Dispersal of Arbuscular Mycorrhizal Fungi: Evidence and Insights for Ecological Studies.

Dispersal is a critical ecological process that modulates gene flow and contributes to the maintenance of genetic and taxonomic diversity within ecosystems. Despite an increasing global understanding of the arbuscular mycorrhizal (AM) fungal diversity, distribution and prevalence in different biomes, we have largely ignored the main dispersal mechanisms of these organisms. To provide a geographical and scientific overview of the available data, we systematically searched for the direct evidence on the AM fungal dispersal agents (abiotic and biotic) and different propagule types (i.e. spores, extraradical hyphae or colonized root fragments). We show that the available data (37 articles) on AM fungal dispersal originates mostly from North America, from temperate ecosystems, from biotic dispersal agents (small mammals) and AM fungal spores as propagule type. Much lesser evidence exists from South American, Asian and African tropical systems and other dispersers such as large-bodied birds and mammals and non-spore propagule types. We did not find strong evidence that spore size varies across dispersal agents, but wind and large animals seem to be more efficient dispersers. However, the data is still too scarce to draw firm conclusions from this finding. We further discuss and propose critical research questions and potential approaches to advance the understanding of the ecology of AM fungi dispersal.

New species of Tulasnella associated with Australian terrestrial orchids in the Cryptostylidinae and Drakaeinae.

Many orchids have an obligate relationship with Tulasnella mycorrhizal fungi for seed germination and support into adulthood. Despite the importance of Tulasnella as mycorrhizal partners, many species remain undescribed. Here, we use multiple sequence locus phylogenetic analyses to delimit and describe six new Tulasnella species associated with Australian terrestrial orchids from the subtribes Cryptostylidinae and Drakaeinae. Five of the new species, Tulasnella australiensis, T. occidentalis, T. punctata, T. densa, and T. concentrica, all associate with Cryptostylis (Cryptostylidinae), whereas T. rosea associates with Spiculaea ciliata (Drakaeinae). Isolates representing T. australiensis were previously also reported in association with Arthrochilus (Drakaeinae). All newly described Tulasnella species were delimited by phylogenetic analyses of four loci (nuc rDNA internal transcribed spacer region ITS1-5.8S-ITS2 [ITS], C14436 [ATP synthase], C4102 [glutamate synthase], and mt 16S rDNA [mtLSU]). The pairwise sequence divergence between species for the ITS region ranged from 5.6% to 25.2%, and the maximum sequence divergence within the newly described species ranged from 1.64% to 4.97%. There was a gap in the distribution of within- and between-species pairwise divergences in the region of 4-6%, with only one within-species value of 4.97% (for two T. australiensis isolates) and one between-species value of 5.6% (involving an isolate of T. occidentalis) falling within this region. Based on fluorescence staining, all six new Tulasnella species are binucleate and have septate, cylindrical hyphae. There was some subtle variation in culture morphology, but colony diameter as measured on 3MN+vitamin medium after 6 wk of growth did not differ among species. However, T. australiensis grew significantly (P < 0.02) slower than others on ½ FIM and » potato dextrose agar (PDA) media. Formal description of these Tulasnella species contributes significantly to documentation of Tulasnella diversity and provides names and delimitations to underpin further research on the fungi and their relationships with orchids.

Glomus ibericum, Septoglomus mediterraneum, and Funneliformis pilosus, three new species of arbuscular mycorrhizal fungi.

Three new arbuscular mycorrhizal fungal species-Glomus ibericum, Septoglomus mediterraneum, and Funneliformis pilosus-are described and illustrated. In the field, the three species were associated with roots of Ammophila arenaria (Poaceae), Elymus farctus (Poaceae), Otanthus maritimus (Asteraceae), and Echinophora spinosa (Apiaceae) colonizing maritime dunes located along the Mediterranean coast in eastern Spain. The novelty of these species is supported by morphological, molecular, and phylogenetic analyses. Single-species cultures of S. mediterraneum and F. pilosus were obtained using Trifolium repens as a host plant, both forming arbuscular mycorrhizae, whereas single-species cultures from G. ibericum could not be obtained. Spores of G. ibericum usually occur in sporocarps, rarely singly in soil or inside roots. In contrast, S. mediterraneum only forms single spores in soil and F. pilosus occurs in sporocarps and singly in soil or inside roots. The respective small subunit, internal transcribed spacer, and large subunit (SSU-ITS1-5.8S-ITS2-LSU) nrDNA sequences placed the new species in the genera Glomus, Septoglomus, and Funneliformis, all of them separated from previously described species.

