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Phylogenetic and morphological studies in Xylodon (Hymenochaetales, Basidiomycota) with the addition of four new species
expand article infoJanett Riebesehl, Eugene Yurchenko§, Karen K. Nakasone|, Ewald Langer
‡ University of Kassel, Kassel, Germany
§ Polessky State University, Pinsk, Belarus
| U.S. Forest Service, Madison, United States of America
Open Access

Abstract

Xylodon (Hymenochaetales, Basidiomycota) is the largest segregate genus of Hyphodontia s.l. Based on molecular and morphological data, 77 species are accepted in Xylodon to date. Phylogenetic analyses of ITS and 28S sequences, including 38 new ITS and 20 28S sequences of Xylodon species, revealed four species new to science. The new taxa X. exilis, X. filicinus, X. follis and X. pseudolanatus from Taiwan, Nepal, Réunion, Belize, and USA are described and illustrated. In addition, species concepts for Odontia vesiculosa from New Zealand and Xylodon lanatus from U.S.A. are revised and the new name X. vesiculosus is proposed. Phylogenetic analyses of the ITS region placed X. spathulatus, X. bubalinus and X. chinensis in a strongly supported clade and demonstrated that they are conspecific. Palifer and Odontiopsis are synonymised under Xylodon based on morphological and sequence data. The following new combinations are proposed: X. erikssonii, X. gamundiae, X. hjortstamii, X. hyphodontinus, X. septocystidiatus and X. verecundus. Line drawings of X. cystidiatus, X. hyphodontinus, X. lanatus and X. vesiculosus, as well as photographs of X. raduloides basidiomata, are provided. A key to X. lanatus and similar species is presented.

Keywords

Agaricomycetes, corticioid fungi, Schizoporaceae, Schizopora, Odontia ambigua, Xylodon echinatus

Introduction

The corticioid fungal genus Xylodon (Pers.) Gray, based on the generic type X. quercinus (Pers.) Gray, was described in 1801 by Persoon as Sistotrema sect. Xylodon and belongs in the Hymenochaetales (Basidiomycota). Species of Xylodon were usually placed in Hyphodontia J. Erikss. until Hjortstam and Ryvarden (2002, 2009) reorganised Hyphodontia s.l. into different genera based on morphological features.

The most recent generic description of Xylodon was published by Riebesehl and Langer (2017). With few exceptions, the hymenophore in Xylodon is odontioid or poroid with many different cystidia types and basidiospore shapes.

Xylodon spp. are primarily wood decomposers, causing a white-rot of angiosperms and gymnosperms (Eriksson and Ryvarden 1976, Yurchenko and Wu 2014). A few species have been collected on brown-rotten spruce stumps, palms or palm tree inflorescences, bamboo, ferns and on the herbaceous Staehelina dubia L. and Fallopia sachalinensis (F.Schmidt) Ronse Decr. (Burdsall and Nakasone 1981, Langer 1994, Nordén et al. 1999, Kotiranta and Saarenoksa 2000, Boidin and Gilles 2003, Hjortstam et al. 2005, Xiong et al. 2010, Jo et al. 2018). Xylodon has a worldwide distribution, with both cosmopolitan species and species restricted to a limited geographic area.

Palifer Stalpers & P.K.Buchanan (1991), based on Peniophora verecunda G.Cunn. from New Zealand, is another segregate genus of Hyphodontia s.l. recognised by Hjortstam and Ryvarden (2009). It is characterised by encrusted cystidia and remained monotypic until 2007 when three species were transferred to the genus (Hjortstam and Ryvarden 2007a). After a thorough morphological study of Palifer species and related taxa, Gorjón (2012) concluded that Palifer was probably a synonym of Xylodon but did not propose any new combinations. Palifer is represented by only one nuclear ribosomal internal transcribed spacer (ITS) sequence in the public record and phylogenetic analyses showed it to be embedded in Xylodon (Larsson et al. 2006). Riebesehl and Langer (2017), however, declined to synonymise Palifer with Xylodon based on one DNA sequence alone and chose to emphasise its morphological features.

Odontiopsis Hjortstam and Ryvarden (1980) is based on the type species O. hyphodontina Hjortstam & Ryvarden from Tanzania. It is characterised by an odontioid hymenium, encrusted hyphae projecting from the aculei, stout basidia and globose to subglobose basidiospores. Hjortstam and Ryvarden (1980) mentioned hyphal and basidial similarities with Schizopora and Hyphodontia.

In this study, we conducted an in-depth phylogenetic study of 36 Xylodon species represented by 96 strains or collections, including 58 new ITS and large subunit (28S) ribosomal DNA sequences. Phylogenetic analyses of the ITS and 28S sequence data uncovered four new taxa, X. exilis, X. filicinus, X. follis and X. pseudolanatus, that are described and illustrated. In addition, the species complex of X. spathulatus was identified and resulted in the synonymisation of two taxa. The genera Palifer and Odontiopsis are re-evaluated and placed in synonymy with Xylodon, resulting in a number of new combinations. Morphological studies in Xylodon lanatus and Odontia vesiculosa were conducted and a key to morphologically similar species is provided. Line drawings of X. cystidiatus, X. hyphodontinus and X. vesiculosus are presented and X. vesiculosus is described.

Methods

Molecular study

Pieces of dried basidiomata served as material for DNA extractions with the E.Z.N.A.® Fungal DNA Mini Kit (Omega Bio-Tek, VWR, USA). Two nuclear ribosomal DNA markers were used in this study: the ITS region and the D1-D2 domains of 28S. The ITS region includes the internal transcribed spacers 1 and 2 as well as the intercalary 5.8S rRNA gene. For amplification of ITS, different combinations of the following primers were used: ITS1-F (Gardes and Bruns 1993), ITS1, ITS2, ITS3, ITS4, ITS5 (White et al. 1990) and ALR0 (Collopy et al. 2001). The last one was modified in one position (Riebesehl and Langer 2017). NL1, NL4 (O’Donnell 1993), LR0R (Bunyard et al. 1996) and LR5 (Vilgalys and Hester 1990) were used, also in different combinations, for the amplifications of the D1-D2 domains of 28S. PCR products were purified with innuPREP PCRpure Kit (Analytik Jena, Berlin, Germany) and the DNA sequencing was implemented by Eurofins Genomics (Ebersberg, Germany).

Newly generated sequences were edited with MEGA7 (Kumar et al. 2016). Their quality was checked following the five guidelines by Nilsson et al. (2012) and they were deposited in NCBI GenBank (Benson et al. 2018; Tab. 1). Other sequences used in this study were downloaded from the same database. Phellinus gabonensis Decock & Yombiyeni (Hymenochaetales) was chosen as the outgroup for rooting the phylograms. The two different alignments were calculated with MAFFT v.7 (Katoh and Standley 2013), using the L-INS-i algorithm for ITS and G-INS-i for 28S. Minimum Evolution (ME) and Bayesian inference (BI) trees were calculated for both datasets. The ME phylograms were computed with MEGA7, using the Tamura-Nei model (Tamura and Nei 1993) including 1000 bootstrap (BS) replications, partial deletion of gapped positions with 95% site coverage cut-off and other default settings. The BI phylograms were constructed with MrBayes 3.2.6 (Ronquist and Huelsenbeck 2003), using DNA substitution models estimated by MrModeltest 2.4 (Nylander 2004) with 10 million generations and one tree saved for every 1000 generations; other parameters used default settings. A partitioned analysis was done for the ITS alignment with independent DNA substitution models and parameter values for ITS1, 5.8S and ITS2. MEGA7 and FigTree 1.4.2 (Rambaut 2012) were used for processing the phylograms.

