Pacific boletes: Implications for biogeographic relationships

Broadening the Knowledge of Mexican Boletes: Addition of a New Genus, Seven New Species, and Three New Combinations

Boletes are one of the most common groups of fungi in temperate, subtropical, and tropical ecosystems. In Mexico, the northern region has mainly been explored in terms of bolete diversity. This study describes a new genus and seven new species based on macromorphological, micromorphological, molecular, phylogenetic, and ecological data. Garcileccinum gen. nov. is typified with G. salmonicolor based on multigene phylogenetic analysis of nrLSU, RPB2, and TEF1, and it is closely related to Leccinum and Leccinellum. Garcileccinum viscosum and G. violaceotinctum are new combinations. Boletellus minimatenebris (ITS, nrLSU, and RPB2), Cacaoporus mexicanus (RPB2 and ATP6), Leccinum oaxacanum, Leccinum juarenzense (nrLSU, RPB2, and TEF1), Tylopilus pseudoleucomycelinus (nrLSU and RPB2), and Xerocomus hygrophanus (ITS, nrLSU, and RPB2) are described as new species. Boletus neoregius is reclassified as Pulchroboletus neoregius comb. nov. based on morphological and multigene phylogenetic analysis (ITS and nrLSU), and its geographic distribution is extended to Central Mexico, since the species was only known from Costa Rica. Furthermore, T. leucomycelinus is a new record from Mexico. This study contributes to increasing our knowledge of boletes and expands the diversity found in Mexican forests.

Kgaria (Boletaceae, Boletoideae) gen. nov. in Australia: Neither a Tylopilus nor a Porphyrellus

Kgaria is described as a new porphyrellus-like genus of Boletaceae to accommodate Tylopilus cyanogranulifer, a dark brown to dull lilac/violet, or rarely, nearly black bolete with a series of oxidation reactions progressing from blue to red then nearly black and a dark brown spore deposit. Idiosyncratic blue-green pigment encrustations (cyanogranules) and a similarly colored reaction of the hyphae located on pileus and stipe surfaces are also diagnostic. Phylogenetic analyses of nuclear large-subunit rDNA (nrLSU), translation elongation factor 1-alpha (tef-1), and the second largest subunit of RNA polymerase II (rpb2) infer Kgaria as a unique generic lineage with two species, one of which is newly described (K. similis). Tylopilus olivaceoporus, originally described at the same time and as distinct from T. cyanogranulifer, appears to be conspecific with the latter. Some darkly pigmented taxa with similar oxidation reactions that were recently described from Brazil, Guyana, and China are further supported by morphology and molecular data as discrete lineages in separate genera in subfamily Boletoideae. Citation: Halling RE, Fechner NA, Holmes G, Davoodian N (2023). Kgaria (Boletaceae, Boletoideae) gen. nov. in Australia: Neither a Tylopilus nor a Porphyrellus. Fungal Systematics and Evolution 12: 31-45. doi: 10.3114/fuse.2023.12.02.

Ectomycorrhizal Assemblages of Invasive Quercus rubra L. and Non-Invasive Carya Nutt. Trees under Common Garden Conditions in Europe