Isolation and Culture of Arbuscular Mycorrhizal Fungi from Field Samples.

The isolation of arbuscular mycorrhizal fungi from different land use is the starting point for selecting and producing inoculants. There are different techniques to isolate and produce large-scale arbuscular mycorrhizal fungi-based inoculum, being soil, inert substrate, and in vitro culture techniques among the most used by different biofertilizer producers. This chapter describes an active operating method to isolate and produce large-scale fungal inoculant in substrate-based manufacturing. In addition, critical parameters are presented for the optimal production of arbuscular mycorrhizal fungal inoculum. All the steps of the process are enlisted: from choosing the source of inoculum, its production, scaling, sustaining quality control, to shelf life.

A Whole-Plant Culture Method to Study Structural and Functional Traits of Extraradical Mycelium.

An in vivo whole-plant bi-dimensional experimental system has been devised and tested with different host plants, in order to obtain extraradical mycelium (ERM) produced by different arbuscular mycorrhizal fungi (AMF). In this system, a host plant germling is inoculated with AMF to establish mycorrhizal symbiosis, and, after colonization, newly formed extraradical hyphae and spores are removed. Then the mycorrhizal root system is wrapped in a nylon net and placed between membranes in a Petri dish, allowing ERM to grow on the membrane surface. Such extraradical hyphae may be used for in situ morphometric analyses or collected for molecular or biochemical assays: in the latter case, the plant with its root sandwich may be reassembled to renew mycelium production. In this experimental system, which was tested with diverse host plant species and lines, values of explored membrane surface areas and densities of ERM showed wide ranges of variation, and its length ranged from 9.7 ± 2.0 to 48.8 ± 9.9 m per plant, depending on host and AMF identity. Across the different plant-AMF combinations tested, the whole-plant system produced 2.0 ± 0.6 to 5.3 ± 0.3 mg of ERM fresh biomass per plant per harvest. This experimental system can be used for a wide range of AMF and host plants species, either establishing arbuscular mycorrhizas or other mycorrhizal interactions. ERM produced and collected in the whole-plant system is suitable for morphological, physiological, and molecular analyses, facilitating studies on the different aspects of mycorrhizal symbiotic interactions.

Histochemical Staining and Quantification of Arbuscular Mycorrhizal Fungal Colonization.

Histochemical staining and light microscopy-based techniques have been widely used to detect and quantify arbuscular mycorrhizal fungi (AMF) in roots. Here we describe a standardized method for staining of AMF in colonized roots, and we provide possible modifications to adjust the protocol according to particular requirements, such as the type of root material or the reduction of toxic products. In addition, we also summarize some of the most common ways to quantify arbuscular mycorrhizal colonization.

Revision of leccinoid fungi, with emphasis on North American taxa, based on molecular and morphological data.

The leccinoid fungi are boletes and related sequestrate mushrooms (Boletaceae, Basidiomycota) that have traditionally been placed in Leccinum, Boletus, Leccinellum, and a handful of other less familiar genera. These mushrooms generally feature scabers or scaber-like dots on the surface of the stipe, and they are often fairly tall and slender when compared with other boletes. They are ectomycorrhizal fungi and appear to be fairly strictly associated with specific trees or groups of related trees. In the present study, we investigate the phylogenetic relationships among the leccinoid fungi and other members of the family Boletaceae using portions of three loci from nuc 28S rDNA (28S), translation elongation factor 1-α (TEF1), and the RNA polymerase II second-largest subunit (RPB2). Two DNA data sets (combined 28S-TEF1 and 28S-TEF1-RPB2), comprising sequences from nearly 270 voucher specimens, were evaluated using two different phylogenetic analyses (maximum likelihood and Bayesian inference). Five major clades were obtained, and leccinoid fungi appeared in four of them. Taxonomic proposals supported by our results, representing a broadly circumscribed Leccinum that includes several sequestrate genera, along with Leccinellum, are made.

Nodulose-spored Inocybe from the Rocky Mountain alpine zone molecularly linked to European and type specimens.

