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. 2023 Jan 10;12:1103579. doi: 10.3389/fcimb.2022.1103579

A phylogenetic and taxonomic study on Steccherinum (Polyporales, Basidiomycota): Focusing on three new Steccherinum species from southern China

Jun-Hong Dong 1,2, Xun-Chi Zhang 1,2, Jia-Jia Chen 3, Zhong-Long Zhu 4,*, Chang-Lin Zhao 1,2,5,*
PMCID: PMC9930103  PMID: 36817691

Abstract

The wood-inhabiting fungi play an integral role in wood degradation and the cycle of matter in the ecological system. They are considered as the “key player” in wood decomposition, because of their ability to produce all kinds of enzymes that break down woody lignin, cellulose and hemicellulose. In the present study, three new wood-inhabiting fungal species, Steccherinum fissurutum, S. punctatum and S. subtropicum spp. nov., collected from southern China, are proposed based on a combination of morphological features and molecular evidence. Steccherinum fissurutum is characterized by the resupinate, subceraceous basidiomata with cracked hymenophore, a monomitic hyphal system with clamped generative hyphae and cylindrical basidiospores; S. punctatum is characterized by the annual, punctate basidiomata with leathery hymenophore, cylindrical, strongly encrusted cystidia and ellipsoid basidiospores (3.6–4.5 ×2.6–3.4 µm); S. subtropicum is characterized by its effuse-reflexed basidiomata, a odontioid hymenophore with pink to lilac hymenial surface and ellipsoid basidiospores measuring as (2.8–3.4 × 2.0–2.7 µm). Sequences of ITS and nLSU rRNA markers of the studied samples were generated, and phylogenetic analyses were performed with maximum likelihood, maximum parsimony, and Bayesian inference methods. The ITS+nLSU analysis of the family Steccherinaceae indicated that the three new species clustered into the genus Steccherinum. Based on further analysis of ITS+nLSU dataset, the phylogenetic analysis confirmed that S. subtropicum was sister to S. enuispinum; S. fissurutum formed a monophyletic lineage; S. punctatum grouped with a clade comprised S. straminellum and S. ciliolatum.

Keywords: biodiversity, molecular systematics, Steccherinaceae, wood-inhabiting fungi, Yunnan Province

Introduction

The phylum Basidiomycota constitute a major group of the kingdom Fungi and is second in species numbers to the phylum Ascomycota (Wijayawardene et al., 2017; Wijayawardene et al., 2018a; Wijayawardene et al., 2018b). Wood-inhabiting fungal is a large group of Basidiomycota with simpler basidiomata with the diverse morphological features, but the phylogenetic diversity of this group is less intensively studied (Larsson et al., 2004; Bernicchia and Gorjón, 2010).

The genus Steccherinum Gray (Steccherinaceae, Polyporales), typified by S. ochraceum (Pers. ex J.F. Gmel.) Gray, was established by Gray (1821). It is a cosmopolitan genus characterized by a combination of resupinate to effused-reflexed or pileate basidiome with a membranaceous consistencey, hymenophore odontioid to hydnoid, a dimitic hyphal structure with clamp connections or simple-septate generative hyphae, cystidia numerous, strongly encrusted in the obtuse apex, basidia subclavate and basidiospores hyaline, thin-walled, smooth, ellipsoid to subcylindrical, acyanophilous and negative in Melzer’s reagent (Fries, 1821; Gray, 1821; Bernicchia and Gorjón, 2010). So far, about 80 species have been accepted in this genus worldwide (Fries, 1821; Banker, 1906; Banker, 1912; Cunningham, 1958; Snell and Dick, 1958; Lindsey and Gilbertson, 1977; Ryvarden, 1978; Lindsey and Gilbertson, 1979; Burdsall and Nakasone, 1981; Melo, 1995; Legon and Roberts, 2002; Yuan and Dai, 2005a; Spirin et al., 2007; Hjortstam and Ryvarden, 2008; Bernicchia and Gorjón, 2010; Miettinen et al., 2012; Yuan and Wu, 2012; Miettinen and Ryvarden, 2016; Westphalen et al., 2018; Liu and Dai, 2021; Westphalen et al., 2021; Wu et al., 2021a; Wu et al., 2021b; Dong et al., 2022). In recent years, several new Steccherinum species were described in China, S. fragile Z.B. Liu & Y.C. Dai, S. hirsutum Y.X. Wu & C.L. Zhao, S. puerense Y.X. Wu, J.H. Dong & C.L. Zhao, S. rubigimaculatum Y.X. Wu, J.H. Dong & C.L. Zhao, S. subcollabens (F. Wu, P. Du & X.M. Tian) Z.B. Liu & Y.C. Dai, S. tenuissimum C.L. Zhao & Y.X. Wu and S. xanthum C.L. Zhao & Y.X. Wu, and S. yunnanense Y.X. Wu & C.L. Zhao (Liu and Dai, 2021; Wu et al., 2021a; Wu et al., 2021b; Dong et al., 2022).

Molecular phylogenies have provided increased knowledge concerning the evolution of Steccherinum (Miettinen et al., 2012; Binder et al., 2013; Justo et al., 2017; Westphalen et al., 2018; Westphalen et al., 2021). Utilizing sequences of the gene regions ITS, nLSU, mtSSU, atp6, rpb2, and tef1, Miettinen et al. (2012) revealed that the phylogeny of the poroid and hydnoid genera Antrodiella Ryvarden and I. Johans., Junghuhnia Corda and Steccherinum (Polyporales, Basidiomycota) grouped together and Steccherinum was shown to contain both hydnoid and poroid species. Using of whole genome sequence data in comparison to extensively sampled multigene datasets indicated that Steccherinum species belonged to the residual polyporoid clade and the generic type (S. ochraceum) was grouped with Junghuhnia nitida (Pers.) Ryvarden (Binder et al., 2013). Justo et al. (2017) clarified family-level classification of eighteen families within the order Polyporales (Basidiomycota), which showed that Steccherinum belonged to family Steccherinaceae Parmasto. Westphalen et al. (2018) worked on morphological and multigene analyses of Junghuhnia s.lat., in which a new species Steccherinum neonitidum Westphalen & Tomšovský and three new combinations, S. meridionale (Rajchenb.) Westphalen, Tomšovský & Rajchenberg, S. polycystidiferum (Rick) Westphalen, Tomšovský & Rajchenb. and S. undigerum (Berk. & M.A. Curtis) Westphalen & Tomšovský were reported. Westphalen et al. (2021) provided the morphological and phylogenetic analyses on hydnoid specimens of Steccherinaceae, in which four genera as Cabalodontia Piatek, Etheirodon Banker, Metuloidea G. Cunn., and Steccherinum were introduced and three new neotropical species was found.

