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Research Article
Redelimitation of Heteroradulum (Auriculariales, Basidiomycota) with H. australiense sp. nov.
expand article infoQian-Zhu Li§|, Shi-Liang Liu|, Xue-Wei Wang§|, Tom W. May, Li-Wei Zhou|
‡ Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, China
§ University of Chinese Academy of Sciences, Beijing, China
| Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
¶ Royal Botanic Gardens Victoria, Melbourne, Australia
Open Access

Abstract

Auriculariales accommodates species with diverse basidiomes and hymenophores. From morphological and phylogenetic perspectives, we perform a taxonomic study on Heteroradulum, a recently validated genus within the Auriculariales. The genus Grammatus is merged into Heteroradulum, and thus its generic type G. labyrinthinus is combined with Heteroradulum and G. semis is reaccepted as a member of Heteroradulum. Heteroradulum australiense is newly described on the basis of three Australian specimens. Heteroradulum yunnanense is excluded from this genus and its taxonomic position at the generic level is considered uncertain. Accordingly, the circumscription of Heteroradulum is re-delimited and the concept of this genus is adjusted by including irpicoid to poroid hymenophores and a hyphal system with clamp connections or simple septa. A key to all nine accepted species of Heteroradulum is presented.

Keywords

Agaricomycetes, Australia, Grammatus, heterobasidiomycetes, two new taxa, wood-inhabiting fungi

Introduction

Auriculariales (Agaricomycetes, Basidiomycota) is characterized by a wood-inhabiting habit and longitudinally or transversely septate basidia (Weiß and Oberwinkler 2001). While the type genus Auricularia Bull. and a number of additional genera accommodate “jelly fungi” with gelatinous basidiomes, some other genera in this order have tough basidiomes with smooth, hydnoid, poroid or lamellate hymenophores (Weiß and Oberwinkler 2001; Zhou and Dai 2013; Malysheva and Spirin 2017; Malysheva et al. 2018). The diverse macromorphological characters result in the taxonomy of Auriculariales having rarely focused on the whole order. Therefore, within this order, the intergeneric relationships, viz. their taxonomic positions at the family level, are not clear; moreover, the independence and monophyly of certain genera still needs to be addressed (Zhou and Dai 2013; Malysheva and Spirin 2017).

Weiß and Oberwinkler (2001) performed the first comprehensive phylogenetic analysis of Auriculariales. The redefined Auriculariales was composed of five well supported groups, but the monophyly of this order even as represented by limited samples was not statistically supported (Weiß and Oberwinkler 2001). With this phylogenetic frame as a main reference, the taxonomy and phylogeny of poroid and lamellate species were further explored (Miettinen et al. 2012; Zhou and Dai 2013; Sotome et al. 2014; Wu et al. 2017; Spirin et al. 2019a). In addition, the knowledge of the diversity of species with gelatinous basidiomes has been extremely enriched recently (Bandara et al. 2015; Wu et al. 2015a, b; Malysheva et al. 2018; Spirin et al. 2018, 2019b; Chen et al. 2020; Ye et al. 2020; Wang and Thorn 2021).

On the basis of morphology, the non-gelatinous species of Auriculariales that are resupinate with or without a narrow reflexed pileus (i.e., corticioid or stereoid) have been placed in the genera Eichleriella Bres., Exidiopsis (Bref.) Möller and Heterochaete Pat. (Bodman 1952; Wells 1961; Wells and Raitviir 1977, 1980). Circumscriptions of the genera changed over time, but according to Wells and Raitviir (1977, 1980) the distinguishing character of Eichleriella was the presence of a basal layer of thick-walled, brown hyphae, while the delimitation of Heterochaete relied on the presence of minute, sterile spines (hyphal pegs) on the hymenophore. With the integration of molecular data into phylogenies including these and related genera, Hirneolina (Pat.) Bres. and Tremellochaete Raitv. have been reinstated and a number of novel genera have been introduced, including Adustochaete Alvarenga & K.H. Larss., Amphistereum Spirin & Malysheva, Crystallodon Alvarenga (Alvarenga and Gibertoni 2021), Heteroradulum Lloyd ex Spirin & Malysheva, Proterochaete Spirin & Malysheva and Sclerotrema Spirin & Malysheva (Malysheva and Spirin 2017; Alvarenga et al. 2019). After transfer of some species to these novel genera, Eichleriella (as far as sequenced species go) is monophyletic, but Exidiopsis is currently polyphyletic. The only species remaining in Heterochaete for which sequences are available is the type (H. andina Pat. & Lagerh.) and this is close to the type of Exidiopsis [E. effusa (Bref. ex Sacc.) Möller], leading Malysheva and Spirin (2017) to suggest that the two genera may be synonymous. Numerous species remain in Heterochaete that are yet to be sequenced, while those that have been sequenced, apart from H. andina, are placed in Crystallodon, Eichleriella and Heteroradulum.

