The studied specimens are deposited in the fungoria of the Institute of Microbiology, Beijing Forestry University (BJFC) and the Institute of Applied Ecology, Chinese Academy of Sciences (IFP), Museum Vysociny Jihlava, Czech Republic (MJ), herbarium of V.N. Karazin National University, Kharkiv, Ukraine (CWU), the private fungorium of Josef Vlasák (JV), which will be later deposited at the National Museum Prague of Czech Republic (PRM). Morphological descriptions are conducted based on field notes and fungoria specimens. The microscopic analysis refers to Miettinen et al. (2018) and Wu et al. (2022). Sections were studied at a magnification of up to ×1,000 using a Nikon Eclipse 80i microscope and phase contrast illumination. Microscopic features and measurements were made from slide preparations stained with Cotton Blue and Melzer’s reagent. Spores were measured from sections cut from the tubes. To represent variations in the size of spores, 5% of measurements were excluded from each end of the range and are given in parentheses. In the description, KOH = 5% potassium hydroxide, IKI = Melzer’s reagent, IKI− = neither amyloid nor dextrinoid, CB = Cotton Blue, CB+ = cyanophilous in Cotton Blue, CB− = acyanophilous in Cotton Blue, L = arithmetic average of spore length, W = arithmetic average of spore width, Q = L/W ratios, and n = number of basidiospores/measured from given number of specimens. Color terms are recognized from Anonymous (1969) and Petersen (1996).

A Hexadecyl trimethyl ammonium bromide (CTAB) rapid plant genome extraction kit-DN14 (Aidlab Biotechnologies Co., Ltd, Beijing) was used to obtain DNA from dried specimens and to perform the polymerase chain reaction (PCR) according to the manufacturer’s instructions with some modifications (Li et al., 2014; Shen et al., 2019). Two DNA gene fragments, i.e., internal transcribed spacer (ITS) and large subunit nuclear ribosomal RNA gene (nLSU), were amplified using the primer pairs ITS5/ITS4 and LR0R/LR7 (White et al., 1990; Hopple and Vilgalys, 1999) (http://www.biology.duke.edu/fungi/mycolab/primers.htm). The PCR procedure for ITS was as follows: initial denaturation at 95°C for 3 min, followed by 34 cycles of denaturation at 94°C for 40 s, annealing at 54°C for 45 s, and extension at 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 34 cycles of denaturation at 94°C for 30 s, annealing at 50°C for 1 min, and extension at 72°C for 1.5 min, and a final extension at 72°C for 10 min. All sequences analyzed in this study are listed in Table 1 .

In this study, one combined matrix was reconstructed for phylogenetic analysis and a two-gene dataset (ITS + nLSU) was used to determine the phylogenetic position of new species. The sequence alignments and retrieved topologies were deposited in TreeBase (http://www.treebase.org), under accession ID: 30342 (Reviewer access URL: http://purl.org/phylo/treebase/phylows/study/TB2:S30342?x-access-code=32520482eef1e868d55c54893e12e2e3&format=html). Sequences of Exidiopsis calcea KHL 11075, obtained from GenBank, were used as the outgroup (Wu et al., 2017). Phylogenetic analyses were carried out using the approaches of Han et al. (2016) and Zhu et al. (2019). Maximum likelihood (ML) and Bayesian inference (BI) analyses were performed based on the two datasets. The best-fit evolutionary model was selected by hierarchical likelihood ratio tests (HLRTs) and Akaike information criterion (AIC) in MrModeltest 2.2 (Nylander, 2004) after scoring 24 models of evolution in PAUP* v.4.0b10 (Swofford, 2002).