Scientific names are important link to communicate biological information across many spheres of use, in which how to publish a new fungal species is recommended to provide DNA barcode sequences in a public repository for the holotype specimen with the barcode locus (ITS) as well as any additional taxa specific secondary barcode loci (Aime et al., 2021). In order to allow BLAST searches to work optimally, sequences of DNA barcodes should include the generally used region for that marker (Aime et al., 2021). Sometimes, this genus Steccherinum for the barcoding gene ITS is less than 97% of nucleotide difference between different species.

The aim of this study is to explore the diversity and phylogeny of Steccherinum in China. During our investigations on the diversity of wood-inhabiting fungi in southern China, three undescribed species were collected from Yunnan Province, and their morphology corresponds to the concept of Steccherinum. To confirm their placement in Steccherinum, morphological examination and phylogenetic analyses based on the internal transcribed spacer (ITS) and large subunit nuclear ribosomal RNA (nLSU) genens, were carried out.

Materials and methods

Morphological studies

The studied specimens are deposited at the herbarium of Southwest Forestry University (SWFC), Yunnan Province, P.R. China (Herbarium numbers: Steccherinum fissurutum: SWFCF00021634, SWFCF00021673, SWFCF00021675, SWFCF00021680, SWFCF00021703, SWFCF00021744, SWFCF00021754, SWFCF00020803, SWFCF00021808, SWFCF00021811, SWFCF00021826, SWFCF00021841; S. punctatum: SWFCF00009181, SWFCF00009184; S. subtropicum: SWFCF00011059, SWFCF00016901). Macromorphological descriptions are based on field notes. Petersen (1996) was followed for the colour terms. Micromorphological data were obtained from the dried specimens and observed under a light microscope Eclipse E 80i (Nikon, Tokyo) following Dai (2012). The following abbreviations were used for the micro characteristics description: KOH = 5% potassium hydroxide, CB = Cotton Blue, CB– = acyanophilous, IKI = Melzer’s reagent, IKI– = both non-amyloid and non-dextrinoid, L = mean spore length (arithmetic average of all spores), W = mean spore width (arithmetic average of all spores), Q = variation in the L/W ratios between the specimens studied, n (a/b) = number of spores (a) measured from given number (b) of specimens.

Molecular procedures and phylogenetic analyses

CTAB rapid plant genome extraction kit-DN14 (Aidlab Biotechnologies Co., Ltd, Beijing) was used to obtain genomic DNA from dried specimens, according to the manufacturer’s instructions. ITS region was amplified with primer pairs ITS5 and ITS4 (White et al., 1990). Nuclear LSU region was amplified with primer pairs LR0R and LR7 (https://sites.duke.edu/vilgalyslab/rdna_primers_for_fungi/ ) Table 1 .

Table 1.

A list of genes, primers and primer sequences used in this study.

Fragment of amplification Name of primer Primer base sequence (5′-3′) b References
ITS ITS5 GGA AGT AAA AGT CGT AAC AAG G White et al., 1990
ITS4 TCC TCC GCT TAT TGA TAT GC
nLSU LR0R ACC CGC TGA ACT TAA GC http://www.biology.duke.edu/fungi/mycolab/primers.htm
LR7 TAC TAC CAC CAA GAT CT
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b

degenerate base: R = A or G, Y = C or T, N = A or T or C or G, V = G or A.

The PCR procedure for ITS was as follows: initial denaturation at 95°C for 3 min, followed by 35 cycles at 94°C for 40 s, 58°C for 45 s and 72°C for 1 min, and a final extension of 72°C for 10 min. The PCR procedure for nLSU was as follows: initial denaturation at 94°C for 1 min, followed by 35 cycles at 94°C for 30 s, 48°C 1 min and 72°C for 1.5 min, and a final extension of 72°C for 10 min. The PCR products were purified and sequenced at Kunming Tsingke Biological Technology Limited Company, Kunming, Yunnan Province, P.R. China. All newly generated sequences were deposited at GenBank ( Table 2 ).

Table 2.

List of species, specimens and GenBank accession numbers of sequences used in this study. * is shown type material, holotype.