Invasive tree species change biodiversity, nutrient cycles, and ecosystem services, and can turn native ecosystems into novel ecosystems determined by invaders. In the acclimatization and invasion of alien tree species, the crucial role is played by ectomycorrhizal (ECM) fungi. We tested ECM fungi associated with Quercus rubra and Carya trees that are alien to Europe. Quercus rubra is among the most invasive tree species in Europe, and the Carya species are not considered invasive. Both form ectomycorrhizal symbiosis, and in their native range in North America, coexist in oak-hickory forests. Six study stands were located in Kórnik Arboretum: three for Q. rubra and three for Carya trees. Ectomycorrhizal fungi were assessed by molecular identification of ECM roots. We identified 73 ECM fungal taxa of 23 ECM phylogenetic lineages. All identified ECM fungi were native to Europe. Similar richness but different composition of ECM taxa were found on Q. rubra and Carya roots. Phylogenetic lineages /tomentella-thelephora, /russula-lactarius, and /genea-humaria were most abundant on both Carya and Q. rubra roots. Lineages /tuber-helvella and /entoloma were abundant only on Carya, and lineages /pisolithus-scleroderma and /cortinarius were abundant only on Q. rubra roots. Analysis of similarities revealed a significant difference in ectomycorrhizal assemblages between invasive Q. rubra and non-invasive Carya. Highlights: (1) under common garden conditions, ECM taxa richness was similar on Q. rubra and Carya roots; (2) ECM taxa composition differed between invasive Q. rubra and non-invasive Carya; (3) high abundance of long-distance exploration type (lineages from Boletales) was on Q. rubra; and (4) high abundance of short-distance exploration type (e.g., /tuber-helvella) was on Carya.

Phylogenetic analysis reveals the new genus Amoenoboletus from Asia and New Zealand

The Asia-Pacific region is renowned to harbor nearly half of the global hot spots of biodiversity. Accordingly, many endemic species of boletes have already been recorded from this geographic region. However, the majority of the specific descriptions of reported boletoid species follow classical concepts of taxonomy, and by comparison only a few taxa have been corroborated by modern molecular techniques. In this study, we focused on specimens in a new clade uncovered by our previous studies. By careful reexamination of macroscopic and microscopic characters of Boletus granulopunctatus, originally described from Japan, and Xerocomus mcrobbii, originally described from New Zealand, we discovered a new genus and species Amoenoboletus miraculosus from Sabah, Malaysia. In addition, three new combinations in Amoenoboletus are proposed, and a dichotomous key to species in the genus is provided. The phylogenetically close relationship among Amoenoboletus species suggests a tight geographic correlation in the Asia-Pacific region.

Three new species of Smithiomyces from tropical Asia support an amphi-Pacific disjunct distribution in the genus

Smithiomyces is reported for the first time from tropical regions in China, thus expanding its known native geographic range from the Neotropics to tropical Asia. Phylogenetic evidence from four nuclear loci supports the monophyly of Smithiomyces and a close evolutionary relationship with the nonmonophyletic genera Melanophyllum and Cystolepiota in the Agaricaceae. Detailed morphological descriptions are provided for three newly described species from China: S. asiaticus, S. heterosporus, and S. lepiotoides. Illustrations of fresh basidiomata in the field, line drawings of key anatomical features, microscopic images of anatomical features, scanning electron microscope (SEM) images of basidiospores, and a key to known species of Smithiomyces are also provided.

Behind the veil - exploring the diversity in Phallus indusiatus s.l. (Phallomycetidae, Basidiomycota)

Studies have demonstrated that many cosmopolitan species actually consist of divergent clades that present high levels of morphological stasis throughout their evolutionary histories. Phallusindusiatus s.l. has been described as a circum-tropical species. However, this distribution may actually reflect the lack of taxonomic resolution due to the small number of diagnostic morphological characters, which leads to the identification of new records as populations of P.indusiatus. Here, we examine the diversity of P.indusiatus-like species in Brazilian Amazonia. We show a clear congruence between detailed morphological data and ITS, nuc-LSU and atp6 based phylogenetic analyses and three new species are described within the Brazilian indusiate clade. These results highlight the importance of more detailed investigation, with the inclusion of molecular information, in Neotropical fungi.

Neoboletusantillanus sp. nov. (Boletaceae), first report of a red-pored bolete from the Dominican Republic and insights on the genus Neoboletus

Neoboletusantillanus sp. nov. appears to be the only red-pored bolete known from the Dominican Republic to date. It is reported as a novel species to science based on collections gathered in a neotropical lowland mixed broadleaved woodland. A detailed morphological description, color images of fresh basidiomes in habitat and line drawings of the main anatomical features are provided and relationships with phylogenetically and phenotypically similar taxa are discussed. Three genomic regions (nrITS, nrLSU/28S and rpb2) have been sequenced in order to reinforce the recognition of the new species and to elucidate its taxonomic affiliation within Neoboletus.