Inocybe (Inocybaceae) is one of the most diverse ectomycorrhizal genera in arctic and alpine habitats where the primary hosts are Salix, Betula, and Dryas. Subgenus Inocybe is common in these habitats and typically characterized by the presence of thick-walled pleurocystidia. Here, we focus on species that have angular or nodulose spores. Historically, over 30 taxa from this group have been reported from arctic and alpine habitats. Many names have been synonymized, whereas molecular analysis has revealed new species. Nuc rDNA internal transcribed spacer ITS1-5.8S-ITS2 (ITS) sequence data of 26 type specimens in this group now allow for further taxonomic clarification and comparison across continents of disjunct populations. Here, we compare ITS sequence data and the D1-D2 portion of nuc 28S rDNA (28S) from Rocky Mountain specimens with those of types and European reference material. We report 10 species from the Rocky Mountain alpine zone, all of which are conspecific with known European boreal, montane, or alpine species, and four are described as new; all have intercontinental distributions. Nodulose-spored Inocybe taxa that occur in the Rocky Mountain alpine zone include I. alpinomarginata, sp. nov., I. arctica, I. giacomi, I. leonina, I. murina, sp. nov., I. occulta, I. paragiacomi, sp. nov., I. phaeocystidiosa, I. purpureobadia, and I. subgiacomi, sp. nov. Remarkably, these species occur at elevations up to 4000 m and at latitudes as low as 36°N, hundreds of miles from the Arctic, the European alpine, and original type localities. Distributions are explained in part by host distributions and historical glaciation patterns. A key and full descriptions for Rocky mountain species are provided to promote species recognition.

Septoglomus mexicanum, a new species of arbuscular mycorrhizal fungi from semiarid regions in Mexico.

Septoglomus mexicanum is here described as a new species of arbuscular mycorrhizal fungi (AMF; Glomeromycota) based on morphological and phylogenetic analyses. It was isolated from rhizospheric soil of two endemic Mexican legumes: Prosopis laevigata and Mimosa luisana, which grow in semiarid regions of central Mexico. Septoglomus mexicanum is characterized by forming globose spores of (154.5-)202.8(-228.9) µm diam and a spore wall consisting of four layers (SWL1-SWL4): outer wall layer (SWL1) hyaline, evanescent, (1.7-)3.2(-4.3) µm thick; SWL2 laminate and smooth, orange to reddish orange, (3.1-)4.5(-6.1) µm thick; SWL3 laminate, smooth, reddish orange to reddish brown, (4.1-)5.1(-5.7) µm thick; and SWL4 hyaline, semiflexible, (0.93-)1.2(-1.4) µm thick. None of the spore wall layers stain with Melzer's reagent. The subtending hypha has a color from yellowish to golden and presents a septum on spore base. Septoglomus mexicanum can be distinguished from all other Septoglomus species by spore size and color, by spore wall structure (four layers), and by color change of the subtending hypha. Phylogenetic analysis based on the AMF extended DNA barcode covering a 1.5-kb fragment of the small subunit (SSU), internal transcribed spacer region (ITS1-5.8S-ITS2), and the large subunit (LSU) of rRNA genes places S. mexicanum in the genus Septoglomus, separated from other described Septoglomus species, especially S. turnauae, with whom it could be confused morphologically. All available sequences in public databases suggest that this new fungal species has not yet been previously detected. Thus, there are currently 149 Glomeromycota species registered in Mexico, representing 47.4% of the known species worldwide.

A Medicago truncatula SWEET transporter implicated in arbuscule maintenance during arbuscular mycorrhizal symbiosis.

Plants form a mutualistic symbiosis with arbuscular mycorrhizal (AM) fungi, which facilitates the acquisition of scarce minerals from the soil. In return, the host plants provide sugars and lipids to its fungal partner. However, the mechanism by which the AM fungi obtain sugars from the plant has remained elusive. In this study we investigated the role of potential SWEET family sugar exporters in AM symbiosis in Medicago truncatula. We show that M. truncatula SWEET1b transporter is strongly upregulated in arbuscule-containing cells compared to roots and localizes to the peri-arbuscular membrane, across which nutrient exchange takes place. Heterologous expression of MtSWEET1b in a yeast hexose transport mutant showed that it mainly transports glucose. Overexpression of MtSWEET1b in M. truncatula roots promoted the growth of intraradical mycelium during AM symbiosis. Surprisingly, two independent Mtsweet1b mutants, which are predicted to produce truncated protein variants impaired in glucose transport, exhibited no significant defects in AM symbiosis. However, arbuscule-specific overexpression of MtSWEET1bY57A/G58D , which are considered to act in a dominant-negative manner, resulted in enhanced collapse of arbuscules. Taken together, our results reveal a (redundant) role for MtSWEET1b in the transport of glucose across the peri-arbuscular membrane to maintain arbuscules for a healthy mutually beneficial symbiosis.