Species Name Sample No. GenBank Accession No. References
ITS nLSU
Antella americana KHL 11949 JN710509 JN710509 Cao et al., 2021
A. americana HHB-4100 KP135316 KP135196 Cao et al., 2021
A. chinensis Dai 8874 JX110843 KC485541 Yuan, 2013
A. chinensis Dai 9019 JX110844 KC485542 Yuan, 2013
A. niemelaei Renvall 3218 AF126876 — Cao et al., 2021
A. niemelaei Haikonen 14727 AF126877 — Cao et al., 2021
Antrodiella onychoides Miettinen 2312 JN710517 JN710517 Miettinen et al., 2012
A. pallescens Nordén 8.8.2008 JN710518 JN710518 Miettinen et al., 2012
A. romellii Miettinen 7429 JN710520 JN710520 Miettinen et al., 2012
A. semisupina Labrecque & Labbé 372 JN710521 JN710521 Miettinen et al., 2012
A. stipitata FD-136 KP135314 KP135197 Westphalen et al., 2021
A. stipitata Yuan 5640 KC485525 KC485544 Yuan, 2014
Atraporiella neotropica Miettinen X1021 HQ659221 HQ659221 Cao et al., 2021
A. yunnanensis CLZhao 604 MF962482 MF962485 Wu et al., 2017
A. yunnanensis CLZhao 605 MF962483 MF962486 Wu et al., 2017
Butyrea japonica MN 1065 JN710556 JN710556 Cao et al., 2021
B. luteoalba FP-105786 KP135320 KP135226 Dong et al., 2022
B. luteoalba KHL 13238b JN710558 JN710558 Dong et al., 2022
Climacocystis borealis KHL 13318 JN710527 JN710527 Cao et al., 2021
Elaphroporia ailaoshanensis CLZhao 596 MG231572 MG748855 Wu et al., 2018
E. ailaoshanensis CLZhao 597 MG231847 MG748856 Wu et al., 2018
Etheirodon fimbriatum KHL 11905 JN710530 JN710530 Cao et al., 2021
E. fimbriatum HR 98811 MT849300 — Westphalen et al., 2021
E. purpureum MCW 642/18 MT849301 MT849301 Westphalen et al., 2021
Flaviporus brownii MCW 362/12 KY175008 KY175008 Westphalen et al., 2018
F. brownie X 462 JN710538 JN710538 Cao et al., 2021
F. liebmannii X 249 JN710539 JN710539 Cao et al., 2021
F. liebmannii Yuan 1766 KC502914 — Yuan, 2014
F. subundatus MCW 367/12 KY175004 KY175004 Westphalen et al., 2018
F. subundatus MCW 457/13 KY175005 KY175005 Westphalen et al., 2018
F. tenuis MCW 442/13 KY175001 KY175001 Westphalen et al., 2018
F. tenuis MCW 356/12 KY175002 KY175002 Westphalen et al., 2018
Frantisekia fissiliformis CBS 435.72 MH860521 MH872232 Vu et al., 2019
F. mentschulensis BRNM 710170 FJ496670 FJ496728 Dong et al., 2022
F. mentschulensis AH 1377 JN710544 JN710544 Dong et al., 2022
F. ussurii Wei 3081 KC485527 KC485545 Yuan, 2014
F. ussurii Dai 8249 KC485526 — Yuan, 2014
Irpex lacteus DO 421/951208 JX109852 JX109852 Dong et al., 2022
Junghuhnia crustacea X 262 JN710553 JN710553 Miettinen et al., 2012
J. delicate MCW 564/17 MT849295 MT849295 Du et al., 2020
J. delicate MCW 693/19 MT849297 MT849297 Du et al., 2020
J. pseudocrustacea Yuan 6160 MF139551 — Yuan et al., 2019
J. pseudocrustacea Zhou 283 MF139552 — Yuan et al., 2019
Loweomyces fractipes X 1149 JN710570 JN710570 Cao et al., 2021
L. fractipes MT 13/2012 KX378866 KX378866 Cao et al., 2021
L. spissus MCW 488/14 KX378869 KX378869 Cao et al., 2021
L. tomentosus MCW 366/12 KX378870 KX378870 Cao et al., 2021
L. wynneae X 1215 JN710604 JN710604 Cao et al., 2021
Metuloidea cinnamomea X 1228 KU926963 — Cao et al., 2021
M. fragrans LE 295277 KC858281 — Cao et al., 2021
M. murashkinskyi X 449 JN710588 JN710588 Cao et al., 2021
M. reniformis MCW 542/17 MT849303 MT849303 Westphalen et al., 2021
M. reniformis MCW 523/17 MT849302 MT849302 Westphalen et al., 2021
M. rhinocephala X 460 JN710562 JN710562 Cao et al., 2021
Mycorrhaphium hispidum MCW 363/12 MH475306 MH475306 Cao et al., 2021
M. hispidum MCW 429/13 MH475307 MH475307 Cao et al., 2021
M. subadustum Yuan 12976 MW491378 MW488040 Cao et al., 2021
M. subadustum Dai 10173 KC485537 KC485554 Cao et al., 2021
Nigroporus stipitatus KaiR 116 MT110231 MT110231 Piepenbring et al., 2020
N. vinosus MQN 015 AB811861 AB811861 Hai Bang et al., 2014
N. vinosus X 839 JN710575 JN710575 Cao et al., 2021
Steccherinum autumnale Spirin 2957 JN710549 JN710549 Liu and Dai, 2021
S. bourdotii HR99893 MT849311 Westphalen et al., 2021
S. bourdotii Saarenoksa 10195 JN710584 JN710584 Miettinen et al., 2012
S. ciliolatum Ryvarden 47033 JN710585 JN710585 Miettinen et al., 2012
S. collabens KHL 11848 JN710552 JN710552 Liu and Dai, 2021
S. fissurutum CLZhao 21803 * OP799385 OP799397 Present study
S. fissurutum CLZhao 21841 OP799388 OP799400 Present study
S. fissurutum CLZhao 21808 OP799386 OP799398 Present study
S. fissurutum CLZhao 21675 OP799380 OP799392 Present study
S. fissurutum CLZhao 21811 OP799389 OP799399 Present study
S. fissurutum CLZhao 21680 OP799381 OP799393 Present study
S. fissurutum CLZhao 21703 OP799382 OP799394 Present study
S. fissurutum CLZhao 21744 OP799383 OP799395 Present study
S. fissurutum CLZhao 21826 OP799387 — Present study
S. fissurutum CLZhao 21634 OP799378 — Present study
S. fissurutum CLZhao 21673 OP799379 — Present study
S. fissurutum CLZhao 21754 OP799384 OP799396 Present study
S. fragile Dai 19972 MW364629 MW364627 Liu and Dai, 2021
S. fragile Dai 20479 MW364628 MW364626 Liu and Dai, 2021
S. hirsutum CLZhao 4222 MW290040 MW290054 Dong et al., 2022
S. hirsutum CLZhao 4523 MW290041 MW290055 Dong et al., 2022
S. larssonii MCW 593/17 MT849306 MT849306 Westphalen et al., 2021
S. larssonii MCW 594/17 MT849307 MT849307 Westphalen et al., 2021
S. meridionalis MR 10466 KY174994 KY174994 Westphalen et al., 2018
S. meridionalis MR 284 KY174992 KY174992 Westphalen et al., 2018
S. neonitidum MCW 371/12 KY174990 KY174990 Westphalen et al., 2018
S. neonitidum RP 79 KY174991 KY174991 Westphalen et al., 2018
S. nitidum KHL 11903 JN710560 JN710560 Westphalen et al., 2018
S. nitidum MT 33/12 KY174989 KY174989 Westphalen et al., 2018
S. ochraceum KHL11902 JN710590 JN710590 Westphalen et al., 2021
S. ochraceum 2060 JN710589 JN710589 Liu and Dai, 2021
S. polycystidiferum RP 140 KY174996 KY174996 Westphalen et al., 2018
S. polycystidiferum MCW 419/12 KY174995 KY174995 Westphalen et al., 2018
S. pseudozilingianum Kulju 1004 JN710561 JN710561 Liu and Dai, 2021
S. puerense CLZhao 3122 MW682341 — Wu et al., 2021a
S. puerense CLZhao 3644 MW682342 MW682338 Wu et al., 2021a
S. punctatum CLZhao 9181 OP799375 OP799401 Present study
S. punctatum CLZhao 9184 * OP799376 OP799402 Present study
S. robustius G1195 JN710591 JN710591 Cao et al., 2021
S. rubigimaculatum CLZhao 4069 MW682343 MW682339 Wu et al., 2021a
S. rubigimaculatum CLZhao 10638 MW682344 MW682340 Wu et al., 2021a
S. straminellum KHL 13849 JN710597 JN710597 Cao et al., 2021
S. subcollabens Dai 19344 MN871758 MN877771 Liu and Dai, 2021
S. subcollabens Dai 19345 MN871759 MN877772 Liu and Dai, 2021
S. subtropicum CLZhao 16901 OP799391 — Present study
S. subtropicum CLZhao 11059 * OP799390 OP799377 Present study
S. tenue FP-102082 KY948817 — Liu and Dai, 2021
S. tenue KHL 12316 JN710598 JN710598 Liu and Dai, 2021
S. tenuispinum Spirin 2116 JN710600 JN710600 Miettinen et al., 2012
S. tenuispinum Miettinen 8065 JN710599 JN710599 Miettinen et al., 2012
S. undigerum MCW 472/13 KY174987 KY174987 Westphalen et al., 2018
S. undigerum MCW 426/13 KY174986 KY174986 Westphalen et al., 2018
S. xanthum CLZhao 5030 MW204588 MW204577 Wu et al., 2021b
S. xanthum CLZhao 5032 MW204589 MW204578 Wu et al., 2021b
S. yunnanense CLZhao 1445 MW290042 MW290056 Dong et al., 2022
S. yunnanense CLZhao 2822 MW290043 MW290057 Dong et al., 2022
Trullella conifericola Cui 2851 MT269764 — Cao et al., 2021
T. conifericola Yuan 12655 MT269760 MT259326 Cao et al., 2021
T. dentipora X 200 JN710512 JN710512 Cao et al., 2021
T. duracina MCW 410/13 MH475309 MH475309 Cao et al., 2021
T. duracina RP 96 MH475310 MH475310 Cao et al., 2021
Xanthoporus syringae Jeppson 2264 JN710607 JN710607 Cao et al., 2021
X. syringae AFTOL-ID 774 AY789078 AY684166 Cao et al., 2021
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* is shown type material, holotype.

