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Phylogeny and taxonomy of Laetiporus (Basidiomycota, Polyporales) with descriptions of two new species from western China
expand article infoJie Song§, Yi-Fei Sun, Xing Ji, Yu-Cheng Dai, Bao-Kai Cui
‡ Beijing Forestry University, Beijing, China
§ Research Institute of Tropical Forestry, Chinese Academy of Forestry, Guangzhou, China
Open Access

Abstract

Laetiporus is a cosmopolitan genus of brown rot fungi. In this study, L. medogensis and L. xinjiangensis are described as new species from western China, based on morphological and molecular evidence. L. medogensis has only been found on gymnosperms so far and is distinguished by pinkish-buff to clay-buff pileal surface and buff-yellow pore surface, azonate to faintly zonate pileus and ellipsoid to ovoid basidiospores (5–6.2 × 4.2–5.2 μm). L. xinjiangensis is found on angiosperms and is characterised by pale-buff to clay-pink pileal surface, cream to light yellow pore surface, azonate to faintly zonate pileus, large pores (2–3 per mm) and small basidiospores (4.5–5 × 3–4.2 μm). The phylogeny of Laetiporus is reconstructed with multi-gene sequences including the internal transcribed spacer regions (ITS), the large subunit (nrLSU) and small subunit (nrSSU) of the nuclear ribosomal RNA gene, the small subunit of the mitochondrial rRNA gene (mtSSU), the translation elongation factor 1-α gene (EF-1α) and the second subunit of RNA polymerase II (RPB2). The results show that L. medogensis and L. xinjiangensis formed two distinct lineages belonging to Laetiporus. Illustrated descriptions of the two new species are presented. An identification key to species of L. sulphureus complex is provided.

Keywords

Brown-rot fungi, multi-gene phylogeny, Fomitopsidaceae, taxonomy, wood-decaying fungi

Introduction

Laetiporus Murrill (Fomitopsidaceae, Polyporales) is a cosmopolitan genus, causing brown rot on living hardwoods and conifers (Murrill 1904). Some species of the genus are known as forest pathogens and some are edible with medicinal functions (Dai et al. 2007, 2009). According to previous studies, 15 species have been accepted in the genus worldwide and 11 species have been confirmed in the L. sulphureus complex by phylogenetic analyses, of which six have been reported from China: L. ailaoshanensis B.K. Cui & J. Song, L. cremeiporus Y. Ota & T. Hatt., L. montanus Černý ex Tomšovský & Jankovský, L. sulphureus (Bull.) Murrill, L. versisporus (Lloyd) Imazeki and L. zonatus B.K. Cui & J. Song (Tomšovský and Jankovský 2008, Ota et al. 2009, Banik et al. 2012, Song et al. 2014, Song and Cui 2017). The species in the L. sulphureus complex are characterised by annual basidiocarps, soft and fleshy context and a dimitic hyphal system composed of simple septate generative hyphae and binding hyphae (Burdsall and Banik 2001, Núñez and Ryvarden 2001, Ota et al. 2009).

A molecular phylogenetic study of Laetiporus in Japan identified three species, viz. L. cremeiporus, L. montanus and L. versisporus (Ota and Hattori 2008, Ota et al. 2009). Recently, systematic studies have been carried out to define the species and explore the historical biogeography of the genus Laetiporus in China. Song et al. (2014) described two new Laetiporus species from south-western China based on morphological and molecular evidence. Further comprehensive study of Song and Cui (2017) indicated that there are two additional undescribed Laetiporus species.

In the present study, the two new Laetiporus species from western China (Clade P and Clade Q) are described based on morphological and phylogenetic analyses.

