Taxonomy and phylogeny of Irpicaceae and Meruliaceae (Polyporales, Basidiomycota) with descriptions of four new species from southwestern China.

Wood-decaying fungi play crucial roles as decomposers in forest ecosystems. In this study, four new wood-inhabiting fungi from Yunnan Province of southwest China-, , , and -are described and illustrated based on morphological and molecular evidence. The species is characterized by its slightly pink to orange basidiomata when dry, a monomitic hyphal system with simple septa, and narrowly ellipsoid basidiospores measuring 3.7-4.4 × 1.9-2.8 µm. The taxon is characterized by its hard, membranous, slightly yellow to yellow basidiomata; a monomitic hyphal system with simple-septate generative hyphae; and ellipsoid basidiospores measuring 3.8-6 × 2.6-3.7 µm. The species is characterized by its membranaceous, slightly gray to pale brown basidiomata; a monomitic hyphal system with simple-septate generative hyphae; and ellipsoid basidiospores measuring 4.3-6.2 × 2.2-3.3 µm. Additionally, the taxon is characterized by its coriaceous, pale cream to buff basidiomata; a monomitic hyphal system with simple-septate generative hyphae; and ellipsoid basidiospores measuring 2.8-3.5 × 1.4-2 µm. Sequences of the internal transcribed spacer region (ITS), the large subunit nuclear ribosomal RNA gene (nLSU), the translation elongation factor 1-α gene (TEF1), the largest subunit of RNA polymerase II (RPB1), and the second subunit of RNA polymerase II (RPB2) of the studied samples were employed, and phylogenetic analyses were performed using maximum likelihood, maximum parsimony, and Bayesian inference methods, ensuring the robustness of the findings. Based on the combined ITS + nLSU + RPB1 + RPB2 + TEF1 dataset, phylogenies of the two families Irpicaceae and Meruliaceae were constructed. In these analyses, was recovered as sister to ; as sister to ; as closely related to and ; and the new species as sister to .