Multigene phylogeny and taxonomic revision of Atheliales s.l. : Reinstatement of three families and one new family, Lobuliciaceae fam.

Atheliales ( Agaricomycetes , Basidiomycota ) is an order mostly composed of corticioid fungi, containing roughly 100 described species in 20 genera. Members exhibit remarkable ecological diversity, including saprotrophs, ectomycorrhizal symbionts, facultative parasites of plants or lichens, and symbionts of termites. Ectomycorrhizal members are well known because they often form a major part of boreal and temperate fungal communities. However, Atheliales is generally understudied, and molecular data are scarce. Furthermore, the order is riddled with many taxonomic problems; some genera are non-monophyletic and several species have been shown to be more closely related to other orders. We investigated the phylogenetic position of genera that are currently listed in Atheliales sensu lato by employing an Agaricomycetes -wide dataset with emphasis on Atheliales including the type species of genera therein. A phylogenetic analysis based on 5.8S, LSU, rpb2 , and tef1 (excluding third codon) retrieved Atheliales in subclass Agaricomycetidae , as sister to Lepidostromatales . In addition, a number of Atheliales genera were retrieved in other orders with strong support: Byssoporia in Russulales , Digitatispora in Agaricales , Hypochnella in Polyporales , Lyoathelia in Hymenochaetales , and Pteridomyces in Trechisporales . Based on this result, we assembled another dataset focusing on the clade with Atheliales sensu stricto and representatives from Lepidostromatales and Boletales as outgroups, based on ITS (ITS1 e 5.8S e ITS2), LSU, rpb2 , and tef1 . The reconstructed phylogeny of Atheliales returned ﬁ ve distinct lineages, which we propose here as families. Lobulicium , a monotypic genus with a distinct morphology of seven- lobed basidiospores, was placed as sister to the rest of Atheliales . A new family is proposed to accommodate this genus, Lobuliciaceae fam. nov . The remaining four lineages can be named following the family-level classi ﬁ cation by Jülich (1982), and thus we opted to use the names Atheliaceae , Byssocorticiaceae , Pilodermataceae , and Tylosporaceae , albeit with amended circumscriptions.

Most of the core Atheliales genera were initially grouped within Corticiaceae sensu lato (Donk, 1964). Parmasto (1968) then described the subfamily "Athelioideae" with three subsequent groups: "Atheliae", "Amylocorticieae", and "Byssomerulieae". Jülich (1972) published a monograph of "Atheliae" that contained core Atheliales genera such as Athelia, Byssocorticium, Fibulomyces, Leptosporomyces, Piloderma, and Tylospora. Subsequently, in his classification of basidiomycetes, Jülich (1982) introduced a family-level classification of the order Atheliales with four families: Atheliaceae, Byssocorticiaceae, Pilodermataceae, and Tylosporaceae. With the advent of molecular phylogenetics, Atheliales started to be included in large-scale studies (Boidin et al., 1998). In phylogenetic studies focusing on corticioid fungi, Larsson et al. (2004) and Binder et al. (2005) recovered Atheliales as a monophyletic group, which was later recognized as an order in the latest comprehensive classification of corticioid fungi (Larsson, 2007) and of the fungal kingdom , placed within the subclass Agaricomycetidae. With the limited sampling of Atheliales in these studies, Jülich (1982) subdivision into four families could not be tested and therefore only one family is currently recognized: Atheliaceae (He et al., 2019).
The relationship between Atheliales and Amylocorticiales, another order in Agaricomycetidae dominated by corticioid species, is still unclear. Based on phylogenomic studies (Li et al., 2020;Nagy et al., 2015), Atheliales is closely related with Amylocorticiales ( Fig. 1A). However, large-scale multigene phylogenies inferred from nuclear ribosomal SSU and LSU, 5.8S, rpb1, rpb2, and tef1 (Chen et al., 2019;Zhao et al., 2017) showed that Amylocorticiales is most closely related to Agaricales, while Atheliales is closely related to Lepidostromatales (Fig. 1B), for which no genomes are currently available. Varga et al. (2019) constructed a phylogeny of Agaricomycetes based on LSU, rpb2, and tef1 with a phylogenomic backbone constraint on the deep nodes, and Atheliales forms a clade with Amylocorticiales and Lepidostromatales with unresolved relationships (Fig. 1C).