Materials and methods

Morphological studies

Morphological studies followed Han et al. (2016). The studied specimens were deposited in the herbarium of the Institute of Microbiology, Beijing Forestry University (BJFC). Macro-morphological descriptions were based on field notes. Colour terms followed Petersen (1996). Microscopic measurements and drawings were made from slide preparations of dried specimens stained with Cotton Blue and Melzer’s reagent, following Han et al. (2016). Sections were studied at a magnification of 1000× using a Nikon Eclipse 80i microscope and phase contrast illumination. Drawings were made with the aid of a drawing tube. Spores were measured in tube sections. In presenting spore size variation, 5% of measurements were excluded from each end of the range and given in parentheses. The following abbreviations were used: KOH = 5% potassium hydroxide, CB = cotton blue, CB+ = cyanophilous, CB– = acyanophilous, IKI = Melzer’s reagent, IKI– = neither amyloid nor dextrinoid, L = mean spore length (arithmetic average), W = mean spore width (arithmetic average), Q = variation in the L/W ratios between specimens studied, n (a/b) = number of spores (a) measured from a given number of specimens (b).

Molecular study and phylogenetic analysis

Genomic DNA was extracted from dried fruiting bodies using a cetyltrimethylammonium bromide rapid plant genome extraction kit (Aidlab Biotechnologies Co., Ltd., Beijing) according to the manufacturer’s instructions with some modifications (Han et al. 2016). Six genetic markers were used, including ITS, nrLSU, nrSSU, EF-1α, mtSSU and RPB2. The primer pairs ITS5/4, LR0R/LR7, MS1/MS2, NS1/NS4, 983F/1567R and 6F/7R were used to amplify ITS, nrLSU, mtSSU, nrSSU, EF-1α and RPB2, respectively (http://www.biology.duke.edu/fungi/mycolab/primers.htm). A 2 × EasyTaq PCR SuperMix (Transgen Biotech, Beijing) was used to amplify the genes. The PCR procedure for ITS, EF-1α, mtSSU and RPB2 was as follows: initial denaturation at 95 °C for 3 min, followed by 35 cycles at 94 °C for 40 s, 54 °C for 45 s and 72 °C for 1 min and a final extension of 72 °C for 10 min. The PCR procedure for nrLSU and nrSSU was as follows: initial denaturation at 94 °C for 1 min, followed by 35 cycles at 94 °C for 30 s, 50 °C for 1 min and 72 °C for 1.5 min and a final extension of 72 °C for 10 min. The PCR products were purified using the Bioteke DNA Purification Kit (Bioteke Corporation, Beijing) and sequenced at the Beijing Genomics Institute, China, with the same primers. The basic authenticity and reliability of newly generated sequences were established based on Nilsson et al. (2012). The newly generated sequences and additional sequences downloaded from GenBank (www.ncbi.nlm.nih.gov/genbank; Benson et al. 2017) are listed in Table 1. Sequences of ITS, nrLSU, nrSSU, EF-1α, mtSSU and RPB2 of species in Laetiporus and outgroups [Antrodia serialis (Fr.) Donk and Fomitopsis pinicola (Sw.) P. Karst.] were combined and aligned in MAFFT 7 (Katoh and Toh 2008; https://mafft.cbrc.jp/alignment/server/index.html) using the “G-INS-I” strategy and manually adjusted in BioEdit v7.2.6.1 (Hall 1999).

A list of species, specimens and GenBank accession numbers of sequences used in this study.