Sequences were analyzed using ML with RAxML-HPC2 through the CIPRES Science Gateway (www.phylo.org; Miller et al., 2009). Branch support (BT) for ML analysis was determined by 1,000 bootstrap replicates. Bayesian phylogenetic inference and Bayesian posterior probabilities (BPPs) were computed with MrBayes v.3.1.2 (Ronquist and Huelsenbeck, 2003). Four Markov chains were run for 1,000,000 generations (two-gene dataset) until the split deviation frequency value was less than 0.01, and trees were sampled every 100 generations. The first 25% of the sampled trees were discarded as burn-in, and the remaining ones were used to reconstruct a majority rule consensus and calculate the BPP of the clades. All trees were viewed in FigTree v.1.4.3 (http://tree.bio.ed.ac.uk/software/figtree/). Branches that received bootstrap supports for ML [≥75% (ML-BS)], and BPP (≥0.95 BPP) were considered as significantly supported. The ML bootstrap (ML) ≥ 50% and BBP (BPP) ≥ 0.90 are displayed on topologies from ML analyses, respectively.

The combined two-gene dataset (ITS + nLSU) included sequences from 98 samples representing 45 taxa. The dataset had an aligned length of 2,244 characters, of which 1,296 (58%) characters were constant, 174 (8%) were variable and parsimony uninformative, and 774 (34%) were parsimony informative. The phylogenetic reconstruction performed with ML and BI analyses for two combined datasets showed similar topology and few differences in statistical support. The best model-fit applied in the Bayesian analysis was GTR + I + G, lset nst = 6, rates = invgamma, and prset statefreqpr = dirichlet (1, 1, 1, 1). Bayesian analysis resulted in a nearly congruent topology with an average standard deviation of split frequencies as 0.005047 to ML analysis, and thus, only the ML tree is provided ( Figure 1 ). The phylogeny reveals that Rigidoporus belongs to Hymenochaetales and Physisporinus belongs to Polyporales. There form three independent lineages in Rigidoporus as new species.

Rigidoporus Murrill, Bull. Torrey bot. Club 32(9): 478 (1905) — MycoBank: MB18478

Type species. — Rigidoporus microporus (Sw.) Overeem, Icon. Fung. Malay. 5: 1 (1924).

Synonymy. — Polyporus micromegas Mont., Ann. Sci. Nat., Bot., sér. 2 17: 128 (1842).

Basidiomata annual to perennial, resupinate, effused-reflexed to pileate or stipitate, soft to corky when fresh, becoming soft corky to hard when dry. Pileal surface cinnamon to fawn, glabrous or velutinate, azonate or concentrically zonate and sulcate. Pore surface white, fawn, orange to brown black. Hyphal system monomitic to pseudo-dimitic; generative hyphae simple septate, thin- to thick-walled, sometimes subsolid. Hyphoid or hymenial cystidia mostly present, thin- to thick-walled, usually apically encrusted; mammillate cystidioles sometimes present. Basidiospores ovoid, ellipsoid to globose, hyaline, thin- to thick-walled, sometimes with one big guttule, IKI−, CB− or weakly CB+. Causing a white rot.

Notes. — Rigidoporus is a cosmopolitan genus growth on both angiosperm and gymnosperm woods (Wu et al., 2022). Up to now, 54 taxa in Rigidoporus and 18 taxa in Oxyporus are recorded in Index Fungorum (http://www.indexfungorum.org/), and among them, 18 species have available DNA sequences ( Table 2 ). In this study, three new species are described and illustrated.

Rigidoporus imbricatus Chao G. Wang, Jing Si & Y.C. Dai, sp. nov. — MycoBank: MB848605; Figures 2 , 3 .

Etymology. — Imbricatus (Lat.), refers to the species having distinct imbricate basidiomata.

Holotype. — China. Yunnan Province, Mengla County, Wangtianshu Nature Reserve, on fallen angiosperm trunk, 18.VI.2017, Dai 17515 (BJFC025047).

Additional specimen examined. — Malaysia, Selangor, Kota Damansara, Community Forest Reserve, on dead angiosperm tree, 7.XII.2019, Dai 21180 (BJFC032834).

