Stop black and white thinking: Russula subgenus Compactae (Russulaceae, Russulales) in Europe revised

Russula subgenus Compactae is a group of ectomycorrhizal basidiomycetes, usually with large pileate fruitbodies. European members of the group are characterised by the absence of bright colours on the surfaces of their pilei, the context turning grey to black after cutting, the abundance of short lamellulae in the hymenophore, and spores with an inamyloid suprahilar spot and with low reticulate ornamentation. Our multi-locus phylogenetic study confirmed that this morphological delimitation corresponds to a well-supported clade. Within this clade, 16 species are recognised in Europe, of which five belong to the R. albonigra lineage and were described in a previous study, while eleven are fully described in this study. The application of the names R. acrifolia, R. adusta, R. anthracina, R. atramentosa, R. densissima, R. nigricans and R. roseonigra is based on the position of sequences retrieved from types or authentic material. Based on type sequences, R. fuliginosa is synonymised with R. anthracina and two varieties of R. anthracina are considered synonyms of R. atramentosa. The application of the name R. densifolia is based on a morphological match with the traditional species interpretation and the neotype specimen. Three species are described as new, R. marxmuelleriana sp. nov., R. picrophylla sp. nov. and R. thuringiaca sp. nov. This study recognises three major lineages and two species with isolated positions within the European Compactae and a morphological barcode was assigned to the species using an analysis of 23 selected characters. A search of publicly available sequences from the UNITE database revealed that the majority of species are host tree generalists and widely distributed in temperate and Mediterranean areas of Europe. Russula adusta is the only species so far proven to form ectomycorrhiza exclusively with conifers. Citation: De Lange R, Kleine J, Hampe F, et al. 2023. Stop black and white thinking: Russula subgenus Compactae (Russulaceae, Russulales) in Europe revised. Persoonia 51: 152-193. doi: 10.3767/persoonia.2023.51.04.

Four new species of Russula subsection Roseinae from tropical montane forests in western Panama

Species of the genus Russula are key components of ectomycorrhizal ecosystems worldwide. Nevertheless, their diversity in the tropics is still poorly known. This study aims to contribute to the knowledge of the diversity of Russula species classified in subsection Roseinae based on specimens recently collected in tropical montane rainforests in western Panama. A five gene multilocus phylogeny based on the nuclear markers ITS nrDNA, MCM7, RPB1, RPB2 and TEF-1α was constructed to identify the systematic position of 22 collections from Panama. Four new species, Russula cornicolor, Russula cynorhodon, Russula oreomunneae and Russula zephyrovelutipes are formally described and illustrated. None of the four species are sister species and they are more closely related to North American or Asian species. Two of the newly described species were associated with the ectomycorrhizal tree species Oreomunnea mexicana, while the other two species were associated with Quercus species. All four species are so far only known from mountains in western Panama.

Enlightening the black and white: species delimitation and UNITE species hypothesis testing in the Russula albonigra species complex

Russula 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.

Morphological and genetic diversification of Russula floriformis, sp. nov., along the Isthmus of Panama

Species of Russula are ubiquitous members of ectomycorrhizal fungal communities in tropical ecosystems. However, an important part of the total tropical diversity of this genus and its biogeographic patterns is unknown due to the lack of studies on Russula in tropical ecosystems. We combined molecular, morphological, ecological, and biogeographic data to elaborate concepts for two new subspecies of R. floriformis (subsection Substriatinae). Russula floriformis subsp. floriformis and R. floriformis subsp. symphoniae are described as new from montane forest dominated by Quercus and/or Oreomunnea (Fagales) from Colombia and Panama, respectively. Phylogenies were constructed using nuc rDNA internal transcribed spacer region ITS1-5.8S-ITS2 (ITS), D1-D2 domains of nuc 28S rDNA (28S), and partial regions of the second largest subunit of RNA polymerase II (rpb2) and translation elongation factor 1-alpha (tef1). Similar environmental conditions, similar morphology, and an ITS sequence similarity higher than 99% with only three different positions indicate that these two subspecies are closely related. Detailed observations of microscopic structures and analyses of further DNA loci, however, revealed morphological and molecular characteristics that allow distinguishing the two subspecies of R. floriformis. Spatial distribution and phylogenetic proximity of the two Russula subspecies and their ectomycorrhizal hosts, i.e., species of Quercus, suggest that their diversification is a result of comigration, adaptation, and geographic isolation along the Isthmus of Panama during the Pliocene and Pleistocene.