The role of in vitro cultivation on asymbiotic trait variation in a single species of arbuscular mycorrhizal fungus.

Cultivating arbuscular mycorrhizal (AM) fungi in vitro is an efficient way to produce material for industry and research. However, such artificial growing conditions may impose selective pressure on fungi grown in vitro over many generations. We hypothesized that isolates subjected to long term propagation in vitro may develop increasingly ruderal traits. We proposed a predictive framework for the effect of in vitro cultivation on asymbiotic AM fungal traits. Using photomicrography and image processing, we analyzed morphology and growth traits for 14 isolates representing an in vitro cultivation gradient from 0 to >80 generations in vitro. We investigated the range of trait variation among asymbiotic growth of arbuscular mycorrhizal (AM) fungus isolates (Rhizoglomus irregulare). Spore dormancy was strongly associated with in vitro cultivation. We observed extremely high levels of inter-isolate variation for most fungal traits, but this was not related to time in vitro. Our results indicate that intra-specific diversity may have a strong ecological role in AM fungal communities.

Arbuscular cell invasion coincides with extracellular vesicles and membrane tubules.

During establishment of arbuscular mycorrhizal symbioses, fungal hyphae invade root cells producing transient tree-like structures, the arbuscules, where exchange of photosynthates for soil minerals occurs. Arbuscule formation and collapse lead to rapid production and degradation of plant and fungal membranes, their spatiotemporal dynamics directly influencing nutrient exchange. We determined the ultra-structural details of both membrane surfaces and the interstitial apoplastic matrix by transmission electron microscopy tomography during growth and senescence of Rhizophagus irregularis arbuscules in rice. Invasive growth of arbuscular hyphae was associated with abundant fungal membrane tubules (memtubs) and plant peri-arbuscular membrane evaginations. Similarly, the phylogenetically distant arbuscular mycorrhizal fungus, Gigaspora rosea, and the fungal maize pathogen, Ustilago maydis, developed memtubs while invading host cells, revealing structural commonalities independent of the mutualistic or parasitic outcome of the interaction. Additionally, extracellular vesicles formed continuously in the peri-arbuscular interface from arbuscule biogenesis to senescence, suggesting an involvement in inter-organismic signal and nutrient exchange throughout the arbuscule lifespan.

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.

A systematic revision of the ectomycorrhizal genus Laccaria from Korea.

Species of Laccaria (Hydnangiaceae, Basidiomycota) are important in forest ecosystems as ectomycorrhizal fungi. Nine of the 75 described Laccaria species worldwide been reported from Korea. Most of these have European and North American names, and their identities are based solely on morphological features. To evaluate the taxonomy of Korean Laccaria, we used 443 specimens collected between 1981 and 2016 in a phylogenetic analysis based on sequence data from nuc rDNA internal transcribed spacer ITS1-5.8S-ITS2 rDNA (ITS) region, nuc 28S rDNA (28S), RNA polymerase II subunit 2 (rpb2), and translation elongation factor 1-α (tef1). Ten Laccaria species were identified. Three of these were previously reported from Korea: L. bicolor, L. tortilis, and L. vinaceoavellanea. Laccaria alba, L. japonica, and L. murina are confirmed as new reports from Korea. Lastly, four new Laccaria species are described: L. araneosa, L. parva, L. torosa, and L. versiforma. This study supports the general contention that Asian species of ectomycorrhizal fungi may not be conspecific with morphologically similar species from Europe and North America. Furthermore, identification based on morphology alone is often unreliable in Laccaria due to considerable overlap of characters among species. Thus, use of molecular methods is necessary for effective identification. Illustrations of the four newly described species and a taxonomic key to species of Laccaria in Korea are provided.

