Abstract
We describe and illustrate two new species of Boletellus section Boletellus, B. aurocontextus sp. nov. and B. areolatus sp. nov., which are generally assumed to be B. emodensis. In this study, we reconstructed separate molecular phylogenetic trees of section Boletellus using the nucleotide sequences of the internal transcribed spacer (ITS) region of nuclear ribosomal DNA, the largest subunit (RPB1) and the second-largest subunit (RPB2) of nuclear RNA polymerase II gene and mitochondrial cytochrome oxidase subunit 3 (cox3) gene. We also examined the morphologies of B. emodensis sensu lato (s.l.) and other related species for comparison. The molecular phylogenetic tree inferred from the sequences of nuclear DNA (ITS, and combined dataset of RPB1 and RPB2) indicated that three genetically and phylogenetically well-separated lineages were present within B. emodensis s.l. These three lineages were also distinguished on the basis of the molecular phylogenetic tree constructed using the sequences of mitochondrial DNA (cox3), suggesting distinct cytonuclear disequilibria (i.e., evidence of reproductive isolation) among these lineages. Therefore, these three lineages can be treated as independent species: B. aurocontextus, B. areolatus, and B. emodensis. Boletellus aurocontextus and B. areolatus are also distinct from B. emodensis by the macro- and microscopic morphologies. Boletellus aurocontextus is characterized by a pileus with bright yellow to lemon yellow context, which can be observed through a gap in the scales, and basidiospores with relatively large length (mean spore length, 21.4 μm; quotient of spore length and width, 2.51). In contrast, B. areolatus is characterized by a pileus with floccose to appressed thin scaly patches, a stipe with pallid or pale cream color at the upper half, and basidiospores with relatively small length (mean spore length, 16.5 μm; quotient of spore length and width, 1.80).
Highlights
The genus Boletellus was originally described by Murrill in the family Boletaceae [1], and ca. 50 species of this genus have since been described worldwide [2]
Based on the molecular phylogenetic trees inferred from the internal transcribed spacer (ITS) sequences (Fig 1A), three genetically and phylogenetically separated lineages were confirmed within B. emodensis s. l
Based on the molecular phylogenetic tree inferred from nuclear ITS and RPB1-RPB2 sequences, we confirmed that B. emodensis s. l. is polyphyletic and separated into three independent clades that were genetically differentiated (Fig 1A and 1B)
Summary
The genus Boletellus was originally described by Murrill in the family Boletaceae [1], and ca. 50 species of this genus have since been described worldwide [2]. Boletellus is an ectomycorrhizal fungus that forms a mutualistic relationship with host trees [3], some species of this genus are often habitat on tree stumps or rotten wood. It is usually characterized by a yellow hymenophore and olive brown elongate to fusoid basidiospores with longitudinally winged basidiospores [4,5]. Seven sections were introduced in this genus by Singer [5], including those characterized by longitudinally winged spores (sections Boletellus, Chrysenteroidei, Ixocephali, and Dictyopodes), smooth spores (section Mirabilis), spores with imbedded short spines (section Allospori), and reticulate spores (section Retispori). Only a single species B. emodensis (Berk.) Singer, was reported from Japan [12,13]; this species was first described as B. floriformis Imazeki [17], but later synonymized with B. emodensis [9]
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