Novel diversity in Lactifluus section Gerardii from Asia: five new species with pleurotoid or small agaricoid basidiocarps

The ectomycorrhizal milkcap genus Lactifluus (Russulaceae) is commonly found in tropical and subtropical forests of Southeast Asia. During several sampling expeditions in Thailand, multiple collections of Lactifluus (Lf.) species with pleurotoid or small agaricoid basidiocarps were found. A molecular study was combined with a morphological study, in which the collections were compared with herbarium material. The molecular study indicated that four Thai collections belonged to undescribed species within Lactifluus section Gerardii, as was also the case for herbarium collections of a pleurotoid species from Nepal. One other collection from Thailand appeared closely related to Lf. uyedae, known only from Japan. Five species are described as new in the genus: Lf. auriculiformis, Lf. gerardiellus, Lf. bhandaryi, Lf. pulchrellus, and Lf. raspei.

Molecular inference, multivariate morphometrics and ecological assessment are applied in concert to delimit species in the Russula clavipes complex

Species of Russula subsect. Xerampelinae are notoriously difficult to identify and name and have not been subject to molecular study. A group of species, referred to here as the R. clavipes complex, growing in association with Salix, Betula and Populus as well as coniferous tree species from temperate to arctic and alpine habitats, were examined. Analyses of the nuc rDNA internal transcribed spacer (ITS) region and a numerical analysis of morphological characters were used. The R. clavipes complex is a monophyletic group within Russula subsect. Xerampelinae, according to molecular results. The complex includes three species: R. nuoljae is a phylogenetically and morphologically well-supported species while the other two, R. clavipes and R. pascua, are similar based on ITS data and morphology but separate based on their ecology. Russula pseudoolivascens is conspecific with R. clavipes Several combinations of characters traditionally used in the taxonomy of R. subsect. Xerampelinae are inappropriate for species delimitation in this group and the adequacy of the ITS for species identification in this group is discussed. Detailed microscopic observations on the type collection of R. nuoljae are presented and illustrated, along with a key to the European members of R. subsect. Xerampelinae.

Into and out of the tropics: global diversification patterns in a hyperdiverse clade of ectomycorrhizal fungi

Ectomycorrhizal (ECM) fungi, symbiotic mutualists of many dominant tree and shrub species, exhibit a biogeographic pattern counter to the established latitudinal diversity gradient of most macroflora and fauna. However, an evolutionary basis for this pattern has not been explicitly tested in a diverse lineage. In this study, we reconstructed a mega-phylogeny of a cosmopolitan and hyperdiverse genus of ECM fungi, Russula, sampling from annotated collections and utilizing publically available sequences deposited in GenBank. Metadata from molecular operational taxonomic unit cluster sets were examined to infer the distribution and plant association of the genus. This allowed us to test for differences in patterns of diversification between tropical and extratropical taxa, as well as how their associations with different plant lineages may be a driver of diversification. Results show that Russula is most species-rich at temperate latitudes and ancestral state reconstruction shows that the genus initially diversified in temperate areas. Migration into and out of the tropics characterizes the early evolution of the genus, and these transitions have been frequent since this time. We propose the 'generalized diversification rate' hypothesis to explain the reversed latitudinal diversity gradient pattern in Russula as we detect a higher net diversification rate in extratropical lineages. Patterns of diversification with plant associates support host switching and host expansion as driving diversification, with a higher diversification rate in lineages associated with Pinaceae and frequent transitions to association with angiosperms.