Morphological study

The studied specimens are deposited in herbaria CFMR, FR, KAS, LIP, MSK, and TUB (acronyms follow Index Herbariorum, http://sweetgum.nybg.org/science/ih). Morphological descriptions and figures employed dried basidiomata. Preparations in 3% potassium hydroxide (KOH) aqueous solution were used for microscopic measurements and most drawings. Crystalline deposits on hyphae were additionally examined in Melzer’s reagent (Mz) and tap water. Amyloid and dextrinoid reactions of basidiospores were tested with Mz. Spore wall cyanophily was determined in Cotton Blue-Lactophenol solution (CBL). The following abbreviations are used to describe arithmetic averages for 30 basidiospores, randomly selected in squash preparations of one specimen: L – spore length, W – spore width, Q = length/width ratio.

Results

Phylogeny

The aligned ITS data matrix consisted of 92 taxa and 847 positions. The partial deletion of gapped positions resulted in 463 positions that were used in the ME phylogenetic analysis. The data matrix was partitioned as follows: ITS1 = positions 1–373, 5.8S rRNA gene = 374–541 and ITS2 = 542–847. The GTR + G model was used as DNA substitution model for ITS1 and ITS2 and SYM + I for 5.8S in the BI analysis. The aligned data matrix of the D1-D2 domains of 28S rRNA gene consisted of 47 taxa and 634 positions; 532 positions were used in the ME analysis. The GTR + I + G model was chosen as the DNA substitution model for the BI analysis. A high degree of agreement was observed between the ME and BI trees; therefore, the ME phylogram with BS and integrated posterior probability (PP) values from the BI phylogram are presented in Figures 1, 2. The sum of branch lengths in the resulting ME phylograms was 3017 for ITS (Fig. 1) and 1009 for 28S (Fig. 2). Multiple sequence alignments and trees are deposited in TreeBASE (http://purl.org/phylo/treebase/phylows/study/TB2:S23512).

Figure 1. 

ITS-based Minimum Evolution phylogram for Xylodon and allied species. Bootstrap values >50 are shown next to the branches. The second number, if present, represents posterior probabilities received from BI analysis. Scale bar indicates estimated number of substitutions per site. Sequences generated in this study are shown in bold. Voucher numbers and species names are indicated in Table 1.

The ITS phylogram (Fig. 1) shows a number of clades with low BS support which is well-documented for Xylodon (see Chen et al. 2018, Riebesehl and Langer 2017). Figure 1 includes 83 sequences of Xylodon specimens or strains of which 38 were generated in this study. No significant distances were observed amongst sequences of X. niemelaei, X. rhizomorphus, and X. reticulatus nor amongst sequences of X. spathulatus, X. chinensis, and X. bubalinus. The strong BS (99 and 97) and PP (1) values of these two clades indicate that the taxa within each clade may be conspecific. Seven collections of X. raduloides form two distinct subclades (96 and 98 BS). Similarly, four collections of X. flaviporus formed two subclades (99 and 93 BS). The newly generated ITS sequences show that X. cystidiatus, X. hyphodontinus, X. serpentiformis and X. subclavatus form distinct lineages in Xylodon. The four new species introduced herein form distinct lineages as well. Xylodon pseudolanatus and X. exilis are sister groups with 5.9% differences between their ITS sequences (X. pseudolanatus: FP-150922 and X. exilis: TUB-FO 42565). They cluster in a well-supported clade (99 BS), within a weakly supported lineage that includes X. follis. The closest relative of X. filicinus is X. hastifer; they form a clade (93 BS) that is sister to X. hyphodontinus s.l.

The 28S phylogram (Fig. 2) includes 39 sequences of Xylodon of which 20 were generated here. Notable new 28S sequences include X. australis, X. hyphodontinus, X. serpentiformis, the four new species described herein, and furthermore Hyphodontia borbonica. As the 28S phylogram features several lineages with low BS support, the clades between the 28S and ITS trees are not identical throughout. Although clearly resolved with ITS sequences, the 28S gene analyses were not able to resolve the closely related X. raduloides and X. subtropicus. Some clades that were well supported with ITS sequences were also well supported in the 28S phylogram, for example, the X. niemelaei and X. reticulatus (100 BS) and the X. chinensis and X. spathulatus (99 BS) clades.

Figure 2. 

28S-based Minimum Evolution phylogram for Xylodon and allied species. Bootstrap values >50 are shown next to the branches. The second number, if present, represents posterior probabilities received from BI analysis. Scale bar indicates estimated number of substitutions per site. Sequences generated in this study are shown in bold. Voucher numbers and species names are indicated in Table 1.

List of accepted species in Xylodon with some closely related species from other genera, including specimens used in the phylogenetic study. Newly generated sequences are shown in bold. Xylodon species without available ITS or 28S sequences are marked with ‘not available’ (n.a.); these have to date not been studied using ribosomal sequence data.