Over the years, a number of genera have been described and added to Atheliales, based on morphological characters alone (Hjortstam andRyvarden, 2004, 2010) or combined with molecular phylogenetic evidence (Kotiranta et al., 2011). Sequence-based studies have found some of these genera to be polyphyletic, sometimes with members clustering within other orders (Binder et al., 2010;Ertz et al., 2008;Hibbett et al., 2007). Genera of Atheliales sensu lato are summarized in Table 1, as well as significant sources indicating their presumed affiliations. Well-annotated molecular data in public databases are scarce for Atheliales, and a phylogeny of the order is lacking.
In this study, we present the first comprehensive phylogenetic treatment of the order Atheliales with two specific aims. First, we aimed to delimit Atheliales by sampling the type species of the genera listed in Atheliales sensu lato (Table 1) as well as representatives of various orders within Agaricomycetes. Due to the taxonomic breadth of this analysis, we used molecular data from 5.8S and LSU of the nuclear ribosomal DNA as well as the protein coding regions of rpb2 and tef1 excluding the third codon position to reconstruct the phylogeny of Agaricomycetes. Second, we aimed to delineate phylogenetic lineages within the order. For this aim, we assembled a dataset composed of taxa belonging to Atheliales sensu stricto. This dataset was based on the nuclear ribosomal ITS1, 5.8S, ITS2, and LSU, as well as rpb2 and tef1 including the third codon position.

Taxon sampling, fungal isolates, and DNA extraction
We targeted taxa in Atheliales sensu lato as summarized in Table 1, with emphasis on the type species of each genus. Specimens were retrieved from the herbarium of Uppsala University Museum of Evolution (UPS), the herbarium of University of Gothenburg (GB), and the Farlow Herbarium at Harvard University (FH), as well as the private collections of B.P. Sulistyo (BPS) and M. Ryberg (MR) ( Table 2). Several specimens from GB (  B.P. Sulistyo, K.-H. Larsson, D. Haelewaters et al. Fungal Biology 125 (2021) 239e255 Norcross, GA) following the manufacturer's instructions. Specimens from UPS, BPS, and MR, as well as the rest of specimens from GB were extracted using a modified CTAB/chloroform-isoamyl alcohol DNA extraction (Cubero et al., 1999). Approximately 5 Â 5 mm hymenium was picked from the substrate and grinded using a micropestle in 500 ml of 2% CTAB extraction buffer (100 mL Tris, 20 mM Na 2 EDTA, 1.4 M NaCl, pH 8.0) with 1% b-mercaptoethanol.
The resulting mixture was then incubated at 65 C for up to 2 h.
Subsequently, 500 ml of chloroform: isoamyl alcohol (24:1) was added and the mixture was shaken horizontally at low speed for 1 h before centrifugation at 12,000 rpm for 14 min. Following this, 360 ml of the upper phase was transferred into a new tube and 240 ml of cold isopropanol was added. After the sample precipitated overnight at cold temperature, it was centrifuged and the resulting DNA pellet was washed using wash buffer (76% EtOH, 10 mM ammonium acetate). Finally, the DNA was dissolved in 50 ml TE buffer (10 mM Tris, 1 mM EDTA, pH 8.0), and its concentration and integrity were determined by means of Qubit Fluorometric Quantitation (Invitrogen, Carlsbad, CA) and gel electrophoresis.

