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.

Xylodon (Hymenochaetales, Basidiomycota) is the largest segregate genus of Hyphodontia s.l. Based on molecular and morphological data, 77 species are accepted in Xylodon to date. Phylogenetic analyses of ITS and 28S sequences, including 38 new ITS and 20 28S sequences of Xylodon species, revealed four species new to science. The new taxa X.exilis, X.filicinus, X.follis and X.pseudolanatus from Taiwan, Nepal, Réunion, Belize, and USA are described and illustrated. In addition, species concepts for Odontiavesiculosa from New Zealand and Xylodonlanatus from U.S.A. are revised and the new name X.vesiculosus is proposed. Phylogenetic analyses of the ITS region placed X.spathulatus, X.bubalinus and X.chinensis in a strongly supported clade and demonstrated that they are conspecific. Palifer and Odontiopsis are synonymised under Xylodon based on morphological and sequence data. The following new combinations are proposed: X.erikssonii, X.gamundiae, X.hjortstamii, X.hyphodontinus, X.septocystidiatus and X.verecundus. Line drawings of X.cystidiatus, X.hyphodontinus, X.lanatus and X.vesiculosus, as well as photographs of X.raduloides basidiomata, are provided. A key to X.lanatus and similar species is presented.

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BackgroudHyphoderma setigerum (Fr.) Donk is a white-rot wood-decaying corticoid fungal species. It occurs worldwide from tropical to temperate regions. However, taxonomic studies in recent decades showed that H. setigerum is a species complex with four separate species, before this study.ResultsHyphoderma pinicola sp. nov. was collected on dead wood of Pinus yunnanensis Franch. in the temperate montane belt at 2200–2400 m altitudes, in Yunnan Province of China. Within the H. setigerum complex this new taxon is distinguished by having 2-sterigmate basidia, long basidiospores, and nearly naked septocystidia. A description and illustrations of this new species are provided, along with a key to five species of the H. setigerum complex. Phylogenetic reconstruction based on 5.8S-ITS2 sequences indicated that H. pinicola belongs to the H. setigerum complex and has a separate position within the clade including H. subsetigerum and H. setigerum s.s. Bayesian inference of phylogeny based on two datasets, ITS and 28S nuclear ribosomal DNA sequences, confirmed the independent status of H. pinicola.ConclusionMorphological and phylogenetic studies showed that H. pinicola represents a fifth species of H. setigerum complex.Electronic supplementary materialThe online version of this article (doi:10.1186/s40529-014-0071-5) contains supplementary material, which is available to authorized users.