Species Specimen voucher GenBank accession number Reference Country
ITS 28S
Hastodontia hastata (Litsch.) Hjortstam & Ryvarden KAS-GEL3124 DQ340311 unpublished Sweden
EL47/99 (GB) DQ873620 Larsson et al. 2006 Sweden
Hyphodontia borbonica Riebesehl, Langer & Barniske FR-0219441, Holotype KR349240 Riebesehl et al. 2015 Réunion
MH884915 This study
H. pallidula (Bres.) J.Erikss. KAS-GEL2097 DQ340317 DQ340372 unpublished Germany
Kneiffiella barba-jovis (Bull.) P.Karst. KHL 11730 (GB) DQ873609 DQ873610 Larsson et al. 2006 Sweden
K. palmae Rick ex Hjortstam & Ryvarden FR7 KP689185 Wang et al. 2016 China
KAS-GEL3456 DQ340369 unpublished Taiwan
Lagarobasidium calongei M.Dueñas, Tellería, Melo & M.P.Martín MA-Fungi 73256 NR119737 n.a. Dueñas et al. 2009 Azore Islands
Lyomyces crustosus (Pers.) P.Karst. TASM YG-G39 MF382993 Gafforov et al. 2017 Uzbekistan
KAS-GEL2325 DQ340354 unpublished Germany
L. sambuci (Pers.) P.Karst. KAS-JR7 KY800402 KY795966 Yurchenko et al. 2017 Germany
Phellinus gabonensis Decock & Yombiyeni MUCL 52025 HM635715 HM635690 Yombiyeni et al. 2011 Gabon
Xylodon adhaerisporus (Langer) Hjortstam & Ryvarden n.a. n.a.
X. anmashanensis (Yurchenko, H.X.Xiong & Sheng H.Wu) Riebesehl, Yurchenko & Langer n.a. n.a.
X. apacheriensis (Gilb. & Canf.) Hjortstam & Ryvarden Canfield 180, Holotype KY081800 n.a. Riebesehl and Langer 2017 USA, Arizona
X. archeri (Berk.) Kuntze n.a. n.a.
X. asperus (Fr.) Hjortstam & Ryvarden UC2023169 KP814365 Rosenthal et al. 2017 USA, Montana
KHL8530 (GB) AY586675 Larsson et al. 2004 Sweden
X. astrocystidiatus (Yurchenko & Sheng H.Wu) Riebesehl, Yurchenko & Langer Wu 9211-71 JN129972 JN129973 Yurchenko and Wu 2014 Taiwan
X. australis (Berk.) Hjortstam & Ryvarden CIEFAP-11041 (CFMR) n.a. MH884895 This study Argentina
X. bisporus (Boidin & Gilles) Hjortstam & Ryvarden n.a. n.a.
X. borealis (Kotir. & Saaren.) Hjortstam & Ryvarden UC2022850 KP814307 Rosenthal et al. 2017 USA, Connecticut
JS26064 AY586677 Larsson et al. 2004 Norway
X. bresinskyi (Langer) Hjortstam & Ryvarden n.a. n.a.
X. brevisetus (P. Karst.) Hjortstam & Ryvarden KHL 12386 (GB) DQ873612 DQ873612 Larsson et al. 2006 Sweden
X. bubalinus (Min Wang, Yuan Y. Chen & B.K. Cui) C.C. Chen & Sheng CLZhao 184 MG231628 n.a. unpublished China
Cui 6834 KY290981 Wang and Chen 2017 China
Cui 12887 KY290982 Wang and Chen 2017 China
Cui 12888, Holotype KY290983 Wang and Chen 2017 China
X. candidissimus (Berk. & M.A.Curtis) Hjortstam & Ryvarden n.a. n.a.
X. capitatus (G.Cunn.) Hjortstam & Ryvarden n.a. n.a.
X. chinensis (C.C.Chen & Sheng H.Wu) C.C.Chen & Sheng H.Wu Wu 1307-42 KX857802 Chen et al. 2017 China
Wu 1407-105, Holotype KX857804 KX857811 Chen et al. 2017 China
X. crassihyphus (Douanla-Meli) Riebesehl & Langer n.a. n.a.
X. crassisporus (Gresl. & Rajchenb.) Hjortstam & Ryvarden n.a. n.a.
X. crustosoglobosus (Hallenb. & Hjortstam) Hjortstam & Ryvarden n.a. n.a.
X. cystidiatus (A.David & Rajchenb.) Riebesehl & Langer FR-0249200 MH880195 MH884896 This study Réunion
X. detriticus (Bourdot) Tura, Zmitr., Wasser & Spirin UC2023108 KP814412 n.a. Rosenthal et al. 2017 USA, Michigan
X. echinatus (Yurchenko & Sheng H.Wu) Riebesehl, Yurchenko & Langer n.a. n.a.
X. erikssonii (M.Galán & J.E.Wright) Riebesehl & Langer n.a. n.a.
X. exilis Yurchenko, Riebesehl & Langer MSK-F 7381 MH880196 This study Taiwan
MSK-F 7431 MH884897 This study Taiwan
TUB-FO 42450 MH880197 This study Taiwan
TUB-FO 42565, Holotype MH880198 MH884898 This study Taiwan
X. filicinus Yurchenko & Riebesehl MSK-F 12869, Holotype MH880199 MH884899 This study Taiwan
MSK-F 12870 MH880200 MH884900 This study Taiwan
X. fimbriatus (Sheng H.Wu) Hjortstam & Ryvarden n.a. n.a.
X. flaviporus (Berk. & M.A.Curtis ex Cooke) Riebesehl & Langer FCUG 1053 AF145575 Paulus et al. 2000 Romania
FR-0249797 MH880201 MH884901 This study Réunion
KAS-GEL3462 MH880202 This study Taiwan
KAS-GEL5047 MH880203 This study Réunion
KUC20130808-17 KJ668314 Jang et al. 2016 South Korea
X. follis Riebesehl, Yurchenko & Langer FR-0249814, Holotype MH880204 MH884902 This study Réunion
X. gamundiae (Gresl. & Rajchenb.) Riebesehl & Langer n.a. n.a.
X. gracilis (Hjortstam & Ryvarden) Hjortstam & Ryvarden n.a. n.a.
X. hallenbergii (Sheng H.Wu) Hjortstam & Ryvarden n.a. n.a.
X. hastifer (Hjortstam & Ryvarden) Hjortstam & Ryvarden Ryvarden 19767, Holotype KY081801 n.a. Riebesehl and Langer 2017 Argentina
X. heterocystidiatus (H.X.Xiong, Y.C.Dai & Sheng H.Wu) Riebesehl, Yurchenko & Langer Wu 9209-27 JX175045 Yurchenko and Wu 2014 Taiwan
KX857821 Chen et al. 2017
X. hjortstamii (Gresl. & Rajchenb.) Riebesehl & Langer n.a. n.a.
X. hyphodontinus (Hjortstam & Ryvarden) Riebesehl, Yurchenko & G.Gruhn KAS-GEL9222 MH880205 MH884903 This study Kenya
LIP GG-GUY13-044 MH880206 MH884904 This study French Guyana
LIP GG-MAR12-238 MH880207 MH884905 This study Martinique
LIP GG-MAR15-127 MH880208 MH884906 This study Martinique
X. knysnanus (Van der Byl) Hjortstam & Ryvarden n.a. n.a.
X. lanatus (Burds. & Nakasone) Hjortstam & Ryvarden n.a. n.a.
X. lenis Hjortstam & Ryvarden Wu0808-32 KX857820 Chen et al. 2017 Taiwan
Wu890714-3, Holotype KY081802 Riebesehl and Langer 2017 Taiwan
X. lutescens (Hjortstam & Ryvarden) Hjortstam & Ryvarden n.a. n.a.
X. mollissimus (L.W.Zhou) C.C.Chen & Sheng H.Wu LWZ20160318-3 KY007517 n.a. Kan et al. 2017 China
X. mussooriensis Samita, Sanyal & Dhingra n.a. n.a.
X. nespori (Bres.) Hjortstam & Ryvarden KAS-GEL3158 DQ340346 unpublished Sweden
KAS-JR14 MH880210 This study Germany
KUC20161012-50 MF774797 unpublished South Korea
X. nesporina (Hallenb. & Hjortstam) Hjortstam & Ryvarden n.a. n.a.
X. niemelaei (Sheng H.Wu) Hjortstam & Ryvarden Dai 15358 KT989973 Chen et al. 2016 China
FR-0219860 MH880211 This study Réunion
FR-0249174 MH880212 This study Réunion
FR-0249178 MH884907 This study Réunion
FR-0249225 MH880213 This study Réunion
FR-0249289 MH880214 This study Réunion
FR-0249744 MH880215 This study Réunion
FR-0249811 MH880216 This study Réunion
FR-0249846 MH880217 This study Réunion
GC 1508-146 KX857798 Chen et al. 2017 Taiwan
KAS-GEL4904 MH880218 This study Réunion
KAS-GEL4998 EU583422 unpublished Réunion
Wu1010-62 KX857817 Chen et al. 2017 Taiwan
X. nongravis (Lloyd) C.C.Chen & Sheng H.Wu GC1412-22 KX857801 KX857818 Chen et al. 2017 Taiwan
X. nothofagi (G.Cunn.) Hjortstam & Ryvarden PDD:91630 GQ411524 Fukami et al. 2010 New Zealand
X. nudisetus (Warcup & P.H.B.Talbot) Hjortstam & Ryvarden n.a. n.a.
X. ovisporus (Corner) Riebesehl & Langer ICMP 13830 AF145584 Paulus et al. 2000 New Zealand
KAS-GEL3493 EU583421 unpublished Taiwan
KUC20130725-29 KJ668365 Jang et al. 2016 South Korea
X. papillosus (Fr.) Riebesehl, Yurchenko & Langer n.a. n.a.
X. paradoxus (Schrad.) Chevall. FCUG 2425 AF145571 Paulus et al. 2000 Russia
KAS-GEL2511 AF518647 Hibbett and Binder 2002 Germany
KAS-JR06 MH880219 This study Germany
KAS-JR28 MH884908 This study Austria
X. pelliculae (H.Furuk.) Riebesehl, Yurchenko & Langer n.a. n.a.
X. poroideoefibulatus (Sheng H.Wu) Hjortstam & Ryvarden n.a. n.a.
X. pruniaceus (Hjortstam & Ryvarden) Hjortstam & Ryvarden n.a. n.a.
X. pseudolanatus Nakasone, Yurchenko & Riebesehl FP-150922 (CFMR), Holotype MH880220 MH884909 This study Belize
X. pseudotropicus (C.L.Zhao, B.K.Cui & Y.C.Dai) Riebesehl, Yurchenko & Langer Dai 10768 KF917543 n.a. Zhao et al. 2014 China
X. quercinus (Pers.) Gray Otto Miettinen 15050,1 (H 6013352) KT361632 Ariyawansa et al. 2015 Finland
KHL11076 (GB) KT361633 AY586678 Larsson et al. 2004 Sweden
X. raduloides (Pers.) Riebesehl & Langer ICMP 13833 AF145580 Paulus et al. 2000 Australia
KAS-JR 02 MH880221 This study Germany
KAS-JR 03 MH880222 This study Germany
KAS-JR 09 MH880223 This study Germany
X. raduloides (Pers.) Riebesehl & Langer KAS-JR 10 MH880224 This study Germany
KAS-JR 26 MH880225 MH884910 This study Germany
LR 18813 MH880226 MH884911 This study Australia
X. ramicida Spirin & Miettinen Viacheslav Spirin 7664 (H), Holotype KT361634 n.a. Ariyawansa et al. 2015 Russia
X. reticulatus (C.C.Chen & Sheng H.Wu) C.C.Chen & Sheng H.Wu GC1512-1 KX857808 KX857813 Chen et al. 2017 Taiwan
KUC20160721B-26 MF774798 Kwon et al. 2018 South Korea
Wu1109-178, Holotype KX857805 Chen et al. 2017 Taiwan
X. rhizomorphus (C.L.Zhao, B.K.Cui & Y.C.Dai) Riebesehl, Yurchenko & Langer Dai 12354 KF917544 n.a. Zhao et al. 2014 China
Dai 12367, Holotype KF917545 Zhao et al. 2014 China
Dai 12389 KF917546 Zhao et al. 2014 China
X. rickii (Hjortstam & Ryvarden) K.H. Larss. n.a. n.a.
X. rimosissimus (Peck) Hjortstam & Ryvarden Ryberg 021031 (GB) DQ873627 DQ873628 Larsson et al. 2006 Sweden
X. rudis (Hjortstam & Ryvarden) Hjortstam & Ryvarden n.a. n.a.
X. septocystidiatus (H.X.Xiong, Y.C.Dai & Sheng H.Wu) Riebesehl & Langer n.a. n.a.
X. serpentiformis (Langer) Hjortstam & Ryvarden KAS-GEL3668 MH880227 This study Taiwan
TUB-FO 40675 MH880228 This study Taiwan
TUB-FO 40985 MH884912 This study Taiwan
TUB-FO 42688 MH880229 MH884913 This study Taiwan
X. sp. 1 Dai 15321 KT989969 n.a. Chen et al. 2016 China
X. spathulatus (Schrad.) Kuntze KAS-GEL2690 KY081803 Riebesehl and Langer 2017 Germany
KAS-MMS7224 MH880230 This study Czech Republic
KHL7085 (GB) KY081804 Riebesehl and Langer 2017 Sweden
MSK-F 12931 MH880231 MH884914 This study Russia
X. subclavatus (Yurchenko, H.X.Xiong & Sheng H.Wu) Riebesehl, Yurchenko & Langer TUB-FO 42167 MH880232 n.a. This study Taiwan
X. subflaviporus C.C.Chen & Sheng H.Wu KAS-GEL3466 MH880233 This study Taiwan
Wu 0809-76 KX857803 KX857815 Chen et al. 2017 China
X. subglobosus Samita, Sanyal & Dhingra n.a. n.a.
X. submucronatus (Hjortstam & Renvall) Hjortstam & Ryvarden n.a. n.a.
X. subscopinellus (G.Cunn.) Hjortstam & Ryvarden n.a. n.a.
X. subtropicus (C.C.Chen & Sheng H.Wu) C.C.Chen & Sheng H.Wu Wu 1508-2 KX857806 KX857812 Chen et al. 2017 China
Wu 9806-105, Holotype KX857807 KX857809 Chen et al. 2017 Vietnam
X. syringae (Langer) Hjortstam & Ryvarden n.a. n.a.
X. taiwanianus (Sheng H.Wu) Hjortstam & Ryvarden n.a. n.a.
X. tenellus Hjortstam & Ryvarden n.a. n.a.
X. tenuicystidius (Hjortstam & Ryvarden) Hjortstam & Ryvarden n.a. n.a.
X. trametoides (Núñez) Riebesehl & Langer n.a. n.a.
X. tuberculatus (Kotir. & Saaren.) Hjortstam & Ryvarden n.a. n.a.
X. verecundus (G.Cunn.) Yurchenko & Riebesehl KHL 12261 (GB) DQ873642 n.a. Larsson et al. 2006 USA
X. vesiculosus Yurchenko, Nakasone & Riebesehl n.a. n.a.