Fruiting body. — Basidiomata annual, effused-reflexed to pileate, corky, without odor or taste when fresh, becoming hard corky upon drying, up to 5 cm long, 4 cm wide when resupinate; pilei applanate to flabelliform, projecting up to 6 cm, 12 cm wide and 14 mm thick at base. Pileal surface yellowish brown to brownish orange when fresh, cinnamon to fawn, glabrous, concentrically zonate and sulcate, sometimes tuberculate when dry; margin blunt. Pore surface clay pink to flesh pink when fresh, becoming orange brown upon bruising, eventually honey-yellow to grayish brown when dry; sterile margin distinct, white when fresh, buff yellow when dry, up to 2.5 mm wide; pores round to angular, 7−9 per mm; dissepiments thin, entire to slightly lacerate. Context buff, corky when dry, up to 6 mm thick. Tubes stratified, cream near the context part, concolorous with pore surface near the pores part, hard corky when dry, up to 8 mm long.

Hyphal structure. — Hyphal system monomitic; generative hyphae simple septate, hyaline to yellowish, smooth, IKI−, CB−; tissues becoming black in KOH.

Context. — Contextual hyphae thick-walled with a wide lumen, rarely branched, rarely simple septate, straight to slightly flexuous, interwoven, 4−6 µm in diam.

Tubes. — Tramal hyphae distinctly thick-walled with a wide lumen, unbranched, straight to slightly flexuous, subparallel along the tubes, strongly agglutinated, 3−5.5 µm in diam. Cystidia absent; cystidioles ventricose with a pointed tip, thin-walled, smooth, 15−17 × 5−8 µm; basidia broadly clavate to barrel-shaped, bearing four sterigmata and a simple basal septum, 12−13 × 5−6 µm; basidioles of similar shape to basidia, but smaller.

Spores. — Basidiospores broadly ellipsoid to subglobose, hyaline, thin-walled, smooth, IKI−, CB−, (3.2−)3.4−4 × (2.7−)2.8−3.2(−3.5) µm, L = 3.64 µm, W = 3.05 µm, Q = 1.17−1.21 (n = 60/2).

Notes. — R. imbricatus is characterized by annual and imbricate basidiomata, concentrically zonate and sulcate upper surface, clay pink to flesh pink pore surface when fresh, ventricose cystidioles, broadly ellipsoid to subglobose, thin-walled basidiospores measuring 3.4−4 × 2.8−3.2 µm, and occurrence in tropical Asia.

R. imbricatus, R. aurantiacus Ryvarden & Iturr., and R. pterocaryae are phylogenetically related ( Figure 1 ) but different in morphology. R. aurantiacus has deep-orange to ochraceous pore surface, globose basidiospores measuring 3 × 4 µm, and occurrence in South America (Ryvarden and Iturriaga, 2003). R. pterocaryae has azonate and smooth upper surface and larger thick-walled basidiospores (6.8−7.2 × 5.8−6.8 µm vs. 3.4−4 × 2.8−3.2 µm).

R, dimiticus (Corner) T. Hatt., R. malayanus (Corner) T. Hatt., and R. pendulus Ryvarden were originally described from Southeast Asia and have effused-reflexed to pileate or stipitate basidiomata. However, R. dimiticus has a dimitic hyphal system and larger basidiospores (4−4.7 × 3.5−4 µm vs. 3.4−4 × 2.8−3.2 µm; Hattori, 2001a); R. malayanus has effused-reflexed basidiomata with azonate upper surface, whitish pore surface, angular pores of 1−3 per mm and larger basidiospores (5−6 × 3−3.5 µm vs. 3.4−4 × 2.8−3.2 µm; Hattori, 2003); R. pendulus has violaceous pore surface when fresh, thick-walled hyphoid cystidia encrusted with crystals and globose basidiospores (3.4−4 µm vs. 3.4−4 × 2.8−3.2 µm; Ryvarden, 1990). Thus, they are all different from R. imbricatus.

Rigidoporus pterocaryae Chao G. Wang, Jing Si & Y.C. Dai, sp. nov. — MycoBank: MB848606; Figures 4 , 5 .

Etymology. — pterocaryae (Lat.), refers to the species growth on Pterocarya sp.

Holotype. — China. Fujian Province, Wuyishan, Wuyi Palace, on living tree of Pterocarya, 29.VIII.2006, Cui 4195 (BJFC002245).