Heteroradulum, typified by H. kmetii (Bres.) Spirin & Malysheva, was validated by Malysheva and Spirin (2017), who included seven species in this genus. Later, the new genus Grammatus H.S. Yuan & Decock was introduced, typified by G. labyrinthinus H.S. Yuan & Decock, and H. semis was transferred to Grammatus (Yuan et al. 2018). However, the phylogenetic analysis of Yuan et al. (2018) did not recover a monophyletic group for the remaining sampled species of Heteroradulum. Recently, Heteroradulum yunnanense C.L. Zhao (as ‘yunnanensis’) was newly described in Heteroradulum (Guan et al. 2020) but the phylogeny sampled only Heteroradulum as ingroup taxa and the analysis cannot properly determine whether H. yunnanense, which had a basal phylogenetic position, belongs to Heteroradulum or not. Therefore, questions remain about the delimitation of Heteroradulum from a phylogenetic perspective.

During field trips in Australia, three specimens bearing corticioid basidiomes and longitudinally septate basidia were collected. Based on these specimens, a new species of Heteroradulum was identified and is presented below along with a revised phylogeny of the genus and its relatives based on molecular data. This phylogenetic analysis leads to a revised circumscription of Heteroradulum.

Materials and methods

Morphological examination

The studied specimens are preserved at the Fungarium, Institute of Microbiology, Chinese Academy of Sciences (HMAS), Beijing, China and the National Herbarium of Victoria (MEL), Melbourne, Australia. The hymenial surfaces of basidiomes were observed and photographed with the aid of a stereomicroscope (LEICA M125). Special color terms follow Petersen (1996). Microscopic procedure followed Wang et al. (2020). A Nikon Eclipse 80i light microscope (Tokyo, Japan) was used at magnifications up to 1000×. Specimen sections were prepared with Cotton Blue (CB), Melzer’s reagent (IKI) and 5% potassium hydroxide (KOH) for observation. All measurements were taken from materials mounted in CB. Drawings were made with the aid of a drawing tube. When presenting the variation of basidiospore sizes, 5% of the measurements were excluded from each end of the range and are given in parentheses. The following abbreviations are used in the text: L = mean basidiospore length (arithmetic average of all measured basidiospores), W = mean basidiospore width (arithmetic average of all measured basidiospores), Q = variation in the L/W ratios between the specimens studied, and (a/b) = number of basidiospores (a) measured from given number (b) of specimens.

Molecular sequencing

Crude DNA was extracted from basidiomes of dry specimens using FH Plant DNA Kit (Beijing Demeter Biotech Co., Ltd., Beijing, China), and then directly used as template for subsequent PCR amplifications. The primer pairs ITS5/ITS4 (White et al. 1990) and LR0R/LR7 (Vilgalys and Hester 1990) were selected for amplifying the ITS and nLSU regions, respectively. The PCR procedures are as follows: for the ITS region, initial denaturation at 95 °C for 3 min, followed by 34 cycles at 94 °C for 40 s, 57.2 °C for 45 s and 72 °C for 1 min, and a final extension at 72 °C for 10 min, while for the nLSU region, initial denaturation at 94 °C for 1min, followed by 34 cycles at 94 °C for 30 s, 47.2 °C for 1 min and 72 °C for 1.5 min, and a final extension at 72 °C for 10 min. The PCR products were sequenced with the same primers as those used in amplifications at the Beijing Genomics Institute, Beijing, China. The newly generated sequences were deposited in GenBank (https://www.ncbi.nlm.nih.gov/genbank/; Table 1).