The sequences were aligned in MAFFT version 7 (Katoh et al., 2019) using the G-INS-i strategy. The alignment was adjusted manually using AliView version 1.27 (Larsson, 2014). The dataset was aligned first and then ITS and nLSU sequences were combined with Mesquite version 3.51. Alignment datasets were deposited in TreeBASE (submission ID 29889). Sequence of Climacocystis borealis (Fr.) Kotl. & Pouzar obtained from GenBank was used as an outgroup to root trees in the ITS+nLSU analysis in the family Steccherinaceae ( Figure 1 ), and Irpex lacteus (Fr.) Fr. was used as an outgroup in the ITS+nLSU analysis in the genus Steccherinum ( Figure 2 ) (Dong et al., 2022).

Figure 1.

Figure 1

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Maximum parsimony strict consensus tree illustrating the phylogeny of three new species and related species in the family Steccherinaceae based on ITS+nLSU sequences. Branches are labeled with maximum likelihood bootstrap values higher than 70%, parsimony bootstrap values higher than 50% and Bayesian posterior probabilities more than 0.95 respectively.

Figure 2.

Figure 2

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Maximum parsimony strict consensus tree illustrating the phylogeny of three new species and related species in Steccherinum based on ITS+nLSU sequences. Branches are labeled with maximum likelihood bootstrap values higher than 70%, parsimony bootstrap values higher than 50% and Bayesian posterior probabilities more than 0.95 respectively.

Maximum parsimony (MP), maximum likelihood (ML) and Bayesian inference (BI) analyses were applied to the combined three datasets following previous study (Zhao and Wu, 2017), and the tree construction procedure was performed in PAUP* version 4.0b10 (Swofford, 2002). All characters were equally weighted and gaps were treated as missing data. Trees were inferred using the heuristic search option with TBR branch swapping and 1000 random sequence additions. Max-trees were set to 5000, branches of zero length were collapsed, and all parsimonious trees were saved. Clade robustness was assessed using bootstrap (BT) analysis with 1000 replicates (Felsenstein, 1985). Descriptive tree statistics-tree length (TL), consistency index (CI), retention index (RI), rescaled consistency index (RC), and homoplasy index (HI) were calculated for each maximum parsimonious tree generated. The multiple sequence alignment was also analyzed using maximum likelihood (ML) in RAxML-HPC2 through the Cipres Science Gateway (Miller et al., 2012). Branch support (BS) for ML analysis was determined by 1000 bootstrap replicates.

MrModeltest 2.3 (Nylander, 2004) was used to determine the best-fit evolution model for each data set for Bayesian inference (BI), which was performed using MrBayes 3.2.7a with a GTR+I+G model of DNA substitution and a gamma distribution rate variation across sites (Ronquist et al., 2012). A total of 4 Markov chains were run for 2 runs from random starting trees for 2.8 million generations for ITS+nLSU in Steccherinaceae ( Figure 1 ), and 1.7 million generations for ITS+nLSU in Steccherinum ( Figure 2 ) with trees and parameters sampled every 1000 generations. The first one-fourth of all generations was discarded as burn-in. The majority rule consensus tree of all remaining trees was calculated. Branches were considered as significantly supported if they received maximum likelihood bootstrap value (BS) >70%, maximum parsimony bootstrap value (BT) >70%, or Bayesian posterior probabilities (BPP) >0.95.

