred to <i>Pseudopithomyces</i> in 2015, but the classification of many other <i>Pithomyces</i> species remains unresolved. In this study we investigated the taxonomy of <i>Pseudopithomyces</i> using modern species concepts and clarified which species make sporidesmin. Fungal isolates were cultured from grass samples obtained from New Zealand farms and roadside collections in 2014-2022. International isolates, including all available types, and historic isolates deposited in the International Collection of Microorganisms from Plants (ICMP) were also evaluated. Phylogenetic analyses of the ITS region plus four concatenated protein coding genes distinguished 15 species in the genus. We describe <i>Pseudopithomyces toxicarius sp. nov.</i> as a novel sporidesmin producing species, most formerly identified as <i>Pse. chartarum</i>, with 80 % of isolates in this study able to produce the toxin. Two <i>Pithomyces</i> species are combined into <i>Pseudopithomyces</i> as <i>Pseudopithomyces cynodontis comb. nov</i>. and <i>Pseudopithomyces pavgii comb. nov</i>. We also place <i>Pseudopithomyces pandanicola</i> in synonymy with <i>Pseudopithomyces palmicola. Pithomyces terricola</i> is reclassified into the family <i>Longipedicellataceae</i> as <i>Pseudoxylomyces terricola comb. nov</i>. <i>Pseudopithomyces chartarum</i> was the only other species where sporidesmin was detected, but this was found in only one of 14 isolates we tested. The extent of sporidesmin synthesis in this genus remains to be determined due to the limited availability of strains for testing in other species. Analysis of single nucleotide polymorphisms from whole genome Illumina sequences of isolates from <i>Pse. toxicarius, Pse. chartarum</i> and <i>Pse. palmicola</i> revealed distinct genetic subclades within each species. Four species were detected in New Zealand. <i>Pseudopithomyces toxicarius</i> and <i>Pse. chartarum</i> were recovered from grass samples collected from the North and South Islands, <i>Pse. palmicola</i> ICMP 12878 was recovered once from pasture at a North Island research station in 1993, and <i>Pseudopithomyces</i> sp. 'gladiolus NZ', which is currently undescribed. No species were unique to New Zealand, suggesting widespread global distribution. <b>Taxonomic novelties: New species:</b> <i>Pseudopithomyces toxicarius</i> B.S. Weir, D. Lee, J.S. Sidhu, & C.R. Voisey. <b>New combinations:</b> <i>Pseudopithomyces cynodontis</i> (M.B. Ellis) B.S. Weir & D. Lee, <i>Pseudopithomyces pavgii</i> (V.R. Nath) B.S. Weir & D. Lee, <i>Pseudoxylomyces terricola</i> (Manohar. & P. Rama Rao) B.S. Weir & D. Lee. <b>Citation:</b> Weir BS, Sidhu JS, Brosnahan CL, Lee D, Maclean PH, Park D, Jauregui R, Johnson RD, Petterson ME, Williams AFR, Morse NR, Sprosen JM, Lim Y-W, Bridgeman BJ, Walker TJ, Kumar S, Mace WJ, Prakash S, Liu X, Hume DE, Couldrey C, Beever RE, Voisey CR (2025). Global diversity analysis of plant-associated <i>Pseudopithomyces</i> fungi reveals a new species producing the toxin associated with facial eczema in livestock: <i>Pseudopithomyces toxicarius sp. nov</i>. <i>Studies in Mycology</i> <b>112</b>: 39-73. doi: 10.3114/sim.2025.112.02.