Table 1.

Information on species and specimens used in the phylogenetic analysis. The newly generated sequences are in boldface. Type specimens are indicated with an asterisk (*).

Species Voucher number GenBank accession number
ITS nLSU
Amphistereum leveilleanum FP-106715 KX262119 KX262168
A. schrenkii HHB8476 KX262130 KX262178
Aporpium hexagonoides ML297 AB871754 AB871735
Auricularia mesenterica FO25132 AF291271 AF291292
A. mesenterica TUFC12805 AB915192 AB915191
A. polytricha TUFC12920 AB871752 AB871733
Basidiodendron eyrei TUFC14484 AB871753 AB871734
Eichleriella bactriana TAAM55071* KX262121 KX262170
E. leucophaea LE303261 KX262111 KX262161
Elmerina caryae WD2207 AB871751 AB871730
E. foliacea Yuan 5691 JQ764666 JQ764644
E. hispida WD548 AB871768 AB871749
E701 AB871767 AB871748
Exidia glandulosa TUFC34008 AB871761 AB871742
E. glandulosa MW355 AF291273 AF291319
E. pithya MW313 AF291275 AF291321
Exidiopsis calcea MW331 AF291280 AF291326
E. effusa OM19136 KX262145 KX262193
E. grisea E. grisea RoKi162 AF291281 AF291328
TUFC100049 AB871765 AB871746
Exidia sp. TUFC34333 AB871764 AB871745
FO46291 AF291282 AF291329
Heteroradulum adnatum LR23453* KX262116 KX262165
H. australiense LWZ 20180512–20* MZ325254 MZ310424
LWZ 20180512–25* MZ325255 MZ310425
LWZ 20180515–26* MZ325256 MZ310426
H. deglubens FO12006 AF291272 AF291318
LE38182 KX262112 KX262162
LE225523 KX262113 KX262163
TAAM064782 KX262101 KX262148
Solheim1864 KX262133 KX262181
H. kmetii Kmet* KX262124 KX262173
VS8858 KX262105 KX262154
VS8864 KX262106 KX262155
VS8981 KX262132 KX262180
VS8988 KX262107 KX262156
LE38181 KX262109 KX262159
DAOM145605 KX262135 KX262183
DAOM31292 KX262134 KX262182
OF-295640 KX262122 KX262171
OF-295641 KX262117 KX262166
H. kmetii OF-295639 KX262128 KX262177
VS7967 KX262108 KX262157
TAAM9847 KX262125 KX262174
VS6466 KX262104 KX262152
LE303456 KX262103 KX262151
TAAM149179 KX262102 KX262149
CWU4563 KX262127 KX262176
CWU6152 KX262126 KX262175
LR14389 KX262131 KX262179
H. labyrinthinum Yuan 1759* KM379137 KM379138
Yuan 1600* KM379139 KM379140
H. semis OM10618* KX262146 KX262194
H. yunnanense CLZhao 4023* MT215568 MT215564
CLZhao 8106* MT215569 MT215565
CLZhao 9132* MT215570 MT215566
CLZhao 9200* MT215571 MT215567
Heteroradulum sp. USJ55639 AF291285 AF291336
Hirneolina hirneoloides USJ55480 AF291283 AF291334
Sclerotrema griseobrunneum VS7674 KX262140 KX262188
Sistotrema brinkmannii 236 JX535169 JX535170
Tremellochaete japonica LE303446 KX262110 KX262160