Results

Molecular phylogeny

The ITS+nLSU dataset ( Figure 1 ) included sequences from 82 fungal specimens representing 50 species. The dataset had an aligned length of 2257 characters, of which 1304 characters are constant, 237 are variable and parsimony uninformative, and 716 are parsimony informative. Maximum parsimony analysis yielded 36 equally parsimonious trees (TL = 3992, CI = 0.3885, HI = 0.6115, RI = 0.6621, and RC = 0.2572). The best model for the ITS+nLSU dataset estimated and applied in the Bayesian analysis was GTR+I+G (lset nst = 6, rates = invgamma; prset statefreqpr = dirichlet (1,1,1,1)). Bayesian analysis and ML analysis resulted in a similar topology to MP analysis with an average standard deviation of split frequencies = 0.007830 (BI), and the effective sample size (ESS) across the two runs is the double of the average ESS (avg ESS) = 182.

The phylogram inferred from the ITS+nLSU rDNA gene regions ( Figure 1 ) showed that sixteen genera nested into the family Steccherinaceae as Antella Miettinen, Antrodiella Ryvarden & I.johans, Atraporiella Ryvarden, Butyrea Miettinen, Elaphroporia Z.Q. Wu & C.L. Zhao, Etheirodon Banker, Flaviporus Murrill, Frantisekia Spirin & Zmitr, Junghuhnia Corda, Loweomyces (Kotl. & Pouzar) Jülich, Metuloidea G. Cunn, Mycorrhaphium Maas Geest, Nigroporus Murrill, Steccherinum, Trullella Zmitr and Xanthoporus Audet, in which three new species Steccherinum fissurutum, S. punctatum and S. subtropicum grouped into genus Steccherinum.

The ITS+nLSU dataset ( Figure 2 ) included sequences from 57 fungal specimens representing 27 species. The dataset had an aligned length of 2068 characters, of which 1465 characters are constant, 168 are variable and parsimony-uninformative, and 435 are parsimony-informative. Maximum parsimony analysis yielded 5000 equally parsimonious trees (TL = 1640, CI = 0.5213, HI = 0.4787, RI = 0.7996, RC = 0.4169). Best model for the ITS+nLSU dataset estimated and applied in the Bayesian analysis was GTR+I+G (lset nst = 6, rates = invgamma; prset statefreqpr = dirichlet (1,1,1,1). Bayesian analysis and ML analysis resulted in a similar topology to MP analysis with an average standard deviation of split frequencies = 0.009192 (BI), and the effective sample size (ESS) across the two runs is the double of the average ESS (avg ESS) = 198.

The phylogenetic tree ( Figure 2 ) inferred from ITS+nLSU sequences covered 26 species of Steccherinum, which demonstrated that S. subtropicum was sister to S. enuispinum; S. fissurutum formed a monophyletic lineage; S. punctatum grouped with a clade comprised S. straminellum (Bres.) Melo and S. ciliolatum (Berk. & M.A. Curtis) Gilb. & Budington.

Taxonomy

Steccherinum fissurutum J.H. Dong & C.L. Zhao, sp. nov. Figures 3 , 4 .

Figure 3.

Figure 3

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Basidiomata of Steccherinum fissurutum (holotype). Bars: (A) 1 cm; (B) 0.5 mm.

Figure 4.

Figure 4

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Microscopic structures of Steccherinum fissurutum (drawn from the holotype). (A) Basidiospores. (B) Basidia and basidioles. (C) Skeletocystidia. (D) A section of hymenium. Bars: (A) 5 µm; (B–D) 10 µm.

Hierarchical information: Fungi, Dikarya, Basidiomycota, Agaricomycotina, Agaricomycetes, Polyporales, Steccherinaceae, Steccherinum.

MycoBank no.: MB 846499.

Diagnosis: differs from other Steccherinum species by its white to buff, cracked, subceraceous, grandinoid hymenial surface, a monomitic hyphal system with clamped generative hyphae and cylindrical basidiospores measuring 4.5–6.0 × 2.5–3.0 µm.

Holotype—China. Yunnan Province, Lijiang, Heilongtan Park, Xiangshan, GPS coordinates 26°53′ N, 100°13′ E, altitude 2, 400 m asl., on the fallen branch of angiosperm, leg. C.L. Zhao, 21 July 2021, CLZhao 21803 (SWFC).

Etymology—fissurutum (Lat.): referring to the cracked hymenophore surface of the type specimens.

Basidiomata: Annual, resupinate, adnate, cracked, subceraceous, without odor or taste when fresh, becoming brittle upon drying, up to 10 cm long, up to 2 cm wide, 50–150 µm thick. Hymenial surface grandinoid, aculei 3–5 per mm, the length of aculei up to 0.2 mm, white (60) when fresh, turning to white (60) to buff (13) upon drying. Sterile margin white, 0.5 mm wide.

Hyphal system: Monomitic, generative hyphae with clamp connections, colorless, thin-walled, frequently branched, interwoven, 2.5–3.5 µm in diam. IKI–, CB–, tissues unchanged in KOH.

Hymenium: Skeletocystidia numerous in the aculei, strongly encrusted in the obtuse apex, 26.5–36 × 6.5–9.5 µm; cystidioles absent. Basidia clavate, with 4 sterigmata and a basal clamp connection, 12.5–16.5 × 4.5–7 µm; basidioles dominant, in shape similar to basidia, but slightly smaller.

Basidiospores: Cylindrical, colorless, thin-walled, with one oil drop inside, IKI–, CB–, 4.5–6.0 × 2.5–3.0 µm, L = 5.23 µm, W = 2.79 µm, Q = 1.75–1.98 (n = 180/6).

Type of rot: White rot.