Diversity and growth-effects of ectomycorrhizal fungi of a Nothofagus pumilio forest in the Andes of Southern Chile / (Diversidad y efectos de crecimiento de hongos ectomicorrízicos en un bosque de Nothofagus pumilio en los andes del sur de Chile

Chilean temperate rainforests have unique climatic, edaphic and biotic conditions, constituting pre-industrial blueprint ecosystems. Mycorrhizal associations play a central role in the biogeochemical processes of these ecosystems´ functioning. Baseline forest ecology studies are necessary in order to better understand diversity patterns, specifically regarding mycorrhizal symbiosis. Therefore, here we describe the vegetation characteristics and the mycorrhizal relationships of vascular plants in a Nothofagus pumilio forest. We also describe, via morphological methods, the ectomycorrhizal diversity present in this forest. Additionally, we determined whether ectomycorrhizal inoculation confers positive growth effects on N. pumilio seedlings. We found that from 46 vascular plant species identified in this study, 42 (91%) were mycorrhizal and of these 33 (72%) were associated with arbuscular mycorrhizae (AM), two (the dominant trees N. pumilio and N. dombeyi) were forming ectomycorrhizae (EM), five were associated with ericoid mycorrhizae, two with orchid mycorrhizae, and four were nonmycorrhizal. Additionally, 26 EM species were detected of which 15 belong to Cortinarius. Finally, there were clear differences in the growth of N. pumilio seedlings inoculated with the ectomycorrhizal fungus Laccaria laccata compared to noninoculated plants. We suggest that mycorrhizal fungi play a key role in seedling colonization of harsh environments such as the Andean treeline.

Los bosques templados lluviosos de Chile tienen condiciones climáticas, edáficas y bióticas únicas, constituyendo ecosistemas preindustriales modelo. Las asociaciones micorrízicas juegan un rol central en los procesos biogeoquímicos del funcionamiento de estos ecosistemas. Por lo tanto, en este estudio describimos las características de la vegetación y las relaciones micorrízicas de las plantas vasculares de un bosque de Nothofagus pumilio. También describimos, vía métodos morfológicos, la diversidad ectomicorrízica presente en este bosque. Adicionalmente, determinamos si inoculaciones ectomicorrízicas confieren efectos de crecimiento positivos a semilleros de N. pumilio. Encontramos que, de 46 especies de plantas vasculares identificadas en este estudio, 42 (91%) son micorrízicas, y de estas, 33 (72%) están formando micorrizas arbusculares (AM), dos (los árboles dominantes N. pumilio y N. dombeyi) están asociados con ectomicorrizas (EM), cinco están asociadas con micorrizas ericoides, dos con micorrizas orquioides, y cuatro fueron nomicorrizadas. Adicionalmente, 26 especies de EM fueron detectadas, de las cuales 15 pertenecen a Cortinarius. Finalmente, hubo claras diferencias en el crecimiento de los semilleros de N. pumilio inoculados con el hongo ectomicorrízico Laccaria laccata, comparados a plantas no inoculadas. Sugerimos que los hongos micorrízicos juegan un rol clave en la colonización de ambientes severos por juveniles, como en el límite altitudinal andino.

Fungal spore diversity reflects substrate-specific deposition challenges.

Sexual spores are important for the dispersal and population dynamics of fungi. They show remarkable morphological diversity, but the underlying forces driving spore evolution are poorly known. We investigated whether trophic status and substrate associations are associated with morphology in 787 macrofungal genera. We show that both spore size and ornamentation are associated with trophic specialization, so that large and ornamented spores are more probable in ectomycorrhizal than in saprotrophic genera. This suggests that spore ornamentation facilitates attachment to arthropod vectors, which ectomycorrhizal species may need to reach lower soil layers. Elongated spore shapes are more common in saprotrophic taxa, and genera associated with above ground substrates are more likely to have allantoid (curved elongated) spores, probably to lower the risk of wash out by precipitation. Overall, our results suggest that safe arrival on specific substrates is a more important driver of evolution in spore morphology than dispersal per se.

Arbuscular mycorrhizal fungi spore propagation using single spore as starter inoculum and a plant host.

