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.

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 .

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 ).

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).

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.

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.

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

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 .

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 .

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).

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