Species Collection no. GenBank Accessions
ITS nrLSU nuSSU mtSSU EF-1α RPB2
Antrodia serialis Cui 10519 KP715307 KP715323 KR605911 KR606011 KP715337 KR610830
Fomitopsis pinicola Cui 10405 KC844852 KC844857 KR605857 KR605961 KR610690 KR610781
Laetiporus ailaoshanensis Dai 13567 (Paratype) KX354470a KX354498a KX354535a KX354577a KX354623a KX354665a
L. ailaoshanensis Dai 13256 (Holotype) KF951289a KF951317a KX354537a KX354579a KX354625a KT894786a
L. caribensis PR 6583 JN684766 - - - - -
L. caribensis PR 914 JN684762 EU402526 - EU402482 - -
L. caribensis PR 6521 JN684771 - - - - -
L. cincinnatus Dai 12811 KF951291a KF951304a KX354516a KX354558a KX354605a KT894788a
L. cincinnatus DA 37 EU402557 EU402521 - EU402485 AB472661 -
L. cincinnatus JV 0709/168J KF951290a KF951305a KX354517a KX354559a KX354606a KX354651a
L. conifericola JV 0709/81J KF951292a KF951327a KX354531a KX354573a KX354683a
L. conifericola CA 8 EU402575 EU402523 - EU402487 AB472663 -
L. conifericola JAM 1 EU402577 EU402524 - EU402486 AB472664 -
L. cremeiporus Dai 10107 KF951281a KF951301a KX354515a KX354557a KX354604a KX354650a
L. cremeiporus Cui 10991 KF951279a KF951298a - KX354595a KX354641a KX354679a
L. cremeiporus Cui 10586 KF951277a KF951297a KX354513a KX354555a KX354602a KX354648a
L. gilbertsonii JV 1109/31 KF951293a KF951306a KX354542a KX354584a KX354630a KX354671a
L. gilbertsonii TJV 2000/101 EU402553 EU402528 - EU402493 AB472668 -
L. gilbertsonii CA 13 EU402549 EU402527 - EU402496 AB472666 -
L. huroniensis HMC 3 EU402571 EU402540 - - - -
L. huroniensis MI 14 EU402573 EU402539 - EU402489 AB472672 -
L. medogensis Cui 12219 (Paratype) KX354472a KX354500a KX354538a KX354580a KX354626a KX354667a
L. medogensis Cui 12240 (Holotype) KX354473a KX354501a KX354539a KX354581a KX354627a KX354668a
L. medogensis Cui 12390 (Paratype) KX354474a KX354502a KX354540a KX354582a KX354628a KX354669a
L. montanus Dai 15888 KX354466a KX354494a KX354530a KX354572a KX354619a KX354662a
L. montanus Cui 10011 KF951274a KF951315a KX354528a KX354570a KX354617a KT894790a
L. montanus Cui 10015 KF951273a KF951311a KX354529a KX354571a KX354618a KT894791a
L. sp. 1 EUC 1 EU402545 EU402541 - - - -
L. sp. 1 KOA 1 EU402546 EU402542 - - - -
L. sp. 2 RV4A EU840662 - - - - -
L. sp. 2 RV5A EU840663 - - - - -
L. sp. 3 Munez 207 JN684764 - - - - -
L. sp. 4 Robledo 1122 JN684765 - - - - -
L. sulphureus Cui 12389 KR187106a KX354487a KX354519a KX354561a KX354608a KX354653a
L. sulphureus Cui 12388 KR187105a KX354486a KX354518a KX354560a KX354607a KX354652a
L. sulphureus Dai 12154 KF951295a KF951302a KX354521a KX354563a KX354610a KX354655a
L. sulphureus Z.R.L. CA04 KX354479a KX354506a KX354545a KX354587a KX354633a KX354674a
L. sulphureus Z.R.L. CA08 KX354480a KX354507a KX354546a KX354588a KX354634a KX354675a
L. sulphureus DA 41 EU40256 EU402533 - EU402481 AB472660 -
L. sulphureus TJV 99/150 EU402567 EU402530 - EU402492 - -
L. sulphureus MAS 2 EU402568 EU402531 - EU402491 - -
L. sulphureus JV 1106/15 KF951296a KF951303a KX354520a KX354562a KX354609a KX354654a
L. versisporus Cui 7882 KF951269a KF951323a - KX354596a KX354642a KT894783a
L. versisporus Li 15071314 KX354476a KX357139a - KX354598a KX354644a KX354680a
L. versisporus Dai 13160 KF951266a KF951320a - KX354597a KX354643a KT894785a
L. versisporus Yuan 6319 KX354475a KX354503a KX354541a KX354583a KX354629a KX354670a
L. versisporus Dai 10992 KF951272a KF951325a - KX354600a KX354646a KX354681a
L. versisporus Dai 13052 KF951271a KF951324a - KX354601a KX354647a KX354682a
L. xinjiangensis Dai 15825 (Paratype) KX354465a KX354493a KX354527a KX354569a KX354616a KX354661a
L. xinjiangensis Dai 15828 (Paratype) KX354461a KX354489a KX354523a KX354565a KX354612a KX354657a
L. xinjiangensis Dai 15953 (Holotype) KX354460a KX354488a KX354522a KX354564a KX354611a KX354656a
L. xinjiangensis Dai 15898A (Paratype) KX354464a KX354492a KX354526a KX354568a KX354615a KX354660a
L. zonatus HKAS 71806 (Paratype) KF951284a KF951310a KX354548a KX354590a KX354636a KT894796a
L. zonatus Cui 10403 (Paratype) KF951282a KF951307a KX354550a KX354592a KX354638a -
L. zonatus Cui 10404 (Holotype) KF951283a KF951308a KX354551a KX354593a KX354639a KT894797a