Phylogeny, biogeography and taxonomic re-assessment of Multifurca (Russulaceae, Russulales) using three-locus data

Multifurca is a small genus newly established to accommodate lactarioid and russuloid species with some characters reminiscent of corticoid members of Russulaceae. It shows an amphi-pacific distribution with strong preference for the tropical zone of the Northern Hemisphere and thus has particular significance for biogeographical study. Using worldwide samples and three loci (ITS, 28S rDNA and rpb2), we demonstrated that Multifurca is split into two highly supported major clades that are here recognized at the subgeneric level: subg. Furcata subg. nov. exclusively includes lactarioid species, while subg. Multifurca includes species with a russuloid habit. Using phylogenetic species recognition and comparison of genetic distances we recognize five new and six previously described species, almost double the known number of species before this study. Molecular dating using a Bayesian method suggested that Multifurca originated in early Paleocene and diversified in the Eocene. The most recent interspecific divergences occurred both in Asia and America, roughly at the same time around the Pliocene. Ancestral area reconstruction and comparisons of genetic distances and morphology suggested an early divergence within Australasia or tropical Asia. From the early Miocene to Pliocene, multiple dispersals/migrations to Australasia and North America by island hopping or land bridge likely happened. Vicariance at the late Tertiary might be the most likely mechanism accounting for the eastern Asia-southeastern North America and Australasia-tropical Asia disjunct distributions. The shared polymorphisms in the ITS alignment, numerous degenerated base pairs in the rpb2 sequences and weak conflict between the ITS and LSU genealogies of M. subg. Furcata suggest recent speciation. Host specificity of Multifurca species or species pairs is relatively low. Host shifts are believed to have aided establishment in new territories during the dispersals and migrations.

Two new species and one new record of the genus Tylopilus (Boletaceae) from Indian Himalaya with morphological details and phylogenetic estimations

Tylopilus himalayanus and T. pseudoballoui are described as new species from two Himalayan states (Sikkim and Uttarakhand) in India. Tylopilus himalayanus is characterised by a unique combination of features: reddish- or brownish-grey to purplish-grey then brown to reddish-brown or darker pileus, absence of olive or violet tinges on stipe surface, angular pores, stipe without reticulum or rarely with a faint reticulum restricted to the very apex, bitter taste of the context and positive macrochemical colour reaction of the stipe context with KOH (dark orange) and FeSO₄ (dark green), medium sized (10.9-14.4 × 3.9-4.9 µm) basidiospores and occurrence under coniferous trees; T. pseudoballoui is distinguished by orange-yellow to brown-yellow sticky pileus, pale yellow pore surface with pinkish hues that turns pale to greyish-orange on bruising; angular pores, stipe concolorous to pileus with pruinose but never reticulate surface, ixocutis pattern of pileipellis and occurrence under broadleaf trees. Another species, T. neofelleus, which was reported earlier from China and Japan, was also collected from Sikkim and reported for the first time from India. All three species are described with morphological details and two-locus based (nrLSU and nrITS) phylogenetic data.

Speciation in progress? A phylogeographic study among populations of Hemitrichia serpula (Myxomycetes)

Myxomycetes (plasmodial slime molds, Amoebozoa) are often perceived as widely distributed, confounding to the “everything is everywhere” hypothesis. To test if gene flow within these spore-dispersed protists is restricted by geographical barriers, we chose the widespread but morphologically unmistakable species Hemitrichia serpula for a phylogeographic study. Partial sequences from nuclear ribosomal RNA genes (SSU) revealed 40 ribotypes among 135 specimens, belonging to three major clades. Each clade is dominated by specimens from a certain region and by one of two morphological varieties which can be differentiated by SEM micrographs. Partial sequences of the protein elongation factor 1 alpha (EF1A) showed each clade to possess a unique combination of SSU and EF1A genotypes. This pattern is best explained assuming the existence of several putative biospecies dominating in a particular geographical region. However, occasional mismatches between molecular data and morphological characters, but as well heterogeneous SSU and heterozygous EF1A sequences, point to ongoing speciation. Environmental niche models suggest that the putative biospecies are rather restricted by geographical barriers than by macroecological conditions. Like other protists, myxomycetes seem to follow the moderate endemicity hypothesis and are in active speciation, which is most likely shaped by limited gene flow and reproductive isolation.