Fruiting body. — Basidiomata annual, pileate, corky, without odor or taste when fresh, becoming hard corky upon drying. Pilei petaloid, projecting up to 6 cm, 6.5 cm wide and 9 mm thick at base. Pileal surface honey yellow, glabrous, azonate, tuberculate when dry; margin irregularly lobed to slightly petaloid, blunt, slightly recurved when dry. Pore surface buff, honey yellow to fawn when dry, shiny; sterile margin distinct, cream when dry, up to 2.5 mm wide; pores round to angular, 7−9 per mm; dissepiments thin, slightly lacerate. Context curry yellow, corky when dry, up to 4 mm thick. Tubes concolorous with pore surface, hard corky when dry, up to 5 mm long.

Hyphal structure. — Hyphal system monomitic; generative hyphae simple septate, hyaline to yellowish, smooth, IKI−, CB+; tissues becoming black in KOH.

Context. — Contextual hyphae slightly thick- to thick-walled with a wide lumen, rarely branched, moderately simple septate, straight to flexuous, interwoven, 3−5 µm in diam.

Tubes. — Tramal hyphae slightly thick-walled with a wide lumen, unbranched, straight to slightly flexuous, subparallel along the tubes, agglutinated, 2.5−4 µm in diam. Cystidia absent; cystidioles ventricose with a pointed tip, thin-walled, smooth, 16−17 × 8−9 µm; basidia broadly barrel-shaped, bearing four sterigmata and a simple basal septum, 12−15 × 10−11 µm; basidioles of similar shape to basidia, but smaller. Rhomboid or irregular hyaline crystals present among hymenium.

Spores. — Basidiospores subglobose, hyaline, thick-walled, smooth, with one big or two small guttules, IKI−, CB−, (6.2−)6.8−7.5(−7.8) × (5.5−)5.8−7(−7.2) µm, L = 7.2 µm, W = 6.21 µm, Q = 1.15 (n = 30/1).

Notes. — R. pterocaryae is characterized by annual and pileate basidiomata, petaloid pilei, azonate and smooth upper surface, buff, honey yellow to fawn pore surface when dry, ventricose cystidioles, subglobose, thick-walled basidiospores measuring 6.8−7.5 × 5.8−7 µm, and growth on Pterocarya in China.

R. pterocaryae and R. ulmarius (Sowerby) Imazeki are similar in morphology, and share pileate basidiomata, azonate upper surface, subglobose, thick-walled, and almost the same size of basidiospores (this study). However, the latter has concentrically sulcate upper surface, and phylogenetically, they are distantly related ( Figure 1 ).

One sequence of sample d1 from China was identified as R. ulmarius in GenBank (GenBank accession NO. KC414238). In our phylogenetic analysis, it nested together with R. pterocaryae.

Rigidoporus subcorticola Chao G. Wang, Jing Si & Y.C. Dai, sp. nov. — MycoBank: MB848607; Figures 6 , 7 .

Etymology. — subcorticola (Lat.), refers to the species being similar to R. corticola.

Holotype. — China. Beijing, Xiaolongmen Forest Park, on fallen angiosperm trunk, 30.VIII.2022, Dai 24419 (BJFC039662).

Additional specimens examined. — China. Heilongjiang Province, Ning’an County, Jingpo Lake Forest Park, on Pinus koraiensis, Dai 8895 (IFP 011351); Henan Province, Neixiang County, Baotianman Nature Reserve, on Juglans sp., 23.IX.2009, Dai 11319 (BJFC007465).

Fruiting body. — Basidiomata annual, resupinate to effused-reflexed, soft, without odor or taste when fresh, becoming soft corky upon drying, up to 8 cm long and 2 cm wide when resupinate; pilei flabelliform, projecting up to 1.7 cm, 3 cm wide, 3 mm thick at base. Pileal surface white to cream when fresh, becoming cream to pinkish buff, glabrous, azonate and tuberculate upon drying; margin slightly acute. Pore surface white to cream when fresh, becoming cream to buff yellow upon drying; sterile margin white to cream when fresh, buff when dry, thinning out, somewhat incised, up to 1 mm wide; pores angular, 2−4 per mm; dissepiments thin, lacerate. Context cream, soft corky when dry, up to 0.4 mm thick. Tubes concolorous with pore surface, soft corky when dry, up to 0.8 mm long.