Phylogenetic analysis

Besides the newly sequenced specimens, additional taxa representing all main lineages within the Auriculariales were also included in the current phylogenetic analysis, and Sistotrema brinkmannii (Bres.) J. Erikss. within the Cantharellales was selected as an outgroup taxon following Malysheva and Spirin (2017) (Table 1). The datasets of ITS and nLSU regions were aligned separately using MAFFT version 7 (Katoh and Standley 2013) with the G-INS-i strategy (Katoh et al. 2005). Then, the two resulting alignments were concatenated as a single alignment for subsequent phylogenetic analysis. This alignment was submitted to TreeBASE (http://www.treebase.org; accession number S28342) and its best-fit evolutionary model was estimated using jModelTest (Guindon and Gascuel 2003; Posada 2008) with calculation under the Akaike information criterion. Following the resulting evolutionary model SYM + I + G, Maximum Likelihood (ML) and Bayesian Inference (BI) analyses were performed. The ML analysis was conducted using raxmlGUI 1.2 (Silvestro and Michalak 2012; Stamatakis 2006) with the calculation of bootstrap (BS) replicates under the auto FC option (Pattengale et al. 2010). The BI analysis was conducted using MrBayes 3.2 (Ronquist et al. 2012) with two independent runs, each including four chains of 10 million generations and starting from random trees. Trees were sampled every 1000th generation. The first 25% of the resulting trees was discarded as burn-in, while the remaining 75% were used for constructing a 50% majority consensus tree and calculating Bayesian posterior probabilities (BPPs). Chain convergence was determined using Tracer 1.5 (http://tree.bio.ed.ac.uk/software/tracer/).

Results

Three ITS and three nLSU sequences were newly generated from three Australian specimens of Heteroradulum for this study. The alignment used for phylogenetic analysis has 62 collections and 1583 characters. The ML analysis ended after 300 BS replicates. The BI analysis converged after 10 million generations as indicated by an average standard deviation of split frequencies = 0.004375, the effective sample sizes of all parameters above 4960 and the potential scale reduction factors equal to 1.000. The ML and BI analyses generated similar topologies in main lineages, and thus the topology generated from ML analysis is presented along with BS values above 50% and BPPs above 0.8 at the nodes (Figure 1).

Figure 1. 

Phylogenetic delimitation of Heteroradulum within the Auriculariales inferred from the combined dataset of ITS and nLSU regions. The topology generated by the maximum likelihood analysis is presented along with bootstrap values and Bayesian posterior probabilities above 50% and 0.8, respectively, at the nodes. The specimens of the newly described species are in boldface.

The current phylogeny groups Grammatus and Heteroradulum, with the exception of H. yunnanense, as a strongly supported clade (BS = 94%, BPP = 1; Figure 1). Within this clade, the three newly sequenced Australian specimens grouped as a fully supported lineage, as sister to the two species formerly placed in the genus Grammatus, forming a strongly supported subclade (BS = 92%, BPP = 1), while the monophyly of the subclade including the remaining species of Heteroradulum, viz. H. adnatum Spirin & Malysheva, H. deglubens (Berk. & Broome) Spirin & Malysheva and H. kmetii, did not receive reliable statistical support (Figure 1). This topology means that the subclades containing the types of Grammatus and Heteroradulum respectively are not reciprocally monophyletic within the strongly supported clade. Heteroradulum yunnanense falls outside of the Heteroradulum clade as a well-supported sister to a clade comprised of three taxa currently placed in Exidiopsis (Figure 1).

Taxonomy

Heteroradulum Lloyd ex Spirin & Malysheva, in Malysheva & Spirin, Fungal Biology 121(8): 709 (2017)

= Grammatus H.S. Yuan & Decock, in Yuan, Lu & Decock, MycoKeys 35: 32 (2018)

Remarks

Following the phylogenetic analysis, we treat Grammatus and Heteroradulum as a single genus, for which Heteroradulum has priority. The newly revealed Australian lineage is described as the new species Heteroradulum australiense below. In addition, G. labyrinthinus is combined to Heteroradulum and G. semis (Spirin & Malysheva) H.S. Yuan & Decock is reaccepted as a member of Heteroradulum.

Malysheva and Spirin (2017) defined the morphological characters of Heteroradulum according to the seven accepted species at that time, viz. H. adnatum, H. brasiliense (Bodman) Spirin & Malysheva, H. deglubens, H. kmetii, H. lividofuscum (Pat.) Spirin & Malysheva, H. semis and H. spinulosum (Berk. & M.A. Curtis) Spirin & Malysheva. The concept of this genus was adjusted by below including H. australiense with generative hyphae bearing a mixture of simple septa and clamp connections and H. labyrinthinus with irpicoid to poroid hymenophores.

Heteroradulum australiense L.W. Zhou, Q.Z. Li & S.L. Liu, sp. nov.

MycoBank No: 842485
Figures 2, 3

Etymology

australiense (Lat.), refers to Australia.

