Fires occur in most terrestrial ecosystems where they drive changes in the traits, composition, and diversity of fungal communities. Fires range from rare, stand-replacing wildfires to frequent, prescribed fires used to mimic natural fire regimes. Fire regime factors, including burn severity, fire intensity, and timing, vary widely and likely determine how fungi respond to fires. Despite the importance of fungi to post-fire plant communities and ecosystem functioning, attempts to identify common fungal responses and their major drivers are lacking. This synthesis addresses this knowledge gap and ranges from fire adaptations of specific fungi to succession and assembly fungal communities as they respond to spatially heterogenous burning within the landscape. Fires impact fungi directly and indirectly through their effects on fungal survival, substrate and habitat modifications, changes in environmental conditions, and/or physiological responses of the hosts with which fungi interact. Some specific pyrophilous, or “fire-loving,” fungi often appear after fire. Our synthesis explores whether such taxa can be considered cosmopolitan, and whether they are truly fire-adapted or simply opportunists adapted to rapidly occupy substrates and habitats made available by fires. We also discuss the possible inoculum sources of post-fire fungi and explore existing conceptual models and ecological frameworks that may be useful in generalizing fungal fire responses. We conclude with identifying research gaps and areas that may best transform the current knowledge and understanding of fungal responses to fire.

European, North American and northeastern Asian collections of Xeromphalina section Xeromphalina were studied by sequencing the nuc rDNA ITS1-5.8SITS2 and 28S 5′ regions and partial RNA polymerase II second largest subunit gene (RPB2). Previously designated Xeromphalina campanella I is designated X. campanella s. str. and a neotype for this species from the topotype region is established. This species is shown to be a discrete, cold-tolerant organism that is distributed across North America and Eurasia and does not exhibit significant geographical partitioning. A second closely related phylogenetic species previously designated X. campanella II, proposed as X. enigmatica, cannot be distinguished from X. campanella morphologically but is reproductively isolated and is sympatric with X. campanella across much of Eurasia and North America. Unlike X. campanella it shows geographical partitioning and some of the geographical populations likely have become reproductively isolated. Phylogenetic and geographical evidence suggests that X. enigmatica may have given rise to the eastern North American endemic, Xeromphalina kauffmanii, which also is reproductively isolated and is characterized by a hardwood substrate and a difference in basidiospore shape. Two putatively interbreeding haplotypes are evident for both eastern North American X. kauffmanii and eastern North American X. enigmatica and might be contributions from different glacial refugia. Cryptic taxa related to X. enigmatica are identified but not named due to small sample sizes including Asian taxa 1–5 and an apparent endemic from Idaho and British Columbia. Several species-delineation procedures were attempted and compared with this complex molecular dataset. Rosenberg’s P_AB statistic and P_ID (liberal) were the most liberal, assigning species status to haplotypes or interbreeding clades within species. P_ID (strict) and P_RD (randomly distinct) were more stringent. Ability to intercross was the most stringent criterion for species delineation and did not correlate well with P_AB, P_ID and P_RD delineations.

There is usually little doubt over what is meant by an individual mite, redwood tree, or bacterium, even when considering clonal reproduction, but fungal indivi

Following a late fall wildfire in 2016 in the Great Smoky Mountains National Park, pyrophilous fungi in burn zones were documented over a 2-y period with respect to burn severity and phenology. Nuc rDNA internal transcribed spacer (ITS1-5.8S-ITS2 = ITS) barcodes were obtained to confirm morphological evaluations. Forty-one taxa of Ascomycota and Basidiomycota were identified from burn sites and categorized as fruiting only in response to fire or fruiting enhanced by fire. Twenty-two species of Pezizales (Ascomycota) were among the earliest to form ascomata in severe burn zones, only one of which had previously been documented in the Great Smoky Mountains National Park. Nineteen species of Basidiomycota, primarily Agaricales, were also documented. Among these, only five species (Coprinellus angulatus, Gymnopilus decipiens, Lyophyllum anthracophilum, Pholiota carbonicola, and Psathyrella pennata) were considered to be obligate pyrophilous taxa, but fruiting of two additional taxa (Hygrocybe conica and Mycena galericulata) was clearly enhanced by fire. Laccaria trichodermophora was an early colonizer of severe burn sites and persisted through the winter of 2017 and into spring and summer of 2018, often appearing in close association with Pinus pungens seedlings. Fruiting of pyrophilous fungi peaked 4–6 mo post fire then diminished, but some continued to fruit up to 2.5 y after the fire. In all, a total of 27 previously unrecorded taxa were added to the All Taxa Biodiversity Inventory (ATBI) database (~0.9%). Most pyrophilous fungi identified in this study are either cosmopolitan or have a Northern Hemisphere distribution, but cryptic endemic lineages were detected in Anthracobia and Sphaerosporella. One new combination, Hygrocybe spadicea var. spadicea f. odora, is proposed.

Internally transcribed spacer (ITS) regions of ribosomal DNA are widely used in reconstructing phylogenies at lower taxonomic levels (see, e.g., Vilgalys and Sun 1994 ; Baldwin et al. 1995 ). Ribosomal genes are tandemly repeated, and the paralogs are usually identical due to a poorly understood process of concerted evolution. Proposed mechanisms of concerted evolution include unequal crossing over (Schlotterer and Tautz 1994 ) and biased gene conversion (Hillis et al. 1991 ; Linares, Bowen, and Dover 1994 ). Within-individual diversity for the ribosomal ITS region has been observed and has in some cases been attributed to hybridization (Sang, Crawford, and Stuessy 1995 ; Hugall, Stanton, and Moritz 1999 ).