Hyphal structure. — Hyphal system monomitic; generative hyphae simple septate, hyaline, IKI−, CB+; tissues unchanged in KOH.

Context. — Contextual hyphae thick-walled with a wide lumen, occasionally branched, straight to flexuous, interwoven, 3−6 µm in diam.

Tubes. — Tramal hyphae thick-walled with a wide lumen, occasionally branched, straight to flexuous, subparallel along the tubes, 2−3.5 µm in diam. Cystidia present, arising from tramal hyphae and projecting from the hymenium, thick-walled, apically encrusted with crown crystals, 15−16 × 4.5−5 µm; cystidioles fusoid to ventricose, thin-walled, smooth or encrusted with tiny crystals, 12−15 × 5−6 µm; basidia barrel-shaped, with four sterigmata and a simple basal septum, 14−16 × 5.5−7 µm; basidioles of similar shape to basidia.

Spores. — Basidiospores oblong ellipsoid to ellipsoid, hyaline, thin-walled, smooth, IKI−, weakly CB+, 5−5.8(−6) × 3−4 µm, L = 5.44 µm, W = 3.48 µm, Q = 1.56 (n = 30/1).

Notes. — R. subcorticola is characterized by annual, resupinate to effused-reflexed basidiomata, azonate and tuberculate upper surface, cream to buff yellow pore surface when dry, big angular pores of 2−4 per mm, thick-walled and encrusted hymenial cystidia, fusoid to ventricose cystidioles, oblong ellipsoid to ellipsoid basidiospores measuring 5−5.8 × 3−4 µm, and often occur in the north temperate zone.

R. subcorticola and R. macroporus (Y.C. Dai & Y.L. Wei) F. Wu et al. are closely related in our phylogeny ( Figure 1 ), share cream to buff yellow pore surface, clavate to ventricose cystidioles, and ellipsoid basidiospores, as well as are distributed in China. However, the later has resupinate basidiomata, thin-walled tramal hyphae and larger basidiospores (7−8 × 3.5−4.1 µm vs. 5−5.8 × 3−4 µm; Dai et al., 2004). R. subcorticola and R. corticola (Fr.) Pouzarare are very similar in morphology and share resupinate to effused-reflexed basidiomata with light-colored pore surface and ellipsoid basidiospores (5−6 × 3.5−4.5 µm vs. 5−5.8 × 3−4 µm; Ryvarden and Gilbertson, 1994). However, the latter has slightly zonate and somewhat radially wrinkled upper surface. The three species form different independent lineages in Rigidoporus ( Figure 1 ).

Rigidoporus millavensis (Bourdot & Galzin) Chao G. Wang, Jing Si & Y.C. Dai, comb. et stat. nov. — MycoBank: MB848608; Figure 8 .

Basionym. — Poria mucida subsp. millavensis Bourdot & Galzin, Bull. trimest. Soc. mycol. Fr. 41(2): 238 (1925)

≡ Oxyporus millavensis (Bourdot & Galzin) Ryvarden & Melo, Syn. Fung. (Oslo) 31: 293 (2014).

Specimens examined. — China. Gansu Province, Zhangye, Qilianshan Nature Reserve, on the dead tree of Juniperus przewalskii, Dai 18970 (BJFC027439); Inner Mongolia, Alxa County, Helanshan Nature Reserve, on the fallen branch of Picea, Dai 24509 (BJFC039751); on the fallen trunk of Picea, Dai 24503 (BJFC039745); Xinjiang, Xinyuan County, Nalati Nature Reserve, on the fallen trunk of Populus euphratica, Wei 1622 (BJFC010351).

Descriptions for one known species and one uncertain species

Rigidoporus microporus — Figures 9 and 10

Specimens examined. — Brazil. Manaus, parque Municipal Cachoeira das Orquídeas, on a fallen angiosperm trunk, 12.V.2017, Dai 17402 (BJFC024937); Dai 17392 (BJFC024928).