PCR amplification, sequencing, and sequence analyses
Six molecular markers were used in this study: nuclear ribosomal regions of ITS1, 5.8S, ITS2, and LSU, as well as the protein coding regions of rpb2 and tef1 (Binder et al., 2010;Matheny et al., 2007;Miettinen et al., 2012;Zhao et al., 2017). Amplification of rpb2 targeted the region between conserved domains 5 and 7 (Liu et al., 1999), whereas for tef1 the target region was between exons 4 and 8 (Wendland and Kothe, 1997). Primers used for PCR and sequencing of these target regions are listed in Table 3. Modifications to two primers used in previous studies were also done to facilitate amplification and sequencing of Atheliales taxa. LB-W-R is a reverse-complement of LB-W (Tedersoo et al., 2008), used to bridge the gap in the sequencing of LSU PCR products. Additionally, EF1-1577Fa was based on EF1-1577F (Rehner and Buckley, 2005) with one nucleotide difference for better priming in Atheliales, and this primer was designed using the dataset of Binder et al. (2010).
Cycling conditions for the amplification of ITS began with initial denaturation at 95 C for 3 min, followed by 35e40 cycles of denaturation at 95 C for 15 s, annealing at 55 0 C for 30 s, and extension at 72 C for 1 min, concluded by final extension at 72 C for 10 min. LSU amplification used similar cycling conditions as ITS, but with annealing temperature of 48 C. Cycling conditions for the amplification of rpb2 and tef1 were based on the methods of Rehner and Buckley (2005) and Matheny et al. (2007). The program started with denaturation at 94 C for 2 min, 8 cycles of denaturation at 94 C for 40 s, annealing at 60 C for 40 s with 1 C decrease/cycle, and extension at 72 C for 1e2 min, followed by 36 cycles of denaturation at 94 C for 45 s, annealing at 53 C for 90 s, and extension at 72 C for 1e2 min, concluded by final extension at 72 C for 10 min. All PCR products were cleaned by means of ExoSAP-IT (Applied Biosystems, Foster City, CA) and sent for sequencing to Macrogen Europe (Amsterdam, the Netherlands). Purification and sequencing of PCR products for samples obtained from FH were outsourced to Genewiz (South Plainfield, NJ). Sequencing reads were assembled, assessed, and edited using CodonCode Aligner (CodonCode Corporation, Centerville, MA) or Sequencher 4.10.1 (Gene Codes Corporation, Ann Arbor, MI). To confirm their identities and filter out contaminations, ITS sequences of all samples were blasted against the UNITE database ; https://unite.ut.ee/).

Dataset assembly and multiple sequence alignment
We constructed two datasets: an Agaricomycetes-wide dataset and an Atheliales sensu stricto dataset. The Agaricomycetes dataset Table 1 Overview of Atheliales-associated taxa. Plus (þ) indicates that the taxon belongs to Atheliales, minus (À) that it does not, and both (þ/À) suggests non-monophyly because members exist both inside and outside Atheliales. Question mark (?) indicates uncertain placement, while asterisk (*) marks that the name is treated as a synonym. Empty cell means that it was not treated in the study. Numbered columns indicate the source: [1]¼ (Jülich, 1982), [2]¼ (Larsson et al., 2004) Table 2 Species names, voucher information, GenBank accession numbers and references of taxa included in this study. Taxon in bold denotes type species of genera listed in Atheliales sensu lato. Taxon followed by an asterisk (*) indicates that it was placed in Atheliales sensu lato but placed elsewhere according to this study, double asterisks (**) indicates the opposite.  comprised representatives of each order in the class (except Hysterangiales and Geastrales in the Phallomycetidae), with Dacrymycetes as outgroup. This Agaricomycetes dataset was used to identify the members of Atheliales sensu stricto and to ascertain the phylogenetic position of several taxa that had not yet been considered in a phylogenetic context. Based on the result of this dataset's  In total, 108 sequences were newly generated during this study: 31 ITS, 32 LSU, 26 rpb2, and 19 tef1 sequences. These were supplemented with 310 sequences downloaded from NCBI GenBank for phylogenetic analyses. The complete list of taxa and GenBank accession numbers can be found in Table 2. For both datasets, taxa without LSU were excluded from subsequent analyses to avoid indistinguishable branches in the tree (Sanderson et al., 2010). The molecular markers for the Agaricomycetes dataset were LSU, 5.8S, rpb2, and tef1. The ITS regions (ITS1 and ITS2) were excluded from the Agaricomycetes dataset to avoid erroneous alignment due to the large numbers of indels (Tedersoo et al., 2018). Furthermore, we also excluded the third codon positions of both rpb2 and tef1 from the Agaricomycetes dataset since this position is prone to saturation under broad taxonomic range (Binder et al., 2010;Matheny et al., 2007). This finding was supported by preliminary analyses, which showed that the exclusion of third codon positions increased overall support values. However, the opposite was true for the Atheliales dataset due to its narrower taxonomic breadth; as a result, third codon positions were included in this dataset. All three ITS regions, ITS1, 5.8S, and ITS2, were also included in the Atheliales dataset since direct comparison suggested that they contained significant phylogenetic signals as marked by the change in overall support values.