Morphology

Xylodon exilis Yurchenko, Riebesehl & Langer, sp. nov.

MycoBank No: MB827462
Figs 3a, 4

Holotype

TAIWAN, Nantou county, south from Sun-Moon Lake, near Hua Lien, Lien-Hwa-Chi, 700 m a.s.l., on fallen angiosperm twig, leg. E. Langer, G. Langer, F. Oberwinkler, 10 Jul 1990 (TUB-FO 42565; isotypes in KAS and MSK).

Description

Basidiomata effused, 1–5 cm in extent, membranaceous, discontinuous at the periphery. Hymenial surface minutely odontioid, cream-coloured, between aculei 50–130 μm thick. Aculei peg-like, conical or subcylindrical, entire or slightly penicillate apically, 35–70 μm long, 15–50(–70) μm diam., 8–14/mm. Margin abrupt or somewhat thinning out. Hyphal system monomitic, hyphae colourless, with clamps at all primary septa. Subicular hyphae forming a loose tissue, rarely branched, 3–4(–4.5) μm wide, with slightly thick to thick walls (0.5–1.2 μm thick), with scattered adventitious septa, smooth. Subhymenial hyphae in a dense tissue, richly branched, 2–3 μm wide, thin-walled, smooth or slightly encrusted. Capitate cystidia enclosed, 18–22 × 5.5–8 μm, sometimes with an adventitious septum in stem, thin- to slightly thick-walled. Projecting hyphae in aculei flexuous, apically obtuse, 90–130 μm long, 3–4 μm wide, originating from thick-walled subicular hyphae, with simple and clamped septa, often constricted at septa, walls thickened at base then gradually thinning toward apex, moderately encrusted. Basidioles clavate or bowling pin-shaped, 10–20 × 4.5–5.5 μm. Basidia narrowly utriform, 20–25 × 4–5(–5.5) μm, thin-walled, smooth, with four sterigmata 2–4 × 0.3 μm. Spores narrowly ellipsoid, 5.5–6 × 2.5–3 μm, holotype L = 5.8 µm, W = 2.8 µm, Q = (1.6–)1.8–2.2, colourless, smooth, slightly thick-walled, negative in Mz, acyanophilous, with minute apiculus.

Figure 3. 