Type

Australia, Tasmania, Tahune Adventures, Arve River Picnic Area, on fallen angiosperm branch, 15 May 2018, L.W. Zhou, LWZ 20180515–26 (holotype in MEL, isotype in HMAS).

Figure 2. 

Basidiomes of Heteroradulum australiense. A–B LWZ 20180515–26 (holotype) C LWZ 20180512–20 (paratype) D LWZ 20180512–25 (paratype). Scale bars: 2 mm (A); 1 cm (B–D).

Diagnosis

Heteroradulum australiense differs from other species in this genus by the generative hyphae having a mixture of simple septa and clamp connections.

Figure 3. 

Microscopic structures of Heteroradulum australiense (drawn from the holotype, LWZ 20180515–26). A basidiospores B, C basidia and basidioles D cystidia E skeletocystidia F dendrohyphidia G hymenium H subicular hyphae. Scale bars: 10 μm (A–H).

Description

Basidiomes annual, resupinate, adnate, without odor or taste when fresh, leathery, covering 24.5 cm in widest dimension and up to 0.4 mm thick. Hymenophore odontioid, covered by irregularly arranged spines, up to 0.2 mm long, 3–5 per mm, pale red to reddish lilac when fresh, pale orange to brownish gray upon drying. Margin smooth, adnate, yellowish white, 0.5 mm wide.

Hyphal system dimitic; generative hyphae with simple septa or clamp connections; skeletal hyphae IKI–, CB+; tissue unchanged in KOH. Subicular generative hyphae hyaline, thin to thick-walled, rarely branched, 2–4 μm in diam; skeletal hyphae hyaline to brownish, thick-walled, interwoven, occasionally branched, 2.5–4 μm in diam, sometimes irregularly inflated up to 6 μm. Subhymenial generative hyphae hyaline to brownish, thin-to slightly thick-walled, 2–3.5 μm in diam; skeletal hyphae brownish, thick-walled, encrusted by grainy crystals, subparallel and vertical along substrate, compact, 2–4.5 μm in diam. Clavate to subcylindrical cystidia abundant, septate with or without clamp connections, thin-walled, 24–56 × 3–8 μm. Skeletocystidia present as endings of subicular skeletal hyphae, distinctly thick-walled, heavily encrusted by grainy crystals, 4–7 μm in diam. Dendrohyphidia abundant, scattered among hymenial cells, covering the hymenial surface, branched, up to 54 μm long, 2–3 μm in diam. Basidia narrowly ovoid to obconical, longitudinally septate, four-celled, 29–34.5 × 10–13.5 μm, with enucleate stalk up to 14 × 4 μm. Basidiospores cylindrical, slightly or distinctly curved, hyaline, thin-walled, smooth, occasionally with oily inclusions, IKI–, CB–, (14.5–)15–20(–20.5) × 5–7(–7.5) μm, L = 17.0 μm, W = 6.2 μm, Q = 2.66–2.88 (n = 90/3).

Specimens (paratypes) examined

Australia, Victoria, Yarra Ranges National Park, Dandenong Ranges Botanic Garden, on a fallen branch of Eucalyptus, 12 May 2018, L.W. Zhou, LWZ 20180512–20 (HMAS), on fallen angiosperm branch, 12 May 2018, L.W. Zhou, LWZ 20180512–25 (HMAS).

Remarks

Heteroradulum australiense is characterized by pale red to reddish lilac basidiomes, a dimitic hyphal system, generative hyphae with simple septa or clamp connections, abundant skeletocystidia in the hymenium, and basidia with an enucleate stalk. Heteroradulum kmetii and H. spinulosum resemble H. australiense by odontoid hymenophores, a dimitic hyphal system and the presence of skeletocystidia (Malysheva and Spirin 2017). However, H. kmetii has longer spines (up to 1 mm long) and slightly larger basidiospores (14.3–22.3 × 6–9.2 μm), and generative hyphae always with clamp connections; and H. spinulosum differs by basidia with a shorter enucleate stalk (up to 6 μm long) and generative hyphae always with clamp connections (Malysheva and Spirin 2017).