Bayesian Inference (BI), Maximum Likelihood (ML) and Maximum Parsimony (MP) analyses were applied to the combined dataset. The best fit model of nucleotide evolution to each individual genetic marker and the combined dataset was selected with AIC (Akaike Information Criterion) using MrModeltest 2.3 (Posada and Crandall 1998, Nylander 2004). The best fit models were GTR for ITS, nrLSU, nrSSU, EF-1α, mtSSU, RPB2 and GTR+I+G for the combined dataset. The partitioned mixed model, which allows for model parameters estimated separately for each genetic marker, was used in the Bayesian analysis. BI was performed using MrBayes 3.1.2 (Ronquist and Huelsenbeck 2003) with 2 independent runs, each one beginning from random trees with 4 simultaneous independent chains, performing 4,000,000 replicates, sampling one tree 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 Bayesian posterior probabilities (BPP) of the clades.

ML searches were conducted with RAxML-HPC2 on Abe through the Cipres Science Gateway (www.phylo.org) and comprised 100 ML searches under the GTRGAMMA model, with all model parameters estimated by the programme. Only the maximum likelihood best tree from all searches was kept. In addition, 100 rapid bootstrap replicates were run with the GTRCAT model to assess the reliability of the nodes.

MP analysis was applied to the combined dataset as in Song and Cui (2017). Tree construction was performed in PAUP* version 4.0b10 (Swofford 2002) with the following settings. 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 most parsimonious trees were saved. Clade robustness was assessed using a bootstrap analysis with 1000 replicates (Felsenstein 1985). The descriptive statistics of tree length (TL), consistency index (CI), retention index (RI), rescaled consistency index (RC) and homoplasy index (HI) were calculated for each most parsimonious tree generated.

Branches that received bootstrap support for maximum parsimony (MP), maximum likelihood (ML) and Bayesian posterior probabilities (BPP) greater than or equal to 75% (MP/ML) and 0.95 (BPP) were considered as significantly supported.

Results

Phylogenetic analyses

The combined dataset (ITS+nrLSU+nrSSU+mtSSU+EF-1α+RPB2) included sequences from 55 samples representing 19 taxa. Antrodia serialis and Fomitopsis pinicola were used as outgroups. The dataset had a total aligned length of 3963 characters, of which 3137 (79.2%) were constant, 301 (7.6%) were variable and parsimony uninformative and 525 (13.2%) were parsimony informative. The parsimony analysis yielded 68 equally parsimonious trees (TL = 1173, CI = 0.812, RI = 0.865, RC = 0.702, HI = 0.188). The multiple sequence alignment and tree files were deposited at TreeBase (submission ID 21249; www.treebase.org). MP analysis and BI resulted in similar topologies as the ML analysis. The consensus tree inferred from the ML analysis with MP, ML and BPP values is shown in Figure 1.

Samples of Laetiporus clustered together with significant support (100% MP, 100% ML and 1.00 BPP; Figure 1). Sampled specimens of the two new species L. medogensis and L. xinjiangensis formed well-supported lineages (Figure 1).

Figure 1. 

Strict consensus tree illustrating the phylogeny of Laetiporus generated by ML analysis based on ITS+nrLSU+nrSSU+mtSSU+EF-1α+RPB2 sequences. Branch support is indicated where MP/BS support is greater than 50% and collapsed below that support threshold. BPP is indicated when greater than 0.95. New species are indicated in bold.