Alignments and overall data management were done in Geneious v.10.2 (Biomatters, Auckland, New Zealand). Sequences were grouped according to their respective region and aligned separately. Full-length ITS1, 5.8S, and ITS2 regions were identified and separated using ITSx . Multiple sequence alignments were carried out using MAFFT v7.388 (Katoh et al., 2002;Katoh and Standley, 2013). LSU, rpb2, and tef1 were aligned using the MAFFT EeINSeI algorithm, whereas GeINSeI was used for aligning full-length 5.8S, ITS1, and ITS2 sequences. Afterwards, alignments were improved by realigning several challenging regions, manual adjustments, including trimming the ends of sequences and the removal of introns from rpb2 and tef1 alignments.
Input for PF2 was the concatenated alignment with user-defined data blocks for each region as well as each codon position for rpb2 and tef1 (only the 1st and 2nd for the Agaricomycetes dataset and all three for the Atheliales dataset), analyzed using the greedy algorithm (Lanfear et al., 2012) and based on Bayesian information criterion (BIC), with options for models according to those that are available in either RAxML or MrBayes. Consequently, phylogenetic analyses were done following the partitioning scheme and substitution model recommended by PF2 (Table 4).
For RAxML analyses, a phylogenetic tree was inferred through 1000 rapid bootstrap replicates. Since the specification of different models among partitions is not possible with RAxML, GTRGAMMA þ I was selected as it fitted most of the partitions. As for MrBayes analyses, the MrBayes block appended to the PF2 output was directly used to define the partitions as well as their respective substitution models, with independent estimation of substitution rate matrix, gamma shape parameter, transition/ transversion rate ratio, proportion of invariant sites, and character state frequencies for each partition. Each MrBayes analysis was performed with two separate runs and four chains for each run, for 100,000,000 generations with a stop rule based on max standard deviation of split frequencies below 0.01 and sampling of trees every 1000 generations. Tracer v1.7 (Rambaut et al., 2018)

Phylogenetic analyses of the Agaricomycetes dataset
Alignment statistics for the Agaricomycetes dataset are summarized in Table 5. The final concatenated alignment for the Agaricomycetes dataset contained 3254 total characters, 2841 of which were variable (87.30%), with mean coverage of 80.22%. Furthermore, based on subsequent RAxML searches the corresponding alignment contained 1997 distinct alignment patterns and a proportion of gaps and completely undetermined characters of 36.30%. Partitioned RAxML analyses resulted in the best scoring tree with a likelihood value of À42267.72. In addition to this, MrBayes analyses, which consisted of two runs, converged into a stable distribution with mean likelihood value of À42251.59 and À42253.66, respectively. There was no significant conflict between the RAxML and MrBayes analyses. The topology shown in Fig. 3 is based on the ML tree, with bootstrap (BS) support and posterior probability (PP) values from the BI consensus tree. To facilitate discussion, support values are mentioned in the text as (BS/PP).