Basidiomata of Xylodon spp. A X. exilis (TUB-FO 42565, holotype) B X. filicinus (MSK-F 12369, holotype) C X. follis (FR-0249814, holotype) D X. pseudolanatus (FP-150922, holotype) E X. pseudolanatus (HHB-6925, paratype) F X. vesiculosus (PDD-18112, isotype) G X. lanatus (CFMR HHB-8925, holotype). Scale bars: 1 mm.

Distribution and ecology

The species is known from Taiwan and Nepal. It grows on dead wood of angiosperms, with a preference for small branches and twigs.

Etymology

from Latin exilis – thin, fine, refers to the small and narrow aculei.

Figure 4. 

Micromorphology of Xylodon exilis (TUB-FO 42565, holotype): A, B vertical sections through basidioma C subicular hyphae D portion of hymenium and subhymenium E projecting aculeal hyphae in Mz F projecting aculeal hyphae in 3% KOH G capitate cystidia H basidioles J basidia K basidiospores. Scale bars: 100 μm (A); 20 μm (B); 10 μm (C–J); 5 μm (K).

Additional specimens examined

TAIWAN, Nantou Co., west from Sun-Moon Lake, near Hua Lien, on dead wood, leg. E. Langer, G. Langer, F. Oberwinkler, 26 Mar 1989 (TUB-FO 40734; dupl. in KAS); south from Sun-Moon Lake, near Hua Lien, on fallen angiosperm twig, leg. E. Langer, G. Langer, F. Oberwinkler, 9 Jul 1990 (TUB-FO 42450; dupl. in KAS and MSK); Taichung Co., Shinshe, on fallen angiosperm twig, leg. E. Yurchenko, 2 Apr 2011 (MSK-F 12912); ibid., on fallen liana stem, leg. E. Yurchenko, 2 Apr 2011 (MSK-F 12913); ibid., on fallen angiosperm twig, leg. E. Yurchenko, 5 Jun 2011 (MSK-F 12914); Taipei Co., Wulai, Neidong Recreation Area, on fallen angiosperm twig, leg. E. Yurchenko, 23 Jun 2011 (MSK-F 7381; dupl. in KAS and LE); Miaoli Co., Sanyi, on fallen angiosperm branch, leg. E. Yurchenko, 3 Jul 2011 (MSK-F 7431); ibid., on fallen angiosperm branch, leg. E. Yurchenko, 19 Jul 2011 (MSK-F 7430). NEPAL: Gandaki Prov., Kuldi, Anapurna Trek, leg. L. Ryvarden, 7 Nov 1979 (O-LR 18918/B, dupl. in KAS).

Remarks

The species concept of X. lanatus is revised and restricted to specimens with a well-developed woolly subiculum. The distinctive characters of X. exilis are the minutely odontioid basidiomata with peg-like aculei composed of flexuous, encrusted, septate projecting hyphae that are constricted at the septa, embedded capitate cystidia and narrowly ellipsoid spores with slightly thickened walls. Earlier specimens of X. exilis from Taiwan (e.g. Langer 1994, p. 143 for illustration) and Nepal (Hjortstam and Ryvarden 1984) were originally identified as X. lanatus. Hyphae and spores of this species were also depicted by Yurchenko et al. (2013) under the name X. lanatus. These two species and other morphologically similar taxa are compared in the Discussion section below; a key is also presented.

Xylodon filicinus Yurchenko & Riebesehl, sp. nov.

MycoBank No: MB827463
Figs 3b, 5

Holotype

TAIWAN, Nantou Co., Xitou (Shitou) Forest Recreation Area, W slope of Phoenix Mt. Range, 1470 m a.s.l., 23°40'N, 120°48'E, old-growth sparse broadleaf forest, on dead detached rachis of Cyathea sp., leg. E. Yurchenko, 31 Jul 2011 (field No. 38; MSK-F 12869; isotype in KAS).

Description

Basidiomata effused, white, 2–4 cm in extent, farinaceous or pruinose, very loose or discontinuous, odontioid, 30–55 μm thick between aculei. Margin thinning out. Aculei conical or subcylindrical, 40–80 μm long, 15–45 μm diam., peg-like, of loose texture, 8–14/mm. Hyphal system monomitic, hyphae colourless, clamped at all septa. Subicular hyphae in a loose tissue, rarely branched, 2–3 μm diam., thin- or slightly thick-walled, loosely encrusted, under the subhymenium with inflations 5–6.5 μm wide. The largest crystals in subiculum 6–8 μm across, aggregated in clusters 15–18 μm diam. Subhymenial hyphae moderately branched, partly short-celled and slightly inflated, 2–3.5(–4) μm diam., lightly encrusted. Projecting hyphae in aculei richly encrusted, 20–45 × 5–7 μm in encrusted part, with clamped and simple septa, basally thick-walled, then becoming thin-walled, obtuse, sometimes subacute at apex. Cystidia in hymenium thin-walled, lightly encrusted, of three types: (1) subcylindrical, often slightly tapered to apex, numerous, 20–35 × 4.5–5.5 μm; (2) capitate, rare, 26–32 μm long, 3–5 μm wide at base, 2.5–3 μm wide at apex; (3) hyphoid to narrowly ventricose, about 30 × 4.5 μm. Basidioles ellipsoid, ovoid, clavate, 7.5–18 × 4.5–7.5 μm, more or less encrusted. Basidia utriform, (14–)16–20 × (3.5–)4.5–5.5 μm, thin-walled, smooth or sparsely encrusted, with four sterigmata 2–6.5 × 1–1.5 μm. Spores globose to subglobose, 4–5(–5.5) × (3.7–)4–4.5 μm, holotype L = 4.7 µm, W = 4.1 µm, Q = 1.1–1.2, thin-walled, often with one large oil-like globule, negative in Mz, weakly cyanophilous, with minute apiculus.

Figure 5. 

Micromorphology of Xylodon filicinus (MSK-F 12369, holotype): A vertical section through basidioma B subicular hyphae C inflations on hyphae in lower subhymenium D crystals from subiculum E portions of hymenium and subhymenium F bundle of encrusted projecting hyphae G separate projecting hyphae H subcylindrical cystidia J capitate cystidia K hyphoid cystidium L basidioles M basidia N basidiospores. Scale bars: 100 μm (A); 10 μm (B–M); 5 μm (N).

Distribution and ecology

From the lower mountainous belt in Taiwan, on dead fern rachises.

Etymology

from Latin filix ‒ fern, refers to the occurrence on dead fern rachises.

Additional specimen examined. TAIWAN, the same locality and the same substrate as holotype, leg. E. Yurchenko, 31 Jul 2011 (field No. 18; MSK-F 12870; dup. in KAS).

Remarks

The distinctive features of this species are the pruinose, minutely odontioid basidiomata, fascicles of richly encrusted projecting hyphae in aculei and the three types of cystidia. Xylodon filicinus is morphologically similar to X. hyphodontinus, which differs in having projecting hyphae in the aculei that are straighter with more septa, a denser subhymenium composed of short-celled hyphae, short, ventricose cystidioles and spore walls that are slightly thickened at maturity (see Fig. 6).

Figure 6. 

Micromorphology of Xylodon hyphodontinus. LIP GG-MAR 15-127: A vertical section through basidioma B subicular hyphae C excerpt of tramal hyphae to hymenium and projecting hyphae D bundle of encrusted aculeal hyphae E encrustation on projecting hypha in water F encrustation on projecting hyphae in 3% KOH G naked projecting hyphal end H variously shaped hyphal ends J capitate cystidia K portion of hymenium and subhymenium L basidioles and cystidioles M basidiospores. LIP GG-MAR 12-238: N basidia. Scale bars: 100 μm (A); 10 μm (B–L, N); 5 μm (M).