Divergence Times and Phylogenetic Patterns of Sebacinales, a Highly Diverse and Widespread Fungal Lineage

Patterns of geographic distribution and composition of fungal communities are still poorly understood. Widespread occurrence in terrestrial ecosystems and the unique richness of interactions of Sebacinales with plants make them a target group to study evolutionary events in the light of nutritional lifestyle. We inferred diversity patterns, phylogenetic structures and divergence times of Sebacinales with respect to their nutritional lifestyles by integrating data from fossil-calibrated phylogenetic analyses. Relaxed molecular clock analyses indicated that Sebacinales originated late Permian within Basidiomycota, and their split into Sebacinaceae and Serendipitaceae nom. prov. likely occurred during the late Jurassic and the early Cretaceous, coinciding with major diversifications of land plants. In Sebacinaceae, diversification of species with ectomycorrhizal lifestyle presumably started during the Paleocene. Lineage radiations of the core group of ericoid and cavendishioid mycorrhizal Sebacinales started probably in the Eocene, coinciding with diversification events of their hosts. The diversification of Sebacinales with jungermannioid interactions started during the Oligocene, and occurred much later than the diversification of their hosts. Sebacinales communities associated either with ectomycorrhizal plants, achlorophyllous orchids, ericoid and cavendishioid Ericaceae or liverworts were phylogenetically clustered and globally distributed. Major Sebacinales lineage diversifications started after the continents had drifted apart. We also briefly discuss dispersal patterns of extant Sebacinales.

Long-distance dispersal and speciation of Australasian and American species of Cortinarius sect. Cortinarius

We present a multigene phylogeny (partial nuc rDNA and RPB2) of Cortinarius sect. Cortinarius (i.e. the C. violaceus group), which reveals eight species distributed in Europe, Australasia, South America, Central America and North America. Relaxed molecular clock analyses suggested that diversification began during the Miocene, thus rejecting more ancient Gondwanan origin scenarios among the taxa currently occurring in the northern and southern hemispheres. There was strong support for an Australasian origin of the C. violaceus group with initial dispersal to the Neotropics, followed by migration into North America and Europe. A dispersal-extinction cladogenesis model that includes a parameter for founder effects was the most highly supported biogeographic model in the program BioGeoBEARS. A maximum likelihood analysis showed the most recent common ancestor of sect. Cortinarius was an angiosperm ectomycorrhizal associate. Ancestral associations at the plant family level, however, were ambiguous. Of eight recovered species-level lineages, C. violaceus is the only one that associates with Pinaceae and the only species to associate with both Pinaceae and angiosperms. This analysis showed that long-distance dispersal and founder event speciation have been important factors during evolution of the C. violaceus group.

Molecular phylogeny and taxonomy of the genus Veloporphyrellus

Veloporphyrellus is a genus known from North and Central America, southeastern Asia, and Africa. Because species of this genus are phenotypically similar to some taxa in several genera, such as Boletellus, Leccinum, Strobilomyces, Suillus and Tylopilus s.l. belonging to Boletales, its phylogenetic disposition has never been addressed. We analyzed four DNA regions, the nuclear ribosomal LSU and tef-1α, and the mitochondrial mtSSU and atp6 genes, to investigate the phylogenetic disposition of Veloporphyrellus. Although the monophyly of the genus and its systematic placement within the Boletaceae was well supported, its relationship to other genera was not resolved. Morphologically Veloporphyrellus is distinguished from other boletoid genera by the combination of the pinkish or grayish pink hymenophore, the membranous veil hanging on the pilea margin, the trichoderm-like pileus covering and the smooth basidiospores. Five species, including two new species and two new combinations, are described and illustrated. A key to the species of Veloporphyrellus also is provided.