In regard to previously described Australian species against which H. australiense should be compared, the coriaceous, resupinate species of the Auriculariales are poorly sampled from Australia. May et al. (2003) listed records from Australia of a number of species of Eichleriella, Exidiopsis and Heterochaete that were originally described from the Northern Hemisphere. Such records remain suspect unless confirmed. Only two new species have been described on the basis of type materials from Australia that may fall within these three genera: Heterochaete cheesmanii Wakef. and Irpex depauperatus Massee.

Heterochaete cheesmanii was described by Wakefield (1915) from a collection on wood from New South Wales, characterized by the thin, orbicular basidiomes with a shortly reflexed margin, the pale hymenium with sparse, minute spines, the soft fulvous context, with 4-spored, cruciate basidia 15 × 10–12 μm, and curved, cylindrical spores, 14–15 × 5–5.5 μm, and hyphae 1.5–4 μm diameter. Reid (1957) examined the type at K and noted the presence of “conspicuous branched paraphyses”. Heterochaete cheesmanii differs from H. australiense by the shorter basidiospores. It will be necessary to obtain sequences from H. cheesmanii to ascertain its correct generic placement, but it could well be a member of Heteroradulum.

Irpex depauperatus was introduced by Massee (1901) with a short description, based on a collection on dead bark by Rodway from Tasmania. Note that due to existence of the previously described Irpex depauperatus Berk. & Broome, the replacement name Irpex tasmanicus Syd. & P. Syd. was introduced for I. depauperatus Massee. According to Massee (1901), Irpex depauperatus Massee was characterized by the tawny hymenium with short, laterally incised spines forming orbicular then confluent patches with a white edge and basidiospores of 6 × 3–4 μm. No comparison against other species was provided in the protologue. Both Bodman (1952) and Reid (1957) placed I. depauperatus as a synonym of other species. Without examining the type, Bodman (1952) listed I. depauperatus as a possible synonym of Heterochaete delicata (Klotzsch) Bres. However, Reid (1957) considered that I. depauperatus was a synonym of Eichleriella spinulosa (Berk. & M.A. Curtis) D.A. Reid (basionym Radulum spinulosum Berk. & M.A. Curtis, now accepted as Heteroradulum spinulosum). Reid (1957) provided a description of E. spinulosa (with I. depauperatus listed as synonym) that is evidently based on the cited Australian specimen (Miller s.n., K, Herb. F.P.S.M. No. 4996). Despite the fact that Massee (1901) originally described I. depauperatus as having basidiospores of 6 × 3–4 μm, Reid (1957) found that the type at K has basidiospores of 19 × 7 μm, matching the basidiospores from the Australian collection by Miller in 1954, but he did not provide any further details of the characters of the type collection of I. depauperatus.

Irpex depauperatus potentially belongs in Heteroradulum but due to slight morphological differences between species such as H. australiense and H. spinulosum, and the potential for further species to occur in the region, DNA sequences would be ideal to assist in interpretation of the old name. However, it is unlikely to be able to readily obtain DNA from the more than 100-year old type of Irpex depauperatus, which is borne out by unsuccessful attempts to amplify ITS and LSU sequences from several Australian collections in MEL filed under Heterochaete, collected in the 1950s and 1960s. Collections for which DNA amplification was unsuccessful included MEL 2313650 (which is a duplicate of the K collection Miller s.n., Herb. F.P.S.M. No. 4996). The morphology of Miller s.n. as recorded by Reid (1957) matches H. australiense in basidiospore size and shape and presence of skeletocystidia. However, the connection between this collection and the type of Irpex depauperatus is not definite, as only basidiospore dimensions of the latter were provided by Reid (1957). It remains possible that Irpex tasmanicus (= I. depauperatus) represents an earlier name for Heteroradulum australiense. Given the lack of a sequence from the type and the meagre morphological details available, we choose to introduce a new species, well-characterized by the combination of morphology and sequence data. Perhaps with the application of next generation sequencing, it may become possible to recover sequences from older types more routinely as has been done already in some cases, such as by Delgat et al. (2019).

Heteroradulum labyrinthinum (H.S. Yuan & C. Decock) L.W. Zhou, comb. nov.