Taxonomy

Laetiporus medogensis J. Song & B.K. Cui

MycoBank No: MB821867
Figures 2a, 3

Diagnosis

Differs from other Laetiporus species by its pinkish-buff to clay-buff pileal surface, buff-yellow pore surface and ellipsoid to ovoid basidiospores (5–6.2 × 4.2–5.2 μm).

Etymology

Medogensis (Lat.): referring to the locality (Medog County) of the type specimens.

Holotype

CHINA. Xizang Auto. Reg. (Tibet), Medog County, on living tree of Abies, 21 Sep 2014, Cui 12240 (BJFC 017154).

Basidiocarps

Annual, sessile to laterally substipitate, imbricate, fleshy when fresh, crumbly when dry, without odour or taste. Pileus flabelliform to dimidiate, applanate, projecting up to 9 cm, 12 cm wide and 1 cm thick. Pileal surface pinkish-buff to clay-buff when fresh, becoming pale yellow upon drying, glabrous, azonate to faintly zonate. Margin soft and slightly viscous, fawn when juvenile, fading to reddish-brown when dry. Pore surface buff-yellow when fresh, becoming pale yellow to cream when dry; sterile margin cream when fresh, up to 3 mm wide; pores angular, 2–4 per mm; dissepiments thin, entire to lacerate. Context white when fresh, becoming cream to pale yellow when dry, up to 8.5 mm thick. Tubes concolorous with pore surface, crumbly or chalky, up to 1.5 mm long.

Figure 2. 

Basidiomata of Laetiporus species. a L. medogensis b L. xinjiangensis. Scale bars: a = 2 cm, b = 3 cm.

Hyphal structure

Hyphal system dimitic; generative hyphae simple-septate; skeletal hyphae IKI–, CB–, dissolving in KOH. Generative hyphae in context infrequent, hyaline, thin-walled, occasionally branched, up to 11 µm in diam.; skeletal hyphae in context dominant, thick-walled with a wide lumen, frequently branched and interwoven, occasionally simple-septate, hyaline, 4–11 μm in diam. Generative hyphae in tubes dominant, hyaline, thin-walled, frequently branched, simple-septate, 4–5 µm in diam.; skeletal hyphae in tubes thick-walled with a wide lumen, occasionally branched and simple-septate, subparallel along the tubes, 3–5 µm in diam.

Cystidia

Cystidia and other sterile hyphal elements absent.

Basidia

Basidia clavate, 20–25 × 8–9 μm, bearing four sterigmata and a basal simple-septum; basidioles clavate, smaller than basidia.

Spores

Basidiospores ellipsoid to ovoid, hyaline, thin-walled, smooth, IKI–, CB–, 5–6.2 × 4.2–5.2 μm, L = 5.78 μm, W = 4.73 μm, Q = 1.22–1.23 (n = 60/2).

Additional specimens

(paratypes) examined. CHINA. Xizang Auto. Reg. (Tibet), Medog County, on living tree of Abies, 20 Sep 2014, Cui 12218 (BJFC 017132) & Cui 12219 (BJFC 017133); 21 Sep 2014, Cui 12241 (BJFC 017155); 24 Aug 2014, Cui 12390 (BJFC 017304).

Figure 3. 

Microscopic structures of Laetiporus medogensis (drawn from the holotype). a Basidiospores b Basidia c Basidioles d Hyphae from trama e Hyphae from context.

Laetiporus xinjiangensis J. Song, Y.C. Dai & B.K. Cui

MycoBank No: MB821868
Figures 2b, 4

Diagnosis

Differs from other Laetiporus species by its pale-buff to clay-pink pileal surface, cream to light-yellow pore surface, large pores (2–3 per mm) and smaller basidiospores (4.5–5 × 3–4.2 μm).

Etymology

Xinjiangensis (Lat.): referring to the locality (Xinjiang Autonomous Region) of the type specimens.