Phylogenetic overview of the Boletineae

The generic and sub-generic relationships in the Boletineae (Boletales) were studied using nuclear large subunit (nuc-lsu), translation elongation factor 1-alpha (tef1), and DNA directed RNA polymerase largest subunit (RPB1). The Boletineae, with the exclusion of Hydnomerulius pinastri, was strongly supported and the status of the families Boletaceae and Paxillaceae is discussed. Members of the genus Boletus are found throughout the phylogeny, with the majority not closely related to the type species, Boletus edulis. Many of the traditional, morphologically defined genera are not supported as monophyletic and additional sampling and taxonomic revisions are needed. The majority of the Boletineae are confirmed or putatively ectomycorrhizal (ECM), but two putatively mycoparasitic lineages (one lineage of Buchwaldoboletus lignicola and Chalciporus piperatus and the second Pseudoboletus parasiticus) are strongly supported.

Intraspecific variation of the aquatic fungus Articulospora tetracladia: an ubiquitous perspective

The worldwide-distributed aquatic fungus Articulospora tetracladia Ingold is a dominant sporulating species in streams of the Northwest Iberian Peninsula. To elucidate the genetic diversity of A. tetracladia, we analyzed isolates collected from various types of plant litter or foam in streams from North and Central Portugal and North Spain, between 2000 and 2010. Genetic diversity of these fungal populations was assessed by denaturing gradient gel electrophoresis (DGGE) fingerprints and by using ITS1-5.8S-ITS2 barcodes. Moreover, ITS1-5.8S-ITS2 barcodes of A. tetracladia reported in other parts of the world (Central Europe, United Kingdom, Canada, Japan and Malaysia) were retrieved from the National Center for Biotechnology (NCBI) and the National Institute of Technology and Evaluation Biological Resource Center (NBRC) to probe into genetic diversity of A. tetracladia. PCR-DGGE of ITS2 region of 50 Iberian fungal isolates distinguished eight operational taxonomic units (OTUs), which were similar to those obtained from neighboring trees based on ITS2 gene sequences. On the other hand, ITS1-5.8S-ITS2 barcodes of 68 fungal isolates yielded nine OTUs, but five fungal isolates were not assigned to any of these OTUs. Molecular diversity was highest for OTU-8, which included only European isolates. Two haplotypes were observed within OTU-8 and OTU-9, while only one haplotype was found within each of the remaining OTUs. Malaysia did not share haplotypes with other countries. Overall results indicate that, apart from the Malaysian genotypes, A. tetracladia genotypes were geographically widespread irrespective of sampling time, sites or substrates. Furthermore, PCR-DGGE appeared to be a rapid tool for assessing intraspecific diversity of aquatic hyphomycetes.

Intercontinental divergence in the Populus-associated ectomycorrhizal fungus, Tricholoma populinum

The ectomycorrhizal fungus Tricholoma populinum is host-specific with Populus species. T. populinum has wind-dispersed progagules and may be capable of long-distance dispersal. In this study, we tested the hypothesis of a panmictic population between Scandinavia and North America. DNA sequences from five nuclear loci were used to assess phylogeographic structure and nucleotide divergence between continents. Tricholoma populinum was composed of Scandinavian and North American lineages with complete absence of shared haplotypes and only one shared nucleotide mutation. Divergence of these lineages was estimated at approx. 1.7-1.0 million yr ago (Ma), which occurred after the estimated divergence of host species Populus tremula and Populus balsamifera/Populus trichocarpa at 5 Ma. Phylogeographic structure was not observed within Scandinavian or North American lineages of T. populinum. Intercontinental divergence appears to have resulted from either allopatric isolation; a recent, rare long-distance dispersal founding event followed by genetic drift; or the response in an obligate mycorrhizal fungus with a narrow host range to contractions and expansion of host distribution during glacial and interglacial episodes within continents. Understanding present genetic variation in populations is important for predicting how obligate symbiotic fungi will adapt to present and future changing climatic conditions.

