Four new species of Cortinariaceae (Agaricales) from Northwestern China.

Introduction: Cortinariaceae, which belongs to the Agaricales order, is a globally recognized family, known for its high species diversity.

Methods: Eight internal transcribed spacer (ITS) and nuclear large ribosomal subunit (LSU) sequences were newly generated, and phylogenetic analyses were performed by combining ITS and LSU datasets. Four species were identified as forming four independent lineages with robust support in phylogenies based on both datasets.

Results: These new species in the taxa, , , , and from Northwestern China are described and illustrated based on morphological and molecular evidence. is characterized by a convex and brownish vinaceous pileus, generative hyphae with clamp connections, and ellipsoid basidiospores (8.5-10.6 μm × 5.4-6.8 μm); is characterized by a broadly umbonate and snuff brown pileus, generative hyphae with clamp connections, and broadly ellipsoid to subglobose basidiospores (7.4-8.5 μm × 6.2-7.3 μm); is characterized by a violaceous gray pileus, generative hyphae with clamp connections, and smaller basidiospores (7.5-9.7 μm × 5.6-7.8 μm); and is characterized by a small and apricot-orange pileus, generative hyphae with clamp connections, and fusiform basidiospores (10.0-12.7 μm × 5.6-6.8 μm).

Discussion: Full descriptions, illustrations, and results of phylogenetic analyses of the four species along with discussions on related species are provided.