Holotype

CHINA. Xinjiang Auto. Reg., Ili Kazak Autonomous Prefecture, Gongliu County, West Tianshan National Nature Reserve, on living tree of Betula, 14 Sep 2015, Dai 15953 (BJFC 020054).

Basidiocarps

Annual, sessile to laterally substipitate, imbricate, odour distinctive, taste with acid flavor, fleshy when fresh, crumbly when dry. Pilei flabelliform to dimidiate, applanate, projecting up to 15 cm, 20 cm wide and 3 cm thick. Pileal surface pale-buff to clay-pink when fresh, becoming pale-buff to cream upon drying, glabrous, azonate to faintly zonate when fresh. Margin blunt, clay-buff to greyish-brown to brown when juvenile, fading to dark brown when dry. Pore surface cream to light yellow when fresh, becoming pale yellow when dry; sterile margin pale yellow when fresh, up to 2 mm wide; pores angular, 2–3 per mm; dissepiments thin, entire to lacerate. Context white when fresh, becoming cream to pale yellow when dry, up to 2.2 cm thick. Tubes concolorous with pore surface, crumbly or chalky, up to 8 mm long.

Hyphal structure

Hyphal system dimitic; generative hyphae simple-septate; skeletal hyphae IKI–, CB–, dissolving in KOH. Generative hyphae in context infrequent, hyaline, thin-walled, occasionally branched, up to 11 µm in diam.; skeletal hyphae in context dominant, hyaline, thick-walled with a wide lumen, frequently branched and interwoven, occasionally simple-septate, 8–15 μm in diam. Generative hyphae in tubes dominant, hyaline, thin-walled, frequently branched, simple-septate, 4–6 µm in diam.; skeletal hyphae in tubes thick-walled with a wide lumen, occasionally branched and simple-septate, subparallel along the tubes or interwoven, 3–5 µm in diam.

Cystidia

Cystidia and other sterile hyphal elements absent.

Basidia

Basidia clavate, 20–25 × 6–8 μm, bearing four sterigmata and a basal simple-septum; basidioles clavate, smaller than basidia.

Spores. Basidiospores ellipsoid to ovoid, hyaline, thin-walled, smooth, IKI–, CB–, 4.5–5 × 3–4.2 μm, L = 4.87 μm, W = 3.65 μm, Q = 1.33–1.37 (n = 60/2).

Additional specimens

(paratypes) examined. CHINA. Xinjiang Auto. Reg., Shihezi, on living tree of Populus, 9 Sep 2015, Dai 15825 (BJFC 019930) & Dai 15828 (BJFC 019931); Burqin County, on living tree of Salix, 9 Sep 2015, Dai 15836 (BJFC 019937) & Dai 15838 (BJFC 019939); Burqin County, Kanas Integrated Nature Landscape Protect Region, on living tree of Salix, 11 Sep 2015, Dai 15893 (BJFC019994); Ili Kazak Autonomous Prefecture, on living tree of Populus, 13 Sep 2015, Dai 15902 (BJFC 020003) & Dai 15905 (BJFC 020006); 4 Oct 2015, Dai 15898A (BJFC 019999).

Figure 4. 

Microscopic structures of Laetiporus xinjiangensis (drawn from the holotype). a Basidiospores b Basidia c Basidioles d Hyphae from trama e Hyphae from context.

Discussion

Recent studies indicated that Laetiporus sulphureus in East Asia is a species complex, comprising several morphologically and ecologically distinct species (Ota et al. 2009, Song et al. 2014). The current study recognised two new species, namely, L. medogensis and L. xinjiangensis and, altogether, eight Laetiporus species have been found in China thus far. The multi-gene phylogenetic topology showed that the new species formed two separate lineages (Figure 1).