Fruiting body. — Basidiomata annual to perennial, resupinate, effused-reflexed to pileate, corky, without odor or taste when fresh, becoming hard corky upon drying, up to 6 cm long, 5 cm wide when resupinate; pilei flabelliform, projecting up to 6 cm, 7.5 cm wide and 4 mm thick at base. Pileal surface cinnamon to fawn, glabrous, concentrically zonate and sulcate when dry; margin acute. Pore surface fawn to reddish brown when dry; sterile margin thinning out, pinkish buff when dry; pores round to angular, 12−14 per mm; dissepiments thin, entire to lacerate. Context buff, corky when dry, up to 1 mm thick. Tubes honey yellow to fawn when dry, paler than pore surface, hard corky when dry, up to 3 mm long.

Hyphal structure. — Hyphal system monomitic; generative hyphae simple septate, hyaline, smooth, IKI−, weakly CB+; tissues becoming black in KOH.

Context. — Contextual hyphae thick-walled with a wide lumen, unbranched, rarely simple septate, straight to slightly flexuous, interwoven, 3.5−5.5 µm in diam.

Tubes. — Tramal hyphae distinctly thick-walled with a wide lumen, unbranched, straight to slightly flexuous, subparallel along the tubes, strongly agglutinated, 3.5−5 µm in diam. Cystidia absent; cystidioles ventricose with a pointed tip, thin-walled, smooth, 10−15 × 7−8 µm; basidia broadly clavate to barrel-shaped, bearing four sterigmata and a simple basal septum, 10−12 × 4.5−6 µm; basidioles of similar shape to basidia, but smaller. Rhomboid or irregular crystals sometimes present among hymenium.

Spores. — Basidiospores broadly ellipsoid to subglobose, hyaline, thin-walled, smooth, IKI−, CB−, (3.6−)3.8−4.3 × (3−)3.2−3.8(−4) µm, L = 3.98 µm, W = 3.42 µm, Q = 1.16−1.17 (n = 60/2).

“Rigidoporus ulmarius” — Figures 11 and 12

Specimen examined. — French Guiana. Roura, Amazon Lodge, 2.IX.2019, JV 1909/17-J (JV, isotype in BJFC033010).

Fruiting body. — Basidiomata annual, pileate, corky, without odor or taste when fresh, becoming hard corky upon drying. Pilei flabelliform, projecting up to 8 cm, 15 cm wide and 7 mm thick at base. Pileal surface buff to cinnamon buff, glabrous, azonate, distinctly radially wrinkled to ribbed and slightly squamose when dry; margin acute, incurved when dry. Pore surface clay buff to fawn when dry; sterile margin indistinct, almost absent; pores angular, 8−10 per mm; dissepiments thin, slightly lacerate. Context ochraceous, corky when dry, up to 3 mm thick. Tubes concolorous with pore surface, distinctly deeper-colored than the context, hard corky when dry, up to 4 mm long.

Hyphal structure. — Hyphal system monomitic; generative hyphae simple septate, yellowish, smooth, IKI−, CB−; tissues unchanged in KOH.

Context. — Contextual hyphae thick-walled with a wide lumen, unbranched, moderately simple septate, more or less flexuous, interwoven, 3−6 µm in diam.

Tubes. — Tramal hyphae distinctly thick-walled with a wide lumen, unbranched, flexuous, subparallel along the tubes, 3.5−6 µm in diam. Cystidia absent; cystidioles ventricose with a pointed tip, thin-walled, smooth, 14−17 × 6−8 µm; basidia broadly barrel-shaped, bearing four sterigmata and a simple basal septum, 15−17 × 9−10 µm; basidioles of similar shape to basidia but smaller. Rhomboid or irregular hyaline crystals present among hymenium.

Spores. — Basidiospores subglobose, sometimes collapsed, hyaline, slightly thick-walled, smooth, sometimes with one big guttule, IKI−, CB+, (5.5−)6−7 × 5−6.2(−6.3) µm, L = 6.36 µm, W = 5.66 µm, Q = 1.12 (n = 30/1).