Extensive gene flow over Europe and possible speciation over Eurasia in the ectomycorrhizal basidiomycete Laccaria amethystina complex

Biogeographical patterns and large-scale genetic structure have been little studied in ectomycorrhizal (EM) fungi, despite the ecological and economic importance of EM symbioses. We coupled population genetics and phylogenetic approaches to understand spatial structure in fungal populations on a continental scale. Using nine microsatellite markers, we characterized gene flow among 16 populations of the widespread EM basidiomycete Laccaria amethystina over Europe (i.e. over 2900 km). We also widened our scope to two additional populations from Japan (10(4) km away) and compared them with European populations through microsatellite markers and multilocus phylogenies, using three nuclear genes (NAR, G6PD and ribosomal DNA) and two mitochondrial ribosomal genes. European L. amethystina populations displayed limited differentiation (average F(ST) = 0.041) and very weak isolation by distance (IBD). This panmictic European pattern may result from effective aerial dispersal of spores, high genetic diversity in populations and mutualistic interactions with multiple hosts that all facilitate migration. The multilocus phylogeny based on nuclear genes confirmed that Japanese and European specimens were closely related but clustered on a geographical basis. By using microsatellite markers, we found that Japanese populations were strongly differentiated from the European populations (F(ST) = 0.416), more than expected by extrapolating the European pattern of IBD. Population structure analyses clearly separated the populations into two clusters, i.e. European and Japanese clusters. We discuss the possibility of IBD in a continuous population (considering some evidence for a ring species over the Northern Hemisphere) vs. an allopatric speciation over Eurasia, making L. amethystina a promising model of intercontinental species for future studies.

Evolutionary history of Serpulaceae (Basidiomycota): molecular phylogeny, historical biogeography and evidence for a single transition of nutritional mode

BACKGROUND

The fungal genus Serpula (Serpulaceae, Boletales) comprises several saprotrophic (brown rot) taxa, including the aggressive house-infecting dry rot fungus Serpula lacrymans. Recent phylogenetic analyses have indicated that the ectomycorrhiza forming genera Austropaxillus and Gymnopaxillus cluster within Serpula. In this study we use DNA sequence data to investigate phylogenetic relationships, historical biogeography of, and nutritional mode transitions in Serpulaceae.

RESULTS

Our results corroborate that the two ectomycorrhiza-forming genera, Austropaxillus and Gymnopaxillus, form a monophyletic group nested within the saprotrophic genus Serpula, and that the Serpula species S. lacrymans and S. himantioides constitute the sister group to the Austropaxillus-Gymnopaxillus clade. We found that both vicariance (Beringian) and long distance dispersal events are needed to explain the phylogeny and current distributions of taxa within Serpulaceae. Our results also show that the transition from brown rot to mycorrhiza has happened only once in a monophyletic Serpulaceae, probably between 50 and 22 million years before present.

CONCLUSIONS

This study supports the growing understanding that the same geographical barriers that limit plant- and animal dispersal also limit the spread of fungi, as a combination of vicariance and long distance dispersal events are needed to explain the present patterns of distribution in Serpulaceae. Our results verify the transition from brown rot to ECM within Serpulaceae between 50 and 22 MyBP.

Tracking the evolutionary history of Cortinarius species in section Calochroi, with transoceanic disjunct distributions

Background

Cortinarius species in section Calochroi display local, clinal and circumboreal patterns of distribution across the Northern Hemisphere where these ectomycorrhizal fungi occur with host trees throughout their geographical range within a continent, or have disjunct intercontinental distributions, the origins of which are not understood. We inferred evolutionary histories of four species, 1) C. arcuatorum, 2) C. aureofulvus, 3) C. elegantior and 4) C. napus, from populations distributed throughout the Old World, and portions of the New World (Central- and North America) based on genetic variation of 154 haplotype internal transcribed spacer (ITS) sequences from 83 population samples. By describing the population structure of these species across their geographical distribution, we attempt to identify their historical migration and patterns of diversification.