Laetiporus medogensis and L. ailaoshanensis group together with moderate to low MP and ML support (50% MP and 53% ML). Both L. medogensis and L. ailaoshanensis are found in Southwest China. Morphologically, L. ailaoshanensis is similar to L. medogensis by producing orange to yellow pileal surface, white context and ellipsoid to ovoid basidiospores. However, L. medogensis is found on conifers and the pore surface is yellow; L. ailaoshanensis grows on hardwoods and has a white pore surface (Song et al. 2014). L. sulphureus resembles L. medogensis by producing yellow to orange pileal surface and yellow pore surface; however, L. sulphureus usually grows on hardwoods and produces thicker basidiocarps and larger basidiospores (5–7 × 4–5 µm; Ota et al. 2009). L. versisporus and L. medogensis share similar characters including yellow pileal surface, yellowish pore surface and ovoid to ellipsoid basidiospores; however, L. versisporus differs from L. medogensis in having smaller pores (2–6 per mm) and larger basidiospores (4–6.8 × 3–5.5 μm). In addition, L. versisporus grows on hardwoods and is mainly distributed in subtropical to tropical areas (Ota et al. 2009, Song and Cui 2017).

Laetiporus xinjiangensis, L. sulphureus and L. montanus are all common in Northwest China. Both L. xinjiangensis and L. sulphureus grow on angiosperms and group together in the phylogenetic tree with moderate MP, ML and significant BI support (65% MP, 51% ML and 0.98 BPP). Morphologically, L. sulphureus is similar to L. xinjiangensis in having yellowish pore surface and ovoid to ellipsoid basidiospores; however, L. sulphureus produces larger basidiospores (5–7 × 4–5 μm) and has smaller pores (2–5 per mm; Burdsall and Banik 2001). L. montanus is similar to L. xinjiangensis by producing a burlywood pileal surface and a yellowish pore surface; however, L. montanus differs by producing pyriform basidiospores (6–8 × 4–5.5 μm) and by growing on gymnosperms (Tomšovský and Jankovský 2008).

Our research expanded the number of Laetiporus species to 17 around the world. However, studies in the Southern Hemisphere are still few and the relationships amongst Laetiporus species remain unresolved (Lindner and Banik 2008, Pires et al. 2016, Song and Cui 2017). More comprehensive studies on Laetiporus depend on more collections and data from poorly sampled areas. The main morphological characters, host trees and distribution areas of species in the L. sulphureus complex are provided in Table 2. An identification key to the known species of Laetiporus is provided.

Key to accepted species in the Laetiporus sulphureus complex

1 Pore surface light goldenrod to sulphur yellow or light yellow when fresh 2
Pore surface cream to white when fresh 10
2 Occurring on conifers 3
Occurring on hardwoods 6
3 Distributed in cool temperate to boreal zones in East Asia and Europe 4
Distributed in North America 5
4 Basidiospores 6–8 × 4–5.5 µm L. montanus
Basidiospores 5–6.2 × 4.2–5.2 μm L. medogensis
5 Basidiospores 5–7 × 3.8–5 µm; distributed in eastern North America L. huroniensis
Basidiospores 6.5–8 × 4–5 µm; distributed in far western North America L. conifericola
6 Pores 4–5 per mm L. caribensis
Pores 2–4 per mm 7
7 Basidiocarps single, occasionally imbricate but not in large clusters; anamorphic form frequently produced L. versisporus
Basidiocarps imbricate, rarely single; no anamorphic form or rarely produced 8
8 Basidiospores 4.5–5 × 3–4.2 µm L. xinjiangensis
Basidiospores 5–7 × 3–5.5 µm 9
9 Distributed in temperate zones L. sulphureus
Distributed in temperate to tropical zones L. gilbertsonii
10 Basidiocarps arising from soil or surface of roots near the base of living trees L. cincinnatus
Basidiocarp arising from trunks of standing trees or on fallen logs 11
11 Distributed in mountain forests of subtropical zones L. ailaoshanensis
Distributed in cool temperate to boreal zones 12
12 Pileal surface cream to white, pores 3–6 per mm L. zonatus
Pileal surface light orange to reddish-orange, pores 2–4 per mm L. cremeiporus

The main morphological characters, host trees and distribution areas of species in the Laetiporus sulphureus complex.