Phylogenetic analyses of the Atheliales sensu stricto dataset
The Atheliales dataset consisted of 59 ingroup taxa and 11 outgroup taxa (2 Lepidostromatales and 9 Boletales taxa). Various alignment statistics for the Atheliales dataset are summarized in Table 5. The final concatenated alignment added up to 3713 total characters, 3130 of which were variable (84.30%), with mean coverage level of 71.85%. Based on successive RAxML searches, the alignment consisted of 2036 distinct alignment patterns with the proportion of gaps and completely undetermined characters of 40.53%. Partitioned RAxML analyses of the dataset yielded a final optimized likelihood value of À33904.79, whereas the two MrBayes runs each converged into a stable distribution with mean likelihood of À33449.37 and À33451.04, respectively. Similar to the Agaricomycetes dataset, the best tree from RAxML and the consensus tree from MrBayes analyses showed congruent topology without any strongly supported conflict. The reconstructed ML phylogeny of Atheliales is shown in Fig. 4 with ML BS and Bayesian PP values.
In the resulting Atheliales phylogeny (Fig. 4), Lobulicium occultum was placed as sister to the rest of Atheliales taxa, which formed a clade with relatively strong support (72/1.00). Because of its unique and isolated phylogenetic position in combination with a distinct spore morphology and ecology, we propose to place Lobulicium in a new family, Lobuliciaceae. Atheliales was further divided into four major clades with moderate to strong support,    with 2 or 4 sterigmata; basidiospores smooth or verruculose, globose, elliptic, cylindrical, or lobed, thin-to slightly thick-walled, never amyloid or dextrinoid, sometimes cyanophilous. Saprotrophic, ectomycorrhizal, or parasitic on plants and lichens. Confirmed genera: Amphinema, Athelia, Athelopsis, Byssocorticium, Fibulomyces, Leptosporomyces, Lobulicium, Piloderma, Tretomyces, Tylospora.
Here we confirm that all four families should be accepted and that a fifth family, Lobuliciaceae fam. nov., should be added. Athelopsis subinconspicua and Leptosporomyces raunkiaerii are currently left as Atheliales incertae sedis.
Athelia and Fibulomyces share a pellicular basidioma and basidia arranged in clusters (Eriksson andRyvarden, 1973, 1975). The decision to keep the two genera separate has been questioned (Eriksson and Ryvarden, 1973). Our analyses show that if the current concept of Athelia is to be maintained, then Fibulomyces must be reduced to synonomy. If, on the other hand, we want to keep Fibulomyces separate, then Athelia bombacina and Athelia singularis must be transferred to a new genus. Morphologically, A. bombacina, A singularis, and Fibulomyces mutabilis are united by their consistently clamped hyphae (Eriksson et al, 1978(Eriksson et al, , 1984Kunttu et al., 2016). Eriksson and Ryvarden (1973) stated that A. bombacina resembles F. mutabilis morphologically and even ecologically.
A. singularis, on the other hand, is morphologically closer to Athelia fibulata (Kunttu et al., 2016), which is phylogenetically further related (Fig. 4). More data are needed before taxonomic changes can be made.
A future circumscription of Athelia should include more related taxa as well as an effort to delimit the type species, Athelia epiphylla ( Fig. 2A). Eriksson and Ryvarden (1973) noted that A. epiphylla is a complex with a considerable variation in morphology and they admittedly adopted a wide species concept when treating the species for North Europe. Description: Basidiomata annual, resupinate, effused, soft, byssoid to membranous, easily detached, margin undifferentiated; hymenium smooth, continuous, white, blue or greenish blue; hyphal system monomitic, septa with or without clamps, hyphae thin-walled or slightly thick-walled, hyphal strands present or absent; cystidia absent; basidia clavate or pedunculate, with four sterigmata; basidiospores smooth, globose, elliptic or cylindrical, thin-or slightly thick-walled, neither amyloid, dextrinoid nor cyanophilous. Saprotrophic or ectomycorrhizal.
Remarks: Jülich (1982) included three genera in this family, beside the type genus also Byssoporia and Hypochnopsis. However, Byssoporia has its place near Albatrellus in Russulales (Bruns et al., 1998;Larsson, 2007;Smith et al., 2013), and Hypochnopsis is a synonym of Amaurodon and belongs to Thelephorales (Kõljalg, 1996). In addition to the type genus, Byssocorticiaceae now includes Athelopsis and Leptosporomyces, both of which are in need of revision as they are non-monophyletic. This has been shown in the present study as well as in previous work (Hodkinson et al., 2014;Larsson, 2007).
