No abstract

Numerous taxa of Hebeloma have been reported in association with Salix, Dryas, and Betula in arctic-alpine habitats. However, species are notoriously difficult to delineate because morphological features overlap, and previously there was little reliable molecular data available. Recent progress in ITS-sequencing within the genus, coupled with an extensive database of parametrically described collections, now allows comparisons between species and their distributions. Here we report 16 species of Hebeloma from the Rocky Mountain alpine zone from some of the lowest latitudes (latitude 36°–45°N) and highest elevations (3000–4000 m) for arctic-alpine fungi in the northern hemisphere. Twelve of these species have been reported from arctic-alpine habitats in Europe and Greenland and are now molecularly confirmed from the Middle and Southern Rockies, greatly expanding their distribution. These are: Hebelomaalpinum, H.aurantioumbrinum, H.dunense, H.hiemale, H.marginatulum, H.mesophaeum, H.nigellum, H.oreophilum, H.subconcolor, H.spetsbergense, H.vaccinum, and H.velutipes. Hebelomahygrophilum is known from subalpine habitats in Europe, but was never recorded in arctic-alpine ecology. Three species recorded from the Rockies, but as yet not reported from Europe, are H.alpinicola, H.avellaneum, and H.excedens. The last two have never previously been reported from an arctic-alpine habitat. For all three of these species, the holotypes have been studied morphologically and molecularly, and have been incorporated into the analysis.

Nomenclatural type definitions are one of the most important concepts in biological nomenclature. Being physical objects that can be re-studied by other researchers, types permanently link taxonomy (an artificial agreement to classify biological diversity) with nomenclature (an artificial agreement to name biological diversity). Two proposals to amend the International Code of Nomenclature for algae, fungi, and plants (ICN), allowing DNA sequences alone (of any region and extent) to serve as types of taxon names for voucherless fungi (mainly putative taxa from environmental DNA sequences), have been submitted to be voted on at the 11th International Mycological Congress (Puerto Rico, July 2018). We consider various genetic processes affecting the distribution of alleles among taxa and find that alleles may not consistently and uniquely represent the species within which they are contained. Should the proposals be accepted, the meaning of nomenclatural types would change in a fundamental way from physical objects as sources of data to the data themselves. Such changes are conducive to irreproducible science, the potential typification on artefactual data, and massive creation of names with low information content, ultimately causing nomenclatural instability and unnecessary work for future researchers that would stall future explorations of fungal diversity. We conclude that the acceptance of DNA sequences alone as types of names of taxa, under the terms used in the current proposals, is unnecessary and would not solve the problem of naming putative taxa known only from DNA sequences in a scientifically defensible way. As an alternative, we highlight the use of formulas for naming putative taxa (candidate taxa) that do not require any modification of the ICN.

Hebeloma subsection Denudata includes the type of H. section Denudata, Hebeloma crustuliniforme, as well as the majority of the taxa commonly included in the Hebeloma crustuliniforme complex. Complementing the work of D.K. Aanen and co-workers, and using refined morphological and molecular methods we were able to recognize further individual taxa within the section. Fifteen species occurring in Europe are assigned to H. subsect. Denudata. Of these, we describe eight species as new, namely H. aanenii, H. aurantioumbrinum, H. geminatum, H. louiseae, H. luteicystidiatum, H. pallidolabiatum, H. perexiguum and H. salicicola. Naucoria bellotiana, a species very similar to H. alpinum is recombined into Hebeloma. A key to Hebeloma subsect. Denudata is provided. We demonstrate that within this subsection there is good overall consistency between morphological, phylogenetic and biological species concepts. In contrast to current opinion, in this group there is little species overlap, particularly when also considering species frequencies, between arctic and alpine floras on one hand and temperate on the other.

Hebeloma velutipes is one of the most common and abundant members of the ectomycorrhizal basidiomycete genus and H. sinapizans is one of its oldest and most commonly recorded species. Using large sample sizes, several loci and the analysis of types, we explored the taxonomy, species limits, distribution and the infrageneric classification of these two species and their relatives. By relying almost exclusively on sequenced material, we were able to attain a marked refinement of species descriptions. Phylogenetic results are congruent with respect to the delimitation of species, but suggest conflicting evolutionary histories of the species phylogeny. Using multi-species coalescent analysis, phylogenetic support for H. sects. Velutipes and Sinapizantia was assessed, finding clear support for H. sect. Sinapizantia but ambiguous results for H. sect. Velutipes. One species, H. subconcolor, previously accommodated in H. sect. Denudata, is placed in H. sect. Velutipes. Hebeloma bulbiferum, so far not considered in systematic treatments, is shown to belong to H. sect. Sinapizantia. Unexpectedly, H. velutipes turned out to be distinct from H. leucosarx. Hebeloma erebium comb. nov., H. celatum sp. nov. and H. quercetorum, formerly treated as a single species (H. quercetorum), are demonstrated to be three taxa that are clearly distinct in molecular terms, even though, morphologically, they can be deceptively similar; H. erebium and H. quercetorum are, moreover, geographically distinct. The morphological characters used to distinguish the ten recognised European species are outlined. Finally, a lectotype and an epitype are designated for H. sinapizans and a lectotype for H. quercetorum