Additional specimens examined (paratypes): CHINA, Yunnan Province, Lijiang, Heilongtan Park, Xiangshan, GPS coordinates 26°53′ N, 100°13′ E, altitude 2, 400 m asl., on the fallen branch of angiosperm, leg. C.L. Zhao, 21 July 2021, CLZhao 21634, 21673, 21675, 21680, 21703, 21744, 21754, 21808, 21811, 21826, 21841 (SWFC).

Steccherinum punctatum J.H. Dong & C.L. Zhao, sp. nov. Figures 5 , 6 .

Figure 5.

Figure 5

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Basidiomata of Steccherinum punctatum (holotype). Bars: (A) 1 cm; (B) 0.5 mm.

Figure 6.

Figure 6

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Microscopic structures of Steccherinum punctatum (drawn from the holotype). (A) Basidiospores. (B) Basidia and basidioles. (C) Skeletocystidia. (D) A section of hymenium. Bars: (A) 5 µm; (B–D) 10 µm.

Hierarchical information: Fungi, Dikarya, Basidiomycota, Agaricomycotina, Agaricomycetes, Polyporales, Steccherinaceae, Steccherinum.

MycoBank no.: MB 846500.

Diagnosis: differs from other Steccherinum species by its cream to buff, punctate, grandinoid hymenial surface, a monomitic hyphal system with clamped generative hyphae and ellipsoid basidiospores measuring 3.6–4.5 × 2.6–3.4 µm.

Holotype—China. Yunnan Province, Yuxi, Xinping County, Jinshan Primeval Forest Park, GPS coordinates 24°07′ N, 101°99′ E, altitude 2, 300 m asl., on the stump of angiosperm, leg. C.L. Zhao, 2 January 2019, CLZhao 9184 (SWFC).

Etymology—punctatum (Lat.): referring to the punctate hymenophore surface.

Basidiomata: Annual, resupinate, adnate, punctate, soft leathery, without odor or taste when fresh, becoming leathery upon drying, up to 15 cm long, up to 5 cm wide, 50–100 µm thick. Hymenial surface grandinoid, aculei 5–9 per mm, the length of aculei up to 0.1 mm, white (60) when fresh, turning to cream (21) to buff (13) upon drying. Sterile margin cream, 0.5 mm wide.

Hyphal system: Monomitic, generative hyphae with clamp connections, colorless, thin-walled, frequently branched, interwoven, 3–4.5 µm in diam. IKI–, CB–, tissues unchanged in KOH.

Hymenium: Skeletocystidia numerous, thin-walled, cylindrical, strongly encrusted in the surface and almost entirely, 36–47 × 7.5–12 µm; cystidioles absent. Basidia subclavate to barrel, with 4 sterigmata and a basal clamp connection, 23–27 × 5.5–7.5 µm; basidioles dominant, in shape similar to basidia, but slightly smaller.

Basidiospores: Ellipsoid, colorless, thin-walled, smooth, with one oil drop inside, IKI–, CB–, 3.6–4.5(–4.7) × 2.6–3.4 µm, L = 4.00 µm, W = 2.88 µm, Q = 1.37–1.42 (n = 60/2).

Type of rot: White rot.

Additional specimen examined (paratype): CHINA, Yunnan Province, Yuxi, Xinping County, Jinshan Primeval Forest Park, GPS coordinates 24°07′ N, 101°99′ E, altitude 2, 300 m asl., on the stump of angiosperm, leg. C.L. Zhao, 2 January 2019, CLZhao 9181 (SWFC).

Steccherinum subtropicum J.H. Dong & C.L. Zhao, sp. nov. Figures 7 , 8 .

Figure 7.

Figure 7

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Basidiomata of Steccherinum subtropicum (holotype). Bars: (A) 1 cm; (B) 0.5 mm.

Figure 8.

Figure 8

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Microscopic structures of Steccherinum subtropicum (drawn from the holotype). (A) Basidiospores. (B) Skeletocystidia. (C) Basidia and basidioles. (D) A section of hymenium. Bars: (A) 5 µm; (–D) 10 µm.

Hierarchical information: Fungi, Dikarya, Basidiomycota, Agaricomycotina, Agaricomycetes, Polyporales, Steccherinaceae, Steccherinum.

MycoBank no.: MB 846501.

Diagnosis: differs from other Steccherinum species by its pink to lilac, effuse-reflexed, odontioid hymenial surface, a dimitic hyphal system with clamped generative hyphae and ellipsoid basidiospores measuring 2.8–3.4 × 2.0–2.7 µm.

Holotype—China. Yunnan Province, Wenshan, Xichou County, Xiaoqiaogou National Nature Reserve, GPS coordinates 23°22′ N, 104°47′ E, altitude 1700 m asl., on the fallen branch of angiosperm, leg. C.L. Zhao, 15 January 2019, CLZhao 11059 (SWFC).

Etymology—subtropicum (Lat.): referring to distribution (subtropical zone) of the type specimens.

Basidiomata: Annual, effuse-reflexed, without odor or taste when fresh, becoming leathery upon drying, up to 6 cm long, up to 1.5 cm wide, 100–150 µm thick. Hymenial surface odontioid, aculei 5–7 per mm, the length of aculei 0.5–1 mm long, fresh pink (27) when fresh, turning to rose (28) to lilac (48) upon drying. Sterile margin cream, 0.5–1 mm wide.

Hyphal system: Dimitic, generative hyphae with clamp connections, colorless, thin-walled, branched, more or less interwoven, 2.3–3.5 µm in diam. Skeletal hyphae colorless, thick-walled, 3.5–4.5 µm diam; all hyphae IKI–, CB–, tissues unchanged in KOH.

Hymenium: Skeletocystidia numerous strongly encrusted in the obtuse apex, 20–82 × 5.5–10 µm; cystidioles absent. Basidia clavate, with 4 sterigmata and a basal clamp connection, 14.5–20 × 4–6 µm; basidioles dominant, in shape similar to basidia, but slightly smaller.

Basidiospores: Ellipsoid, colorless, thin-walled, IKI–, CB–, 2.8–3.4 × 2.0–2.7 µm, L = 3.00 µm, W = 2.31 µm, Q = 1.24–1.37 (n = 60/2).