Xylodon follis Riebesehl, Yurchenko & Langer, sp. nov.

MycoBank No: MB827464
Figs 3c, 7

Holotype

REUNION, Forêt Notre Dame de la Paix, Sentier botanique, 21°15.8'S, 55°36.1'E, 1720 m a.s.l., on angiosperm wood, leg. J. Riebesehl, M. Schröder, M.M. Striegel, 12 Mar 2015 (FR-0249814; isotypes in KAS (as L1040) and MSK).

Description

Basidiomata effused, cream-coloured, about 1–5 cm in extent, soft-membranaceous, continuous, finely aculeate, between aculei 50–200 μm thick; aculei narrowly conical or nearly cylindrical, 80–170 × 20–40(–60) μm, 10–12/mm, fragile, slightly fimbriate at apices, sterile. Margin abrupt. Hyphal system monomitic; hyphae clamped and simple septate, colourless, (1–)2–3.5 μm diam. Subiculum little differentiated, composed of thin- to slightly thick-walled hyphae. Hyphae in aculeal trama mostly parallel, thin- to thick-walled (walls up to 1 μm thick), projecting through aculeal apices and loosely encrusted with crystals about 1–3 μm long in KOH. Subhymenium thickening; subhymenial hyphae moderately branched, thin-walled, smooth. Capitate cystidia numerous, projecting and immersed, in subhymenium, hymenium and aculei, 17–30(–40) × 4.5–9 μm, with 1–2 adventitious septa in stalk, apical cap encased with resinous encrustation 6–12 μm wide, easily dissolving in KOH and Mz, unchanged in CBL. Hyphidial elements common in hymenium, 17–27 × 2.3–3.2 μm. Basidioles pyriform or ellipsoid, 17–28 × 8–12 μm, with granular contents, smooth or slightly encrusted. Basidia utriform or suburniform, thin-walled, smooth, 32–37 × 9–10 μm, with 4 sterigmata 4–6.5 × 1.3–2.3 μm. Spores globose to subglobose, colourless, with homogeneous or granular contents, smooth, inamyloid, indextrinoid, cyanophilous, thin-walled, (7.5–)8–9.5(–10) × 7–8.5 μm, holotype L = 8.6 μm, W = 7.6 μm, Q = 1.0–1.2, outer wall layer sometimes swelling in KOH and CBL, with rounded-triangular apiculus.

Figure 7. 

Micromorphology of Xylodon follis (FR-0249814, holotype): A vertical section through basidioma B subicular hyphae C vertical section through aculeus D lower and apical part of aculeal hyphae with adventitious septa E encrusted aculeal hyphae in water F partially dissolved crystals on aculeal hyphae in 3% KOH G capitate cystidia H portion of hymenium J vesicular basidiole K capitate encrusted cystidia and their detached resinous caps L basidia and basidiospores M basidiospores in 3% KOH N basidiospores in water O basidiospores in CBL. Scale bars: 100 μm (A); 10 μm (B–N).

Distribution and ecology

The species is so far known from Réunion (Mascarene Archipelago) and inhabits dead wood.

Etymology

from Latin follis ‒ bag or bubble, referring to shape of the spores, basidioles and capitate cystidia found in this species.

Additional specimen examined. REUNION, Forêt de Bébour, 1328 m asl., leg. E. Langer, G. Langer, E. Hennen, 20 Mar 1998 (KAS-GEL 4951; dupl. in MSK).

Remarks

This taxon differs from other Xylodon species by its unusually large basidia, large globose basidiospores with walls that swell in KOH and CBL and numerous simple septa as well as clamps on the hyphae. The swelling of spore walls was observed in some spores; spores were unaffected in water mounts. The hymenium has a granular appearance visible under 100× magnification because of the resinous cap developed on the capitate cystidia. The resinous caps are observed only in CBL and are easily detaching in squash preparations. Intermediate forms in morphology of hyphidia to capitate cystidia and of capitate cystidia to pyriform basidioles were frequently observed.

Xylodon pseudolanatus Nakasone, Yurchenko & Riebesehl, sp. nov.

MycoBank No: MB827465
Figs 3d, 8

Holotype

BELIZE: Cayo District, Mountain Pine Ridge, on corticated hardwood branch, leg. K.K. Nakasone, 24 Nov 2001 (CFMR FP-150922; isotypes in KAS and MSK; ex-type culture CFMR FP-150922-sp; ex-type ITS sequence MH880220; ex-type 28S sequence MH884909).

Description

Basidiomata effused, membranaceous, cream-coloured, 1–6 cm in extent, odontioid with conical aculei 50–120 μm long and 25–65 μm diam. at base, 8–14 aculei/mm. Subiculum between aculei very loose, minutely porulose, 100–150 μm thick. Margin pale cream-coloured, abrupt or diffuse, up to 2 μm wide. Hyphal system monomitic, hyphae clamped at all primary septa, colourless. Subicular hyphae little branched, mostly thick-walled, 2.5–4 μm diam., smooth or scarcely encrusted. Subhymenial hyphae richly branched, thin-walled, 2–3.5(–4.5) μm diam., smooth or slightly encrusted. Aculei consisting mostly of projecting hyphae. Projecting hyphae moderately flexuous, (3–)3.5–5 μm diam., slightly thick-walled, loosely encrusted, clamped at septa. Capitate cystidial elements found mostly in subhymenium and subiculum, scattered to frequent, terminal or lateral, smooth, thin- to thick-walled, aseptate or with adventitious septa, (8–)15–30 × (4.5–)5–6.5(–8.5) μm. Basidioles clavate to subcylindrical, sometimes slightly tapering to apex, 7–22 × 4–5 μm. Basidia cylindrical, sometimes slightly constricted, 16–30 × 4–4.3 μm, thin-walled, smooth, with four sterigmata about 2.5 × 0.2 μm. Spores narrowly ellipsoid to oblong, 5–6(–6.3) × (2.5–)3–3.5 μm, holotype L = 5.5 μm, W = 3.2 μm, Q = 1.7, thin- or slightly thick-walled, colourless, smooth, with minute apiculus, inamyloid, indextrinoid, weakly cyanophilous.

Figure 8. 

Micromorphology of Xylodon pseudolanatus. CFMR: FP-150922 (holotype): A vertical section through basidioma B subicular hyphae C vertical section through aculeus D detail of subicular hyphae and hymenium E, F projecting aculeal hyphae in 3% KOH G projecting aculeal hyphae in water H projecting aculeal hyphae in Mz J capitate cystidia in hymenium K basidioles L basidiospores. CFMR: HHB-6925: M capitate cystidia in subiculum N basidia. Scale bars: 100 μm (A); 10 μm (C–K, M, N); 5 μm (B, L).

Distribution and ecology

South-eastern USA and Central America, on dead wood of angiosperms.

Etymology

From Greek pseudo- – false, refers to its similarity to X. lanatus.

Additional specimens examined

USA: Alabama, Escambia County, 3 miles east of Flomaton, on bark of Taxodium distichum (L.) Rich. (CFMR FP-103492), on bark of Quercus sp. (CFMR FP-103500), leg. A.S. Rhoades, 1 Nov 1952; Florida, Marion County, Okalawaha River, on dead inflorescence of Sabal palmetto (Walter) Lodd. ex Schult. & Schult. f., leg. H.H. Burdsall, Jr., 3 Aug 1972 (CFMR HHB-6925; dupl. in KAS and MSK); Louisiana, Baton Rouge, on Melia azedarach L., leg. C.J. Humphrey & C.W. Edgerton, 29 Aug 1909 (CFMR FP-5519).

