Abstract
ABSTRACTRussula albonigra is considered a well-known species, morphologically delimited by the context of the basidiomata blackening without intermediate reddening, and the menthol-cooling taste of the lamellae. It is supposed to have a broad ecological range and a large distribution area. A thorough molecular analysis based on four nuclear markers (ITS, LSU, RPB2 and TEF1-α) shows this traditional concept of R. albonigra s. lat. represents a species complex consisting of at least five European, three North American, and one Chinese species. Morphological study shows traditional characters used to delimit R. albonigra are not always reliable. Therefore, a new delimitation of the R. albonigra complex is proposed and a key to the described European species of R. subgen. Compactae is presented. A lectotype and an epitype are designated for R. albonigra and three new European species are described: R. ambusta, R. nigrifacta, and R. ustulata. Different thresholds of UNITE species hypotheses were tested against the taxonomic data. The distance threshold of 0.5% gives a perfect match to the phylogenetically defined species within the R. albonigra complex. Publicly available sequence data can contribute to species delimitation and increase our knowledge on ecology and distribution, but the pitfalls are short and low quality sequences.
Highlights
Molecular identification of species gained importance over the last decades (Matute and Sepulveda 2019)
The two sequences outside the R. albonigra complex are placed in either the R. atramentosa clade or the R. anthracina clade
Our study demonstrated that all species within the R. albonigra complex, supported by the strict genealogic concordance and coalescent-based species delimitation, are strictly distinguished at the threshold of 99.5%, that corresponds to a distance of 0.5% when performing a UNITE search
Summary
Molecular identification of species gained importance over the last decades (Matute and Sepulveda 2019). The main problems with molecular identification are poor taxon coverage and misidentifications in many public sequence databases, as well as high infraspecific variability of DNA regions causing poor performance of the barcoding. Recent studies on lineages of closely related Russula members revealed that they often comprise closely related species diversified by ecological adaptation and isolation by distance or disjunction (Adamčík et al 2016b; Caboň et al 2019; Looney et al 2020). This makes the recognising of these species relevant, despite their similarity in the ITS barcode. Samples identified as R. albonigra in the BOLD database (https://www.boldsystems.org/) do not match any of the species hypothesis under this species name published in UNITE (https://unite.ut.ee/), and vice versa
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