Type of rot: White rot.

Additional specimen examined (paratype): CHINA, Yunnan Province, Wenshan, Xiaojie Town, Laojunshan National Nature Reserve, GPS coordinates 22°56′ N, 104°37′ E, altitude 2500 m asl., on the fallen branch of angiosperm, leg. C.L. Zhao, 15 January 2019, CLZhao 16901 (SWFC).

Discussion

In the present study, three new species, Steccherinum fissurutum, S. punctatum and S. subtropicum are described based on phylogenetic analyses and morphological characters.

Phylogenetically, seven clades were found in Polyporales: the residual polyporoid clade, the phlebioid clade, the antrodia clade, the tyromyces clade, the fragiliporia clade, the core polyporoid clade and the gelatoporia clade (Binder et al., 2005; Binder et al., 2013). Miettinen et al. (2012) employed the molecular systematics of Steccherinum and related genera Antrodiella, and Junghuhnia utilizing sequences of the gene regions ITS, nLSU, mtSSU, ATPase subunit 6 (atp6), RNA polymerase II second largest subunit (rpb2), and translation elongation factor 1-alpha (tef1), to reveal that at least 16 transitions have taken place between poroid and hydnoid hymenophore types within the family Steccherinaceae. In the present study, based on the sequences of the gene regions ITS and nLSU ( Figure 1 ), three new species, S. fissurutum, S. punctatum and S. subtropicum nested within the genus Steccherinum. Amplifying ITS and nLSU genes across genus Steccherinum ( Figure 2 ), S. fissurutum formed a monophyletic lineage; S. punctatum grouped with a clade comprised S. straminellum and S. ciliolatum; S. subtropicum was sister to S. tenuispinum Spirin, Zmitr. & Malysheva. However, morphologically, S. straminellum differs from S. punctatum by having the dimitic hyphal system and narrower basidiospores (3.5–4.5 × 2.0–2.2 µm; Melo, 1995); S. ciliolatum is distinguished from S. punctatum by having narrowly ellipsoid to cylindrical basidiospores (4–4.5 × 2.2–2.5 µm; Maas Geesteranus, 1974). S. tenuispinum differs from S. subtropicum by its fimbriate rhizomorphs and longer aculei (1–4 mm; Spirin et al., 2007).

Morphologically, Steccherinum fissurutum resembles S. litschaueri and S. ciliolatum in having cylindrical basidiospores. However, S. litschaueri is distinguished from S. fissurutum by its rhizomorphic margin and narrower basidiospores (4.5–5.5 × 2.0–2.2 µm; Bernicchia and Gorjón, 2010). Steccherinum ciliolatum differs in having longer aculei (up to 1.5 mm) and longer basidia (18–22 × 4.5–6 µm; Maas Geesteranus, 1974).

Steccherinum punctatum is similar to S. hydneum Rick ex Maas Geest., S. tenuispinum and S. yunnanense in having leathery hymenophore. However, S. hydneum differs from S. punctatum by its longer aculei (2–3 mm) and wider basidiospores (4.2–5.0 × 3.6–4.1 µm; Yuan and Dai, 2005b); S. tenuispinum differs from S. punctatum in having whitish to dirty-ochraceous hymenial surface and narrower basidia (12–24 × 3.5–4.8 µm; Spirin et al., 2007); S. yunnanense differs in its fimbriate margin and shorter basidia (10.5–15 × 5–6 µm; Dong et al., 2022). Steccherinum punctatum resembles S. aggregatum Hjortstam & Spooner, S. fragile and S. xanthum in having a monomitic hyphal system. However, S. aggregatum is distinguished from S. punctatum by having longer cystidia (100–150 × 10–12 µm) and smaller basidia (15–20 × 4–5 µm; Hjortstam et al., 1990); S. fragile differs in having the fragile basidiomata and smaller basidiospores (2.8–3.1 × 2.1–2.2 μm; Liu and Dai, 2021). Steccherinum xanthum is distinguished from S. punctatum in having smaller basidia (10–19.3 × 3–5.2 μm; Wu et al., 2021b).

Steccherinum subtropicum is similar to S. hydneum, S. oreophilum Lindsey & Gilb. and S. rubigimaculatum in the effuse-reflexed basidiomata. However, S. hydneum differs from S. subtropicum by its cinnamon buff hymenial surface and larger basidiospores (4.2–5.0 × 3.6–4.1 µm; Yuan and Dai, 2005b). Steccherinum oreophilum differs in its cottony hymenophore and larger basidiospores (5–6.5 × 3–3.2 µm; Bernicchia and Gorjón, 2010); S. rubigimaculatum differs in having rust hymenial surface and longer basidiospores (3.5–5 × 2.5–3.5 µm; Wu et al., 2021a); S. subtropicum resembles S. fragile, S. ochraceum and S. robustius (J. Erikss. & S. Lundell) J. Erikss. in having ellipsoid basidiospores. However, S. fragile is distinguished from S. subtropicum in having a monomitic hyphal system and shorter basidia (13–14 × 4.0–4.5 µm; Liu and Dai, 2021). S. ochraceum differs in its ocherous hymenial surface and longer cystidia (100 × 7–10 µm; Bernicchia and Gorjón, 2010). The species S. robustius is distinguished from S. subtropicum by its fimbriate margin and longer basidiospores (3.5–5 × 2.5–3 µm; Bernicchia and Gorjón, 2010).

Fungi are one of the most diverse groups of organisms on Earth and play a crucial role in ecosystem processes and functions (Hyde, 2022). New DNA sequencing techniques have revolutionized the researches of fungal taxonomy and diversity, in which about 150 thousand species of fungi have been described (Hyde, 2022). Wood decaying fungi have been studied intensively in recent years (Bernicchia and Gorjón, 2010; Dai, 2011; Cui et al., 2019; Guan et al., 2020; Wang and Zhao, 2021; Westphalen et al., 2021; Wu et al., 2021a; Wu et al., 2021b; Wu et al., 2021b; Luo and Zhao, 2022; Luo et al., 2022; Qu et al., 2022; Wu et al., 2022a; Wu et al., 2022b), but the hydnoid species in the order Polyporales are still not well investigated in China, especially in the subtropics and tropics. In the present study, three new species, Steccherinum fissurutum, S. punctatum and S. subtropicum spp. nov. were found in subtropics, which enriches the fungal diversity of East Asia.

