New Country Records of Cortinarius, Pseudolaccaria, Volvariella and Gerhardtia (Agaricales) from Northeastern and Southwestern China

China harbors a diverse array of macrofungi, yet its fungal diversity remains inadequately documented, particularly in under-explored regions such as the temperate forests of the northeast and the subtropical highlands of the southwest. In this study, four agaric species are reported as new records for China based on morphological observations and multilocus phylogenetic analyses. Phylogenetic analyses of the internal transcribed spacer (ITS) and nuclear large subunit (nrLSU) ribosomal RNA gene regions confirmed their generic and species-level placements. Cortinarius infidus was collected from mixed coniferous and broadleaf forests in Liaoning Province, Pseudolaccaria fellea from Pine-dominated forests in Liaoning Province, Volvariella clavocystidiata from pine-dominated coniferous forests in Liaoning Province, and Gerhardtia borealis from mixed coniferous–broadleaf forests in Guizhou Province. Comprehensive macro and micromorphological descriptions, color photographs, line drawings, scanning electron micrographs, and comparisons with closely related taxa and original literature are provided to confirm these identifications. These findings contribute to a better understanding of the distribution patterns of these genera and expand the known fungal diversity of China.