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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.

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It is widely recognised that there is no consistent use of the name H. crustuliniforme. The name has been used to represent a number of different taxa and indeed taxa from sections of Hebeloma that are morphologically and molecularly well separated. The holotype of H. crustuliniforme is plate 308 Bulliard from 1787 and while it can be interpreted, no such interpretation can be without ambiguity. It is clear from existing literature that modern authors have applied numerous different interpretations to this name and no real consensus exists. Indeed it appears that at various times most of the medium to large species within both sections Denudata and Velutipes Vesterh. have been referred to as H. crustuliniforme. Within this paper an epitype is selected for H. crustuliniforme in order to give the taxon a precise meaning and a detailed species description is given. Molecular data combined with the results of intercompatibility tests of Aanen and Kuyper published earlier support the definition of H. crustuliniforme adopted in this paper as a distinct taxon and as a biological species. We strongly recommend that this taxon be referred to as Hebeloma crustuliniforme (Bull.) Qu,l. emend. Vesterh., U. Eberh. & Beker in order to emphasise that it is the specific taxon rather than the complex to which it is being referred

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