Key to species of Steccherinum sensu lato from China

1. Hyphal system monomitic in subiculum······························2

1. Hyphal system dimitic in subiculum····································8

2. Basidiospores <2 μm wide··········Mycorrhaphium adustum

2. Basidiospores >2 μm wide······················································3

3. Skeletocystidia absent····························Steccherinum fragile

3. Skeletocystidia present·····························································4

4. Aculei >1mm long·············································S. aggregatum

4. Aculei <1 mm long···································································5

5. Aculei <0.3 mm long, basidiospores with oil drops··········6

5. Aculei >0.3 mm long, basidiospores without oil drops···································································Cabalodontia queletii

6. Basidia >20 μm long··········································S. punctatum

6. Basidia <20 μm long································································7

7. Cystidia>35 μm long, basidiospores ellipsoid····S. xanthum

7. Cystidia<35 μm long, basidiospores Cylindrical········································································ S. fissurutum

8. Skeletocystidia absent···········································S. hirsutum

8. Skeletocystidia present····························································9

9. Skeletocystidia subulate, apex acute···································10

9. Skeletocystidia clavate, apex blunt······································12

10. Basidiospores >5 μm wide, aculei >1.5 mm long···················································································S. oreophilum

10. Basidiospores <5 μm wide, aculei <1.5 mm long·········11

11. Basidiomata surface reddish to brick, basidiospores <2 μm wide················································································S. laeticolor

11. Basidiomata surface white to buff, basidiospores >2 μm wide····················································································S. subulatum

12. Basidiomata resupinate························································13

12. Basidiomata effused-reflexed··············································16

13. Basidiomata with broom-like rhizomorphs···················································Etheirodon fimbriatum

13. Basidiomata without broom-like rhizomorphs···············14

14. Basidiospores <2 μm wide·································S. mukhinii

14. Basidiospores >2 μm wide··················································15

15. Aculei <0.5 mm long, aculei <4 per mm··················································································S. tenuissimum

15. Aculei >0.5 mm long, aculei >4 per mm·····S. ochraceum

16. Sterile margin fimbriate······················································17

16. Sterile margin not fimbriate··············································18

17. Basidiospores <3.5 μm wide···························S. yunnanense

17. Basidiospores >3.5 μm wide····························S. elongatum

18. Basidiospores <4 μm long·················································19

18. Basidiospores >4 μm long·················································25

19. Aculei <2 mm long·····························································20

19. Aculei >2 mm long·····························································23

20. Aculei >0.5 mm long··························································21

20. Aculei <0.5 mm long··························································22

21 Basidiospores <2 μm wide····························S. subcollabens

21 Basidiospores >2 μm wide····························S. subtropicum

22. Basidiospores subcylindrical to allantoid················································································S. puerense

22. Basidiospores ellipsoid······································S. cremicolor

23. Aculei 3–4 mm long, pileus margin sharp ····································································Metuloidea murashkinskyi

23. Aculei up to 2 mm long, pileus margin blunt···············24

24. Basidiospores >1.5 μm wide····························S. rawakense

24. Basidiospores <1.5 μm wide························S. confragosum

25. Basidiospores subglobose····················································26

25. Basidiospores ellipsoid························································27

26. Aculei <2 mm long, basidiospores with a normal guttule or not··············································································S. subglobosum

26. Aculei >2 mm long, basidiospores with a distinct guttule···················································································S. hydneum

27. Basidia <11 μm long····························S. rubigimaculatum

27. Basidia >11 μm long····························································28

28. Basidiospores >3 μm wide································S. bourdotii

28. Basidiospores <3 μm wide···················································29

29. Aculei >0.5 mm long, pinkish buff to clay buff························································································S. robustius

29. Aculei <0.5 mm long, cream to pale buff·······················································································S. ciliolatum

Data availability statement

The datasets presented in this study can be found in online repositories. The names of the repository/repositories and accession number(s) can be found in the article/supplementary material.

Author contributions

Conceptualization, C-LZ; methodology, C-LZ and J-HD; software, C-LZ and J-HD; validation, C-LZ and J-HD; formal analysis, C-LZ and J-HD; investigation, C-LZ, Z-LZ, and J-HD; resources C-LZ; writing—original draft preparation, C-LZ, J-HD, X-CZ, and J-JC; writing—review and editing, C-LZ and J-HD; visualization, C-LZ and J-HD; supervision, C-LZ; project administration, C-LZ; funding acquisition, C-LZ and Z-LZ. All authors have read and agreed to the published version of the manuscript.

Funding Statement

The research was supported by the National Natural Science Foundation of China (Project No. 32170004), Natural Science Foundation of the Jiangsu Higher Education Institutions of China (Grant 20KJB220003), Yunnan Fundamental Research Project (Grant No. 202001AS070043), the High-level Talents Program of Yunnan Province (YNQR-QNRC-2018-111).

Abbreviations

ITS, internal transcribed spacer; nLSU, large subunit; SWFC, herbarium of Southwest Forestry University, Kunming, China; KOH, 5% potassium hydroxide; CB, Cotton Blue; CB–, acyanophilous; IKI, Melzer’s reagent; IKI–, both inamyloid and indextrinoid; L, mean spore length (arithmetic average for all spores); W, mean spore width (arithmetic average for all spores); Q, variation in the L/W ratios between The studied specimens, n (a/b), number of spores (a) measured from given number (b) of specimens, spore measurements do not include ornamentation; CTAB, cetyltrimethylammonium bromide; DNA, deoxyribonucleic acid; PCR, polymerase chain reaction; MP, maximum parsimony; ML, maximum likelihood; BI, Bayesian inference; TBR, tree-bisection reconnection.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Availability Statement

The datasets presented in this study can be found in online repositories. The names of the repository/repositories and accession number(s) can be found in the article/supplementary material.

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