Remarks

The diagnostic features of this species are the minutely odontioid hymenophore, bundles of sparsely to moderately encrusted hyphae, projecting from aculeal apices, embedded capitate cystidia, cylindrical basidia and narrowly ellipsoid basidiospores. Some hymenial elements in this species are intermediate in morphology between basidioles, capitate cystidia and hyphal ends. Xylodon pseudolanatus can be distinguished from similar species in the key below (see Discussion).

Xylodon hyphodontinus (Hjortstam & Ryvarden) Riebesehl, Yurchenko & G.Gruhn, comb. nov.

MycoBank No: MB827758
Fig. 6

Odontiopsis hyphodontina Hjortstam & Ryvarden, Mycotaxon 12(1): 180 (1980) (Basionym). Typus of O. hyphodontina: TANZANIA, Morogoro Prov., Morogoro distr., Uluguri Mts., Morning Side Res. sta. ca. 5 km S of Morogoro, substrate unknown, leg. L. Ryvarden, 24–26 Feb 1973 (O L. Ryvarden 10949 – holotype).

= Hydnum ambiguum Berk. & Broome, Journal of the Linnean Society, Botany 14(73): 60 (1873). Typus of H. ambiguum: SRI LANKA, Central Province, on dead wood (Berkeley No. 974 – holotype).

= Odontiopsis ambigua (Berk. & Broome) Hjortstam, Mycotaxon 28(1): 35 (1987).

= Pteridomyces sphaericosporus Boidin, Lanq. & Gilles, Mycotaxon 16(2): 490 (1983).

Remarks

This new combination is based on the phylogenetic analyses of the ITS and 28S sequences as well as morphological study of specimens, including the holotype of O. hyphodontina. Originally, the collections from Martinique and French Guyana were identified as O. ambigua, but the molecular data clearly show that these collections are embedded in Xylodon (Figs 1, 2). Although H. ambiguum is the oldest name for this taxon, it cannot be transferred to Xylodon because the name is preoccupied by X. ambiguus (Peck) Kuntze (= Veluticeps ambigua (Peck) Hjortstam & Telleria). Odontiopsis ambigua, P. sphaericosporus and O. hyphodontina were recognised as conspecific by Hjortstam (1987, 1991). Odontiopsis hyphodontina is the next oldest name and is chosen to represent this taxon. As O. hyphodontina is also the type of Odontiopsis Hjortstam & Ryvarden, Odontiopsis concomitantly becomes a synonym of Xylodon.

The newly generated ITS and 28S sequences of X. hyphodontinus hold comparable positions in a clade that includes three distinct lineages in both phylogenetic trees (Figs 1, 2). Specimens KAS-GEL9222 from Kenya and LIP GG-GUY13-044 from French Guyana each represent distinct lineages from the third lineage of LIP GG-MAR15-127 and LIP GG-MAR12-238 from Martinique. As species in Hyphodontia s.l. can be readily distinguished with ITS or 28S sequences, these three lineages should result in the recognition of three different species. However, we were not able to identify any definite morphological differences amongst the lineages in comparison with the holotype material from Tanzania. Cultures are not available for these specimens, thus intercompatibility tests are not possible. As a result, we decided to treat all three lineages as X. hyphodontinus at this time.

Xylodon vesiculosus Yurchenko, Nakasone & Riebesehl, nom. nov.

MycoBank No: MB827759
Figs 3e, 9

Replaced synonym

Odontia vesiculosa G. Cunn., Transactions and Proceedings of the Royal Society of New Zealand 86(1): 75 (1959) nom. inval.

Typus

NEW ZEALAND: Otago, Alton Valley, Tuatapere, leg. J.M. Dingley, Feb 1954 (PDD-18112 – holotype).

Cunningham (1959) described this new taxon as Odontia vesiculosa G. Cunn. Earlier, Odontia vesiculosa Burt was used for another species (Povah 1929). Consequently, Odontia vesiculosa G. Cunn. is an illegitimate name and a new name is required for this taxon (see Art. 6.11, 7.4 and 58.1 in Turland et al. 2018).

Below is a description based on the isotype of X. vesiculosus (CFMR).

Description

Basidiomata effused, odontioid, membranaceous, with a densely odontioid, ochraceous hymenial surface. Margin mostly abrupt, some parts thinning out. Hymenophoral aculei cylindrical to conical, acute apically, 130–350 μm long, 60–150 μm diam. at base, 4 per mm. Subiculum 100–150 μm thick, minutely cracking. Hyphal system monomitic; hyphae clamped at all primary septa. Subicular and tramal hyphae thick-walled (wall up to 1.5 μm), 2.5–4 μm wide, often with narrow lumen, smooth, colourless, looking faint yellowish in mass due to refractive walls. Subhymenium well developed; hyphae richly branched, thin- to slightly thick-walled, yellowish in mass. Aculei bearing skeletal-like, naked or poorly encrusted, immersed hyphal ends and variously encrusted, thick-walled, projecting hyphae in bunches, 3.5–5 μm wide. Capitate elements common, as lateral branches on tramal or subhymenial hyphae, (25–)30–55 × 6.5–10.5 μm, thin- to thick-walled, aseptate or with 1–2 adventitious septa. Basidioles clavate, subcylindrical, utriform. Basidia utriform to subcylindrical and clavate, 15–22 × 4–5 μm, thin-walled, smooth, with four sterigmata ca. 2 × 0.5 μm. Spores ellipsoid to narrowly ellipsoid or short cylindric, 5.3–6.3(–7) × 3–4 μm, holotype L = 5.9, W = 3.4, Q = 1.8 (n = 22), with adaxial side flat to convex, smooth, thin-walled, colourless, with minute apiculus, inamyloid, indextrinoid, acyanophilous.

Remarks

This species was considered conspecific with Xylodon lanatus from North America (Burdsall and Nakasone 1981, Wu 1990, Gorjón and Greslebin 2012), but we observed significant morphological differences. For example, in X. vesiculosus, the basidiomata have a denser, tough-membranaceous texture compared to the soft woolly basidiomata of X. lanatus. In addition, the aculei in X. vesiculosus are larger and the basidia are thin-walled in contrast to the smaller aculei and basally thick-walled basidia found in X. lanatus (compare Figs 9, 10). See Discussion for a key to X. lanatus, X. vesiculosus and allied taxa.

Figure 9. 

Micromorphology of Xylodon vesiculosus (PDD-18112, isotype): A vertical section through basidioma B subicular hyphae C excerpt of tramal hyphae to hymenium and skeletoid hyphae D bundle of projecting aculeal hyphae E smooth and variously encrusted aculeal hyphae F capitate cystidia G portion of hymenium and subhymenium H basidioles J basidia K basidiospores. Scale bars: 250 µm (A); 10 μm (B–J); 5 μm (K).

Figure 10. 

Micromorphology of Xylodon lanatus (CFMR: HHB-8925, holotype): A vertical section through basidiomata B subicular hyphae C vertical section through aculei and hymenium D projecting hyphae in 3% KOH E projecting hyphae in Mz F capitate cystidia G basidioles H basidia J basidiospores. Scale bars: 500 μm (A); 20 μm (C); 10 μm (B, D–H); 5 μm (J).

Xylodon niemelaei (Sheng H.Wu) Hjortstam & Ryvarden, Synopsis Fungorum 26: 28 (2009)

Hyphodontia niemelaei Sheng H. Wu, Acta Botanica Fennica 142:98 (1990).