Results

Models of population structure from nested clade, demographic and coalescent-based analyses revealed genetically differentiated and geographically structured haplotypes in C. arcuatorum and C. elegantior, while C. aureofulvus showed considerably less population structure and C. napus lacked sufficient genetic differentiation to resolve any population structure. Disjunct populations within C. arcuatorum, C. aureofulvus and C. elegantior show little or no morphological differentiation, whereas in C. napus there is a high level of homoplasy and phenotypic plasticity for veil and lamellae colour. The ITS sequences of the type specimens of C. albobrunnoides and C. albobrunnoides var. violaceovelatus were identical to one another and are treated as one species with a wider range of geographic distribution under C. napus.

Conclusions

Our results indicate that each of the Calochroi species has undergone a relatively independent evolutionary history, hypothesised as follows: 1) a widely distributed ancestral population of C. arcuatorum diverged into distinctive sympatric populations in the New World; 2) two divergent lineages in C. elegantior gave rise to the New World and Old World haplotypes, respectively; and 3) the low levels of genetic divergence within C. aureofulvus and C. napus may be the result of more recent demographic population expansions. The scenario of migration via the Bering Land Bridge provides the most probable explanation for contemporaneous disjunct geographic distributions of these species, but it does not offer an explanation for the low degree of genetic divergence between populations of C. aureofulvus and C. napus. Our findings are mostly consistent with the designation of New World allopatric populations as separate species from the European counterpart species C. arcuatorum and C. elegantior. We propose the synonymy of C. albobrunnoides, C. albobrunnoides var. violaceovelatus and C. subpurpureophyllus var. sulphureovelatus with C. napus. The results also reinforce previous observations that linked C. arcuatorum and C. aureofulvus displaying distributions in parts of North America and Europe. Interpretations of the population structure of these fungi suggest that host tree history has heavily influenced their modern distributions; however, the complex issues related to co-migration of these fungi with their tree hosts remain unclear at this time.

Population genetics of ectomycorrhizal fungi: from current knowledge to emerging directions

Ectomycorrhizal (EM) fungi are major microbial components of boreal, temperate and Mediterranean forests, as well as some tropical forest ecosystems. Nearly two decades of studies have clarified many aspects of their population biology, based on several model species from diverse lineages of fungi where the EM symbiosis evolved, i.e. among Hymenomycetes and, to a lesser extent, among Ascomycetes. In this review, we show how tools for individual recognition have changed, shifting from the use of somatic incompatibility reactions to dominant and non-specific markers (such as random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP)) and, more recently, to co-dominant and specific markers (such as microsatellites and single nucleotide polymorphisms (SNPs)). At the same time, the theoretical focus has also changed. In earlier studies, a major aim was the description of genet size and popul/ation strategy. For example, we show how some studies supported or challenged the simple, classical model of colonization of new forest stands by ruderal (R) species, propagating by spores and forming small genets, progressively replaced in older forests by more competitive (C) species, propagating by mycelial growth and forming larger genets. By contrast, more recent studies give insights into some genetic traits, such as partners' assortment (allo- versus autogamy), genetic structure of populations and gene flow that turn out to depend both on distance and on whether spores are animal- or wind-dispersed. We discuss the rising awareness that (i) many morphospecies contain cryptic biological species (often sympatric) and (ii) trans- and inter-continental species may often contain several biological species isolated by distance. Finally, we show the emergence of biogeographic approaches and call for some aspects to be developed, such as fine-scale and long-term population monitoring, analyses of subterranean populations of extra-radical mycelia, or more model species from the tropics, as well as from the Ascomycetes (whose genetic idiosyncrasies are discussed). With the rise of the '-omics' sciences, analysis of population structure for non-neutral genes is expected to develop, and forest management and conservation biology will probably profit from published and expected work.

