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 11^th 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.

The class Myxomycetes consists of free-living protists characterised by their complex life cycle, which includes both microscopic (amoebae, flagellates and cists) and macroscopic stages (spore-bearing fruiting bodies, sclerotia, andplasmodia). Withinit, theorder Physarales, with more than 450 recognised species, constitutes the largest group. Although previous studies have shown the polyphyly of some of the traditionally accepted genera, its internal phylogenetic relationships have remained uncertain so far, and together with the lack of data for some keyspecies, itprevented any taxonomic and nomenclatural revisions. We have compiled a substantially expanded data setinterms of both taxon sampling and molecular data, including most of the genera described to date and four unlinked DNA regions, for which we provide partial sequences: nSSU, EF-1α , α-Tub, and mtSSU, analysed through maximum likelihood and Bayesian methods. Our results confirm that the family Didymiaceae is paraphyletic to the rest of Physarales. Within Didymiaceae s. lat., the recent reinstatement of the genus Polyschismium for most species traditionally ascribed to Lepidoderma, except for the type (Ronikieretal.2022), is further supported here, as well as the definite inclusion of the genus Mucilago in Didymium and Lepidoderma s. str.(L. tigrinum) in Diderma (Prikhodkoetal.2023). Additionally, thegenus Diachea is redefined to include some species previously treated in Physaraceae (Craterium spp. with true columella). Within the monophyletic family Physaraceae, most genera are recovered as polyphyletic, suggesting that they should be no longer accepted as currently defined. However, the lack of resolution of some relationships within Physaraceae prevents us from resuscitating or creating several new genera to mitigate polyphyly. Among the well-defined groups with clear molecular signatures, we propose two taxonomic and nomenclatural changes at generic level:1) a new genus, Nannengaella, is proposed for a major clade containing Physarum globuliferum and other species with heavily calcified sporophores and, often, a true calcareous columella;2) Lignydium is resurrected for the clade containing Fuligo muscorum. Additionally, Trichamphora is suggested as the correct name for the clade containing Physarum pezizoideum. The taxonomy and nomenclature of some provisional genera, currently synonymous with Fuligo and Physarum, are disentangled, and we provide a comprehensive and updated nomenclatural conspectus that can be used when better resolved phylogenies are obtained. In total, 22 new combinations are proposed in different genera. Aprovisional key to the genera of the order is also provided.

A new species of the genus Diachea (order Physarales, Myxomycetes, Amoebozoa) is described from Peru. Relevant details on spore germination, as well as morphological and phylogenetic data, are provided. At first glance, the new species shares some morphological similarities with both D. leucopodia, type of the genus, and D. koazei, but it strikingly differs from all other species of its genus by combining a short dark stalk, with a reticulate columella, and clustered spores. Moreover, it seems to be the only species of Diachea exclusively associated with Polylepis tropical forests at elevations above 3500 m. Apart from a comprehensive morphological study of 31 specimens, we here provide phylogenetic evidence to confirm the inclusion of this species in the genus Diachea. Specifically, our phylogenetic analyses of the nuclear 18S rDNA (18S), mitochondrial 17S rDNA (17S), and elongation factor-1 alpha (EF-1α) genes show that the new species is related to D. leucopodia and D. bulbillosa. The remarkably different morphological characters distinguishing the new Diachea from all other species of its genus, along with its particular ecological preferences and geographic distribution, indicate that it is a distinct entity deserving recognition as an independent species.

A new species of Didymium (Myxomycetes), D. xerophilum, is described, and some details of its life cycle are provided. The new species was collected during studies of arid areas of Argentina and Peru. It can be distinguished by the persistent funnel-shaped invagination of the peridium, the top of which appears as a deep umbilicus in closed sporothecae, and the calcareous hypothallus shared among several sporocarps. This combination of characters, with a circumscissile dehiscence of the sporotheca and a cream stalk packed with rhombic lime crystals, is unknown in other described species. Morphology was examined with scanning electron microscopy and light microscopy, and micrographs of relevant details are included here. Phylogenetic analysis with 18S rDNA sequences of different species of Didymium supports the distinct identity of this new species. Some collections of this myxomycete were made at up to 4600 m, an altitude almost unknown for this group of microorganisms.

Human endemic mycoses are potentially fatal diseases caused by a diverse group of fungi that can alter their morphology in response to an increase in temperature. These thermally dimorphic fungi affect both healthy and immunocompromised hosts, causing a substantial health and economic burden. Despite this, the diagnosis of endemic mycoses is still a formidable challenge for several reasons, including similar symptomatology, limited utility of classical diagnostic methods, inaccessibility to reliable molecular approaches in most endemic areas, and a lack of clinical suspicion out of these regions. This review summarizes essential knowledge on thermally dimorphic fungi and the life-threatening diseases they cause. The principle, advantages and limitations of the methods traditionally used for their diagnosis are also described, along with the application status and future directions for the development of alternative diagnostic strategies, which could help to reduce the disease burden in endemic areas.