AIMS: The propagation of pure cultures of arbuscular mycorrhizal fungal (AMF) is an essential requirement for their large-scale agricultural application and commercialization as biofertilizers. The present study aimed to propagate AMF using the single-spore inoculation technique and compare their propagation ability with the known reference spores. METHODS AND RESULTS: Arbuscular mycorrhizal fungal spores were collected from salt-affected Saemangeum reclaimed soil in South Korea. The technique involved inoculation of sorghum-sudangrass (Sorghum bicolor L.) seedlings with single, healthy spores on filter paper followed by the transfer of successfully colonized seedlings to 1-kg capacity pots containing sterilized soil. After the first plant cycle, the contents were transferred to 2·5-kg capacity pots containing sterilized soil. Among the 150 inoculated seedlings, only 27 seedlings were colonized by AMF spores. After 240 days, among the 27 seedlings, five inoculants resulted in the production of over 500 spores. The 18S rDNA sequencing of spores revealed that the spores produced through single-spore inoculation method belonged to Gigaspora margarita, Claroideoglomus lamellosum and Funneliformis mosseae. Furthermore, indigenous spore F. mosseae M-1 reported a higher spore count than the reference spores. CONCLUSIONS: The AMF spores produced using the single-spore inoculation technique may serve as potential bio-inoculants with an advantage of being more readily adopted by farmers due to the lack of requirement of a skilled technique in spore propagation. SIGNIFICANCE AND IMPACT OF THE STUDY: The results of the current study describe the feasible and cost-effective method to mass produce AMF spores for large-scale application. The AMF spores obtained from this method can effectively colonize plant roots and may be easily introduced to the new environment.

A new genus, Planticonsortium (Mucoromycotina), and new combination (P. tenue), for the fine root endophyte, Glomus tenue (basionym Rhizophagus tenuis).

In 1977, the fine root endophyte, originally named Rhizophagus tenuis, was transferred into the genus Glomus as G. tenue, thus positioning the species with all other known arbuscular mycorrhizal fungi (Glomeromycota, Glomeromycotina). Recent molecular evidence, however, places it in a different subphylum, Mucoromycotina in the Mucoromycota. No suitable genus exists in the Mucoromycotina to accommodate G. tenue, so it is moved to Planticonsortium gen. nov. as P. tenue comb. nov.

Cell-specific expression of plant nutrient transporter genes in orchid mycorrhizae.

Orchid mycorrhizal protocorms and roots are heterogeneous structures composed of different plant cell-types, where cells colonized by intracellular fungal coils (the pelotons) are close to non-colonized plant cells. Moreover, the fungal coils undergo rapid turnover inside the colonized cells, so that plant cells containing coils at different developmental stages can be observed in the same tissue section. Here, we have investigated by laser microdissection (LMD) the localization of specific plant gene transcripts in different cell-type populations collected from mycorrhizal protocorms and roots of the Mediterranean orchid Serapias vomeracea colonized by Tulasnella calospora. RNAs extracted from the different cell-type populations have been used to study plant gene expression, focusing on genes potentially involved in N uptake and transport and previously identified as up-regulated in symbiotic protocorms. Results clearly showed that some plant N transporters are differentially expressed in cells containing fungal coils at different developmental stages, as well as in non-colonized cells, and allowed the identification of new functional markers associated to coil-containing cells.

Unique phylogenetic position of the African truffle-like fungus, Octaviania ivoryana (Boletaceae, Boletales), and the proposal of a new genus, Afrocastellanoa.

The sequestrate (truffle-like) basidiomycete Octaviania ivoryana was originally described based on collections from Zimbabwe, Kenya, Guinea, and Senegal. This species has basidiomes that stain blue-green and basidiospores with crowded spines that are characteristic of the genus Octaviania. However, O. ivoryana is the only Octaviania species described from sub-Saharan Africa, and the phylogenetic relationship of the species to other species of Octaviania sensu stricto has not been previously investigated. We examined the phylogenetic position of the isotype and paratype specimens of O. ivoryana based on two nuc rDNA loci-ITS1-5.8S-ITS2 (internal transcribed spacer [ITS]) and partial 28S-and the translation elongation factor 1-α gene. The resultant phylogenies indicate that O. ivoryana does not belong to Octaviania s. s. but instead forms a clade with the epigeous bolete genus, Porphyrellus sensu stricto (i.e., P. porphyrosporus and allies). The internal transcribed spacer phylogeny also recovers a monophyletic clade that includes sequences from O. ivoryana basidiomes as well as sequences from ectomycorrhizal root tips of Uapaca, Anthonotha, and assorted ectomycorrhizal Fabaceae species, suggesting that there is likely additional undescribed diversity within the lineage. We accordingly propose a new genus, Afrocastellanoa M.E. Sm. & Orihara, to accommodate the species O. ivoryana. Afrocastellanoa is morphologically distinct from Octaviania in the combination of a solid gleba, multilayered peridium, and the lack of distinct hymenium within the gleba. Our data suggest that the genus Afrocastellanoa is a unique sequestrate lineage with one described species and several undescribed species, all of which likely form ectomycorrhizas with African trees.