Inocybe tauensis, a new species from the Samoan Archipelago with biogeographic evidence for a Paleotropical origin

Inocybe tauensis is described as a new species from the island of Ta'u, American Samoa. The species occurs in native littoral forest and is associated with the ectomycorrhizal tree Pisonia grandis. Based on an analysis of nLSU, RPB1, and RPB2 sequence data, I. tauensis appears to be derived from ancestors with a Paleotropical biogeographical distribution. Alternative explanations for the unexpected presence of an Inocybe species in the Samoan Archipelago are discussed.

Bolete diversity in two relict forests of the Mexican beech (Fagus grandifolia var. mexicana; Fagaceae)

The current distribution of the endangered Mexican beech [Fagus grandifolia var. mexicana (Martinez) Little] is restricted to relict isolated populations in small remnants of montane cloud forest in northeastern Mexico, and little is known about its associated biota. We sampled bolete diversity in two of these monospecific forests in the state of Hidalgo, Mexico. We compared alpha diversity, including species richness and ensemble structure, and analyzed beta diversity (dissimilarity in species composition) between forests. We found 26 bolete species, five of which are probably new. Species diversity and evenness were similar between forests. Beta diversity was low, and the similarities of bolete samples from within and between forests were not significantly different. These results support the idea that the two forests share a single bolete ensemble with a common history. In contrast, cumulative species richness differed between the forests, implying that factors other than the mere presence of the host species have contributed to shaping the biodiversity of ectomycorrhizal fungi in relict Mexican beech forests.

Tuberculate ectomycorrhizae of angiosperms: The interaction between Boletus rubropunctus (Boletaceae) and Quercus species (Fagaceae) in the United States and Mexico

Tuberculate ectomycorrhizae (TECM) are unique structures in which aggregates of ectomycorrhizal roots are encased in a covering of fungal hyphae. The function of TECM is unknown, but they probably enhance the nitrogen nutrition and disease resistance of host plants. Trees in the Pinaceae form TECM with species of Rhizopogon and Suillus (Suillineae, Boletales). Similar tubercules are found with diverse angiosperms, but their mycobionts have not been phylogenetically characterized. We collected TECM in Mexico and the USA that were similar to TECM in previous reports. We describe these TECM and identify both the plant and fungal symbionts. Plant DNA confirms that TECM hosts are Quercus species. ITS sequences from tubercules and sclerotia (hyphal aggregations that serve as survival structures) matched sporocarps of Boletus rubropunctus. Phylogenetic analyses confirm that this fungus belongs to the suborder Boletineae (Boletales). This is the first published report of TECM formation in the Boletineae and of sclerotia formation by a Boletus species. Our data suggest that the TECM morphology is an adaptive feature that has evolved separately in two suborders of Boletales (Suillineae and Boletineae) and that TECM formation is controlled by the mycobiont because TECM are found on distantly related angiosperm and gymnosperm host plants.

Phylogeography and biogeography of fungi

The rigorous study of processes shaping geographic distributions of lineages is a relatively new and emerging field in mycology. While it was previously generally believed that most fungi have wide distributions and largely unstructured populations, recent studies have shown that this is not the case. The study of distributions in tandem with molecular approaches to phylogeny has recently made substantial advances to our understanding of the diversity and biogeography of fungi. Comprehensive species inventories have provided a better picture of the actual distribution of these organisms, while robust phylogenies based on molecular characters have provided both data that allow interpretation of current distributions and testable hypotheses regarding the processes responsible for distribution patterns. This commentary provides an introduction to five papers in this issue of Mycological Research that focus on fungal phylogeography. These papers are based on oral contributions given at two symposia at the International Mycological Congress (IMC8) held in Cairns (Australia) in August 2006.