Species Pileal surface Pore surface Pores Basidiospores Distribution Host References
L. ailaoshanensis orange yellow to reddish orange cream to buff 3–5/mm ovoid to ellipsoid
5.0–6.2 × 4.0–5.0 µm
subtropical areas of south-western China Lithocarpus Song et al. 2014
L. caribensis orange to pale orange lemon yellow 4–5/mm ellipsoid
4.0–4.5 × 2.7–3.6 µm
tropical zones of the Caribbean basin and central America Guarea guidonia, Dacryodes Banik et al. 2012
L. cincinnatus bright salmon orange pale cream 2–4/mm broadly ovoid
4.5–5.5 × 3.5–4.0 µm
throughout the eastern USA except for in the states along the Gulf of Mexico, common in the Great Lakes regions arising from the soil (Quercus) Burdsall and Banik 2001
L. conifericola bright orange to salmon orange lemon yellow to bright creamy yellow 2–4/mm broadly ovoid
6.5–8.0 × 4.0–5.0 µm
western North America from California to Alaska Tsuga, Picea, Abies, Pinus Burdsall and Banik 2001
L. cremeiporus light orange to reddish-orange yellowish-white to cream 2–4/mm ovoid to ellipsoid
5.6–7.0 × 3.9–4.7 µm
cool temperate to boreal areas of East Asia Quercus, Pyrus, Prunus Ota et al. 2009
L. gilbertsonii pale salmon orange or pale pinkish-orange lemon yellow to pale lemon yellow (in West USA) or isabelline to nearly white (in Southeast USA) 2–4/mm broadly ovoid
5.0–6.5 × 3.5–4.5 µm
North America, Central and South America Eucalyptus, Quercus, Prunus Burdsall and Banik 2001, Banik et al. 2012
L. huroniensis bright orange lemon yellow 2–4/mm broadly ovoid
5.0–7.0 × 4.2–5.0 µm
eastern North America and in its Great Lakes areas Tsuga Burdsall and Banik 2001
L. medogensis pinkish-buff to clay-buff buff-yellow 2–4/mm ellipsoid to ovoid
5–6.2 × 4.2–5.2 μm
cool temperate areas of south-western China Abies in the present study
L. montanus light orange to reddish-orange bright sulphurous yellow 1–4/mm pyriform or ovoid to ellipsoid
6.0–8.0 × 4.0–5.5 µm
boreal zones in north-eastern China and in mountain areas of Japan and Central Europe Picea, Larix, Abies Tomšovský and Jankovský 2008, Ota et al. 2009
L. sulphureus bright salmon orange lemon yellow 2–4/mm ovoid to ellipsoid
5.0–6.8 × 4.0–5.0 µm
North America, Europe and South America Acer, Salix, Gleditisa, Quercus, Fraxinus, Castanea, Salix Burdsall and Banik 2001
L. versisporus whitish to sulphur yellow usually yellow, sometimes pale yellow to nearly white 3–6/mm ovoid to short ellipsoid
4.0–6.8 × 3.0–5.5 µm
cool temperate to tropical areas of East Asia Robinia, Castanea, Quercus, Elaeocarpus, Castanopsis Núñez and Ryvarden 2001, Ota et al. 2009
L. xinjiangensis pale-buff to clay-pink cream to light yellow 2–3/mm ellipsoid to ovoid
4.5–5 × 3–4.2 μm
temperate areas of western China Betula, Populus, Salix in the present study
L. zonatus white to cream and buff to clay-buff at base white to cream 2–5/mm ellipsoid to pyriform or drop-shaped
5.8–7.2 × 4.3–5.5 µm
high mountains of temperate areas of south-western China Quercus Song et al. 2014

Acknowledgements

Special thanks are due to Dr. Xiao-Lan He (Soil and Fertilizer Research Institute, Sichuan Academy of Agricultural Sciences, China) and Dr. Xiao-Yong Liu (Institute of Microbiology of the Chinese Academy of Sciences, China) for help in collecting specimens. The research is supported by the Fundamental Research Funds for the Central Universities (No. 2016ZCQ04) and the National Natural Science Foundation of China (Project Nos. 31750001, 31670016).

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