Athelopsis was introduced to accommodate four species with an Athelia-like basidioma but having pedunculate instead of clavate basidia (Parmasto, 1968). Of these four species, only the type, Athelopsis glaucina, remains. Several other species have subsequently been added to the genus but a great majority of them are probably placed elsewhere. In our Atheliales analysis, A. glaucina was placed as sister to the rest of Byssocorticiaceae with moderate ML support (50 < BS < 75) but strong PP support (Fig. 4). However, its placement seems to be unstable and affected by dataset composition, as it clustered with Athelia in the Agaricomycetes dataset with strong support (Fig. 3). More data is needed to ascertain its position within the Byssocorticiaceae. Jülich (1982) introduced Leptosporomyces to accommodate species with Athelia-like basidiomata but with short-cylindrical instead of clavate basidia. The genus was introduced with five species although subsequent additions have raised the number of species to 15 (He et al., 2019;Index Fungorum, 2020). For most of these, DNA sequences are currently not available. In our analyses, only the type species was retrieved in Byssocorticiaceae, whereas Leptosporomyces raunkiaeri was placed in a separate clade with Athelopsis subinconspicua, both currently ranked as Atheliales incertae sedis. support values noted above the branches as (BS/PP). Thickened species name denotes the type species of genera within Atheliales sensu lato, an asterisk (*) indicates that the corresponding taxon used to belong to Atheliales sensu lato, double asterisk (**) indicates that the taxon used to be placed outside of Atheliales. Arrow points to the clade corresponding to subclass Agaricomycetidae. Description: Basidiomata annual, resupinate, thin and soft, easily detached, margin very finely fibrillose; hymenium smooth, porulose, white; hyphal system monomitic, septa with clamps, hyphae thin-walled; cystidia absent; basidia small, clavate, with four sterigmata, basally clamped; basidiospores strongly lobed, neither amyloid, dextrinoid nor cyanophilous. Presumably saprotrophic on coniferous trees.
Remarks: Lobulicium is a monotypic genus and contains only L. occultum, a saprotrophic species that produces small pellicular fruiting bodies with a soft and loose hymenial construction, typical of most Atheliales members. However, it is notable for its peculiar basidiospores (Fig. 2C), which are strongly lobed but still bisymmetrical. Lobulicium occultum also has a specialized habitat, growing in the cracks formed when trunks of Abies or Picea are subjected to brown cubic-rot decay by Fomitopsis pinicola (Hjortstam and Larsson, 1982;Nord en et al., 1999). This habitat preference is somewhat similar to that of A. subinconspicua (Kotiranta and Saarenoksa, 2005). Despite always being associated with brown-rot, Lobulicium is very likely not performing brown-rot but rather feeds from organic molecules left by other organisms. This species could be an interesting candidate for genome sequencing, in relation to its nutritional mode. Description: Basidiomata annual, resupinate and effused or spathulate, soft, byssoid to membranous, margin undifferentiated; hymenium smooth, continuous or porulose, white, yellowish or olivaceous brown; hyphal system monomitic, septa with or without clamps, hyphal strands present or absent, subicular hyphae often with crystals; cystidia absent; basidia clavate, with 2e4 sterigmata; basidiospores smooth, subglobose to elliptic, slightly thick-walled, neither amyloid nor dextrinoid, slightly cyanophilous. Saprotrophic or ectomycorrhizal.
