Revisions to the Gliophorus irrigatus complex (Agaricales, Hygrophoraceae, Gliophorus, section Unguinosae) including four new species, one new combination and comparisons of basidiome vs. eDNA distributions

Here, we report the discovery of four new agaricoid fungi in the <i>Gliophorus irrigatus</i> complex of the family Hygrophoraceae. <i>Gliophorus alboviscidus</i> <b>sp. nov</b>. from the UK is morphologically identical to the European <i>G. irrigatus</i> (which we neotypify), except that its basidiome is white or pale Buff-coloured vs. brownish-grey. Two new species from eastern North America, <i>Gliophorus fumosus</i> <b>sp. nov</b>. (provisional name <i>Gliophorus</i> sp. 'irrigatus-IN01') and <i>Gliophorus parafumosus</i> <b>sp. nov</b>. (previously labelled <i>G. irrigatus</i>) resemble <i>G. irrigatus</i> s.s. in grey colour and morphology, but their distributions are restricted to North America. Phylogenetic reconstruction revealed that the two North American groups form distinct clades, with > 10% ITS sequence divergence from European <i>G. irrigatus</i> s.s. and from each other. Though <i>G. alboviscidus</i> <b>sp. nov</b>. is currently known only from two locations in the UK, searches for related sequences from eDNA (environmental DNA) sequence repositories (UNITE/GlobalFungi) suggested that this species is more widely distributed in Eurasia. <i>G. fumosus</i> and <i>G. parafumosus</i> sequences from eastern North America were divergent from both European <i>G. irrigatus</i> and <i>G. alboviscidus</i>; both were more closely related to another species with a strong odour and white/Buff basidiomes from north-western North America, <i>Hygrophorus subaromaticus</i>, for which we sequenced the holotype and recombine in the genus <i>Gliophorus</i>. We also describe a new species from north-western North America, <i>G. calunus</i> <b>sp. nov</b>. (provisional name <i>Gliophorus</i> sp. 'irrigatus-CA01'), based on vouchered specimens photographed and sequenced by a paraprofessional group, CA FUNDIS. We highlight the importance of citizen-scientist groups and paraprofessionals in documenting macrofungal species and their distributions via databases, such as iNaturalist, Mushroom Observer and MycoMap. Further, we discuss reasons that eDNA distributions are often larger than known distributions of basidiomes, including <i>G. alboviscidus</i> and <i>G. fumosus</i>.