MycoBank No: 842486

Basionym

Grammatus labyrinthinus H.S. Yuan & Decock, in Yuan, Lu & Decock, MycoKeys 35: 32 (2018)

Remarks

Heteroradulum labyrinthinum was placed in the new genus Grammatus as the generic type (Yuan et al. 2018). The main reason for introducing Grammatus was its irregularly irpicoid to poroid hymenophores, from a morphological perspective (Yuan et al. 2018). However, the morphological difference of hymenophores is not a reliable taxonomic character at the generic level within the Auriculariales. For example, Protomerulius Möller was recently shown to accommodate species with various kinds of hymenophore (Spirin et al. 2019a). This phenomenon also occurs in other groups of wood-inhabiting fungi (Wang et al. 2021). Moreover, taking the current phylogenetic evidence into consideration (Figure 1), we propose to treat Grammatus as a later synonym of Heteroradulum. Therefore, G. labyrinthinus is transferred to Heteroradulum, and Heteroradulum semis, that was moved to Grammatus (Yuan et al. 2018), is reaccepted as a member of Heteroradulum.

Species excluded from Heteroradulum

Heteroradulum yunnanense C.L. Zhao [as ‘ yunnanensis’], in Guan, Liu, Zhao & Zhao, Phytotaxa 437(2): 57 (2020)

Remarks

Heteroradulum yunnanense has a white to gray hymenophore and colorless hyphae (Guan et al. 2020), which do not fit well with the concept of Heteroradulum sensu Malysheva and Spirin (2017). According to the current phylogenetic evidence, we propose to exclude H. yunnanense from Heteroradulum.

A key to species of Heteroradulum

1 Hymenophore irpicoid to poroid H. labyrinthinum
Hymenophore grandinioid to odontioid 2
2 Hyphal system monomitic 3
Hyphal system dimitic 4
3 Basidiospores up to 14.2 μm long H. adnatum
Basidiospores up to 20.4 μm long H. deglubens
4 Basidiomes perennial H. kmetii
Basidiomes annual 5
5 Skeletocystidia present 6
Skeletocystidia absent 7
6 Generative hyphae septa with or without clamp connections H. australiense
Generative hyphae septa with clamp connections H. spinulosum
7 Cystidia absent H. brasiliense
Cystidia present 8
8 Basidiospores more than 15 μm long H. lividofuscum
Basidiospores less than 15 μm long H. semis

Discussion

In this study, the circumscription of Heteroradulum is emended by merging the genus Grammatus, adding the newly described species H. australiense and excluding the species H. yunnanense.

Recently, the concept of Protomerulius, another genus of the Auriculariales, was redefined to accommodate species bearing smooth, poroid and spiny hymenophores (Spirin et al. 2019a). The merging of Grammatus into Heteroradulum further indicates that while hymenophoral characters may be used to distinguish species they are not reliable characters at genera rank within the Auriculariales. In the case of the highly diverse macromorphological characters of species within the Auriculariales, the generic and, especially, familial delimitations should be cautiously explored with the aid of as comprehensive phylogenetic samplings as possible. Ideally, the construction of an order-level phylogenetic framework with wider taxon sampling and multimarker sequencing will help exactly clarify the higher-level relationships.

Heteroradulum yunnanense was placed in Heteroradulum based on a quite simple phylogeny with limited samples (Guan et al. 2020). Guan et al. (2020) stated that H. yunnanense grouped together with H. adnatum, but it actually was separated from all sampled species of Heteroradulum. The improper selection of outgroup taxa and absence of additional ingroup taxa lead to the inaccurate taxonomic placement of H. yunnanense. In the current phylogeny, H. yunnanense has a closer relationship with Exidiopsis calcea (Pers.) K. Wells, E. grisea (Bres.) Bourdot & Maire (TUFC100049) and an unnamed taxon of Exidiopsis (Figure 1). However, the generic type of Exidiopsis, E. effusa, is separated from the three so-called taxa of Exidiopsis. Consequently, it is premature to transfer H. yunnanense to another genus at this stage, but it clearly does not belong in Heteroradulum. A wider sampling of species related to H. yunnanense and disposition of species of Exidiopsis not conspecific with the type is needed to reveal its taxonomic position at a generic level.

Acknowledgements

The research was financed by the National Natural Science Foundation of China (Project Nos. 31970012 & 31770008).

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