Genera: Piloderma, Tretomyces, Stereopsis vitellina. Remarks: Only one genus, Piloderma, was mentioned in the original description of this family (Jülich, 1982). Tretomyces lutescens, the type species of Tretomyces, was described as Byssocorticium lutescens in Eriksson and Ryvarden (1973), but shares micromorphological characters with Piloderma (Kotiranta et al., 2011). The major difference in relation to the original circumscription is the inclusion of Stereopsis vitellina, which produces stipitate stereoid fruiting bodies and thus deviates from all other species in Atheliales. The type species of Stereopsis (Stereopsis radicans) belongs to the order Stereopsidales, and is characterized by twospored basidia and spores that become slightly angular upon drying (Sj€ okvist et al, , 2014. These features are lacking in S. vitellina. In addition, S. vitellina becomes brittle upon drying (Eriksson et al., 1984) similar to most other Atheliales members, whereas S. radicans becomes tough (Reid, 1965).
In our phylogenetic analyses, Amphinema was not recovered as monophyletic (Fig. 4). Tylospora asterophora was placed between Amphinema byssoides (type) and Amphinema diadema, indicating that the latter species should be moved out of Amphinema. However, this arrangement was not strongly supported by either BS or PP, and thus more data are needed before any taxonomic changes are made. Additionally, Tylospora was also found to be nonmonophyletic in Tedersoo and Smith (2013).

Atheliales incertae sedis
Athelopsis subinconspicua (Litsch.) Jülich. Leptosporomyces raunkiaerii (M.P. Christ.) Jülich. Two species included in our analyses did not cluster with any of the recognized families. Athelopsis subinconspicua and Leptosporomyces raunkiaeri formed a strongly supported clade, which was also inferred in previous studies (Binder et al., 2010;Hodkinson et al., 2014;Liu et al., 2018). This clade seems to be closely related to the Pilodermataceae clade but this relationship was only supported by PP (Fig. 4). These two species are reported to be saprotrophic (Ambrosio et al., 2014;Kubartov a et al., 2012) but are morphologically rather different, which is obvious from their generic placement. It is doubtful that they should be united in the same genus. Leptosporomyces raunkiaeri is rather similar to the type of Leptosporomyces. It differs primarily by somewhat larger basidiospores and by growing on dead angiosperm leaves whereas Leptosporomyces galzinii is above all found on decaying conifer wood. Athelopsis subinconspicua has typical pedunculate basidia but is in other respects not so similar to A. glaucina, the type species of Athelopsis. We believe the classification on genus level should first be disentangled before a clade name on family level is introduced.

Discussion
The class-wide phylogeny (Fig. 3) of this study made it possible to circumscribe Atheliales sensu stricto. Each order included in this dataset received either strong support from both ML BS (!75) and Bayesian PP (!0.95), or moderate support from ML BS (50e74) and strong support by PP. The resulting topology of our four-locus Agaricomycetes dataset (Fig. 3) lacked support on several deep nodes, although it is largely congruent with previous studies (Binder et al., 2010;Chen et al., 2019;Hodkinson et al., 2014;Liu et al., 2018;Nagy et al., 2015;Sj€ okvist et al., 2014;Zhao et al., 2017). Atheliales was placed within Agaricomycetidae (96/1.00), as sister to Lepidostromatales, although only with strong support from PP. The AthelialeseLepidostromatales clade was placed as sister to Boletales with weak ML BS support but strong PP support. Close relationships among Atheliales, Boletales, and Lepidostromatales mirrors results of previous studies using similar sets of genes (Chen et al., 2019;Liu et al., 2018;Zhao et al., 2017). Unlike these studies, however, a sister relationship between Amylocorticiales and Agaricales was not recovered in our analyses (Fig. 3), further highlighting the uncertainty of the placement of this order.
Only two members of Atheliales (Fibulorhizoctonia sp. d anamorph of Athelia sp. d and Piloderma olivaceum) and five members of Amylocorticiales (Amylocorticium subincarnatum, Anomoloma albolutescens, Anomoporia bombycine, A. myceliosa, and Plicaturopsis crispa) have their genomes sequenced, while no genomes are available for any representative of Lepidostromatales according to JGI's MycoCosm (https://mycocosm.jgi.doe.gov/mycocosm/home, accessed 1 October 2020; Grigoriev et al., 2012). Compared to the number of genomes of Agaricales and Boletales (147 and 59, respectively), this number is very low. Future phylogenomic studies on the relationships among orders within Agaricomycetidae should focus on sampling more taxa from Amylocorticiales, Atheliales, and Lepidostromatales and carefully sort out the signal for different placements of Amylocorticiales.
Athelopsis and Leptosporomyces were found to be nonmonophyletic, and the monophyly of Amphinema, Athelia, and Piloderma was unsupported. This can probably be attributed to incomplete taxon sampling in combination with low molecular data coverage. Although previous studies have found members of Athelia, Athelopsis, and Leptosporomyces to be phylogenetically affiliated with other orders (Binder et al., 2010;Ertz et al., 2008;Larsson, 2007;Miettinen and Larsson, 2011), this study confirmed that their respective type species belong to Atheliales. Notwithstanding, revisions of these genera is necessary especially for Athelia, the type genus of the family. Corticioid fungi are particularly prone to misidentification (Binder et al., 2005). To minimize this problem, we used specimens that were identified by known experts of corticioid fungi. In addition, we utilized multiple collections for each species whenever possible. Future studies should build on this work by including type specimens.
Atheliales is a suitable group to study the evolutionary patterns of different nutritional modes because of the remarkable diversity observed within the group (Adams and Kropp, 1996;Matsuura et al., 2000;Stokland and Larsson, 2011;Tedersoo et al., 2010;Wenneker et al., 2017;Yurchenko and Olubkov, 2003). Atheliaceae is dominated by saprotrophic taxa, with one lichenicolous species (Athelia arachnoidea), while Byssocorticiaceae, Pilodermataceae, and Tylosporaceae are dominated by ectomycorrhizal taxa. Within Byssocorticiaceae, the earlier branching taxa (Athelopsis glaucina, L. galzinii, and Leptosporomyces sp.) are saprotrophic, which seemed to be the plesiomorphic state of the family. Although the overall relationships among taxa within Pilodermataceae are still lacking in support, this seems to also be the case within the family, as the earliest branching taxon likely is Stereopsis vitellina, a noncorticioid and reportedly saprotrophic species (Maaroufi et al., 2019). Tylosporaceae, on the other hand, seems to consist of strictly ectomycorrhizal species. However, our sampling only represents a fraction of the true Atheliales diversity, thus it is possible that Tylosporaceae also contains saprotrophic members. Based on our analyses, the earliest branching taxon in Atheliales is Lobulicium occultum, a saprotrophic species (Fig. 4). It is likely that the plesiomorphic state for nutrition in Atheliales is saprotrophic, and that ectomycorrhizal evolved multiple times in different groups. Ectomycorrhizal symbiosis arose several times from saprotrophic ancestors within fungi (Kohler et al., 2015;Tedersoo and Smith, 2013), as well as within smaller groups (S anchez-García and Matheny, 2017;Sato and Toju, 2019;Veldre et al., 2013). To make conclusive statements on the evolution nutritional modes, more data, better phylogenetic resolution on key nodes, and more comprehensive analyses of ancestral states are needed.
Compared with most other orders within Agaricomycetidae except Amylocorticiales, Atheliales is relatively understudied and undersampled (Rosenthal et al., 2017). It is possible that Atheliales contains undiscovered lineages. This gives hope to add taxa in the future that can break up long branches and pinpoint evolutionary relationships that are currently unresolved (e.g., the placement of A. subinconspicua and L. raunkiaeri, and the relationships among lineages). Additionally, the different placement of A. glaucina depending on the composition of the dataset and its relatively long branch, as well as the weakly-supported placement of the A. subinconspicuaeL. raunkiaeri clade suggest that these lineages might be composed of many more taxa.
The classification proposed here is only a first step in improving the taxonomy of Atheliales, and further refinement will be needed as more taxa will continue to be included in phylogenetic analyses. Future systematic studies of Atheliales should include genera of Atheliales s.l. that were not included in our study (Table 1): Athelicium, Athelocystis, Butlerelfia, Elaphocephala, Hypochniciellum, Melzericium, and Mycostigma.