Xylodon rhizomorphus (C.L.Zhao, B.K.Cui & Y.C.Dai) Riebesehl, Yurchenko & Langer, Mycological Progress 16(6): 649 (2017).

Hyphodontia rhizomorpha C.L.Zhao, B.K.Cui & Y.C.Dai, Cryptogamie, Mycologie 35(1):92 (2014).

Xylodon reticulatus (C.C.Chen & Sheng H.Wu) C.C.Chen & Sheng H.Wu, Mycoscience 59(5): 349 (2018).

Hyphodontia reticulata C.C.Chen & Sheng H.Wu, Mycological Progress 16(5): 558 (2017).

Remarks

Molecular and morphological analyses demonstrate that the three taxa listed above are very similar. The 11 samples of X. niemelaei, 3 of X. rhizomorphus and 3 of X. reticulatus formed a strongly supported clade (99 BS, 1 PP) in the ITS phylogram (Fig. 1). In addition, three samples representing two of the species are found in a strongly supported clade (100 BS, 1 PP) in the 28S tree (Fig. 2), differing in only one position in the associated alignment.

Xylodon niemelaei was described and illustrated in detail by Wu (1990) and Langer (1994). It is characterised by a poroid hymenophore, embedded and hymenial capitate cystidia, small, subulate or fusoid hymenial cystidia and encrusted hyphal ends mainly developed at the pore edges but sometimes also in other areas. At the morphological level, the bladder-like embedded cystidia and hyphal encrustations appear identical in X. niemelaei (Langer 1994), X. rhizomorphus (Zhao et al. 2014) and X. reticulatus (Chen et al. 2017). Spore size and spore quotient overlap in these three species. Xylodon rhizomorphus occurs in south-western China, whereas X. reticulatus occurs in Taiwan and Japan. Xylodon niemelaei is reported also from these three countries and furthermore from Réunion, Africa and South America (Langer 1994), but the last two reports require morphological and molecular confirmation.

Specimens examined

Xylodon niemelaei – REUNION: Forêt Mare-Longue, on dead stump of angiosperm wood, leg. J. Riebesehl, M. Schröder, M.M. Striegel, 12 Mar 2015 (FR-0249846, dupl. as L1087 in KAS); on lumber, leg. J. Riebesehl, M. Schröder, M.M. Striegel, 12 Mar 2015 (FR-0249174, dupl. as L1077 in KAS); on brown-rotten wood, leg. E. Langer, G. Langer, E. Hennen, 21 Mar 1998 (KAS-GEL 4998); Forêt Notre-Dame de la Paix, on dead wood of Monimia rotundifolia Thouars, leg. E. Langer, 11 Mar 2013 (FR-0219860, dupl. as L0002 in KAS); on dead angiosperm wood, leg. J. Riebesehl, M. Schröder, M.M. Striegel, 10 Mar 2015 (FR-0249811, dupl. as L1031 in KAS); on white-rotten wood, leg. E. Langer, G. Langer, E. Hennen, 19 Mar 1998 (KAS-GEL 4904); Le Petit Tampon, on dead wood, leg. J. Riebesehl, M. Schröder, M.M. Striegel, 9 Mar 2015 (FR-0249225, dupl. as L1007 in KAS); Piton Mont Vert, on dead wood, leg. J. Riebesehl, M. Schröder, M.M. Striegel, 18 Mar 2015 (FR-0249178, dupl. as L1172 in KAS); Plaine des Fougères, on dead wood, leg. E. Langer, 12 Sep 2013 (FR-0249744, dupl. as L0698 in KAS); Sentier de Takamaka, on white-rotten wood, leg. J. Riebesehl, M. Schröder, M.M. Striegel, 26 Mar 2015 (FR-0249289, dupl. as L1269 in KAS).

Xylodon spathulatus (Schrad.) Kuntze, Revisio generum plantarum (Leipzig) 3(2):541 (1898)

Hydnum spathulatum Schrad., Spicilegium Florae Germanicae: 178, t. 4:3 (1794).

= Hyphodontia bubalina Min Wang, Yuan Y.Chen & B.K.Cui, Phytotaxa 309(1):50 (2017).

Xylodon bubalinus (Min Wang, Yuan Y.Chen & B.K.Cui) C.C.Chen & Sheng H.Wu, Mycoscience 59:349 (2018).

= Hyphodontia chinensis C.C.Chen & Sheng H.Wu, Mycological Progress 16(5): 554 (2017).

Xylodon chinensis (C.C.Chen & Sheng H.Wu) C.C.Chen & Sheng H.Wu, Mycoscience 59: 349 (2018).

Remarks

Based on both molecular data and morphology, we place the taxa X. bubalinus and X. chinensis in synonymy under X. spathulatus. In our phylogenetic analysis of ITS sequence data, the recently described X. bubalinus (4 collections) and X. chinensis (2 collections) from China form a well-supported clade with X. spathulatus (4 collections) from Europe (97 BS, 1 PP) that is sister to X. apacheriensis (Fig. 1). Within this clade are several subclades, with very low bootstrap support (<55), thus subspecies or varieties cannot be identified. The 28S rRNA gene analysis also supports conspecificity between X. chinensis and X. spathulatus (99 BS, 0.65 PP) (Fig. 2). Xylodon spathulatus has three main diagnostic features: prominent (1–2 mm tall) aculei of varied shape, numerous apically acute cystidia with 1–4 slight constrictions and capitate cystidia with a resinous cap. It is described and illustrated by Eriksson and Ryvarden (1976) and Langer (1994). Minor morphological variation amongst the three taxa was observed. For example, X. chinensis has ventricose cystidia, similar to those in X. spathulatus, but they are sometimes septate at the constrictions. Distinctly ventricose cystidia were not observed in X. bubalinus, which instead had hyphoid or subulate cystidioles (Wang and Chen 2017, Fig. 2f). Encrusted hyphal ends at apices of the aculei in X. bubalinus and X. chinensis are typical of those in X. spathulatus. Resinous caps enclosing capitate elements are often absent as in the case of X. bubalinus, X. chinensis, X. spathulatus KAS-GEL2690 (from Germany) and X. spathulatus MSK-F 12931 (from Russia). Spore shape and size are similar amongst the three taxa and the spore quotient 1.3–1.4(–1.5) overlaps (Eriksson and Ryvarden 1976, Wang and Chen 2017, Chen et al. 2017). A few spores in X. chinensis were up to 6 × 5 μm and may be due to better climatic conditions. The description of X. spathulatus is modified to include variable aculei from conical and subulate to distinctly spathuliform and the variable presence of cystidia with resinous caps, mucronate apices and a submoniliform type that are aseptate with more or less blunt apices. Thus X. spathulatus is a highly variable but distinctive species that is widely distributed from northern Europe (Eriksson and Ryvarden 1976) to southern China (Chen et al. 2017) and has a preference for old-growth forests (Dvořák et al. 2017). Reports of X. spathulatus from North and South America (Ginns and Lefebvre 1993, Hjortstam and Ryvarden 2007b) should be confirmed by molecular sequence data.

Specimens examined

Xylodon spathulatus – CZECH REPUBLIC: Zofinsky National Park, on dead deciduous wood, leg. M.M. Striegel, 16 Sep 2015 (KAS-MMS 7224); GERMANY: Baden-Wurttemberg, Bad Waldsee, on dead wood of Picea abies (L.) H.Karst., leg. E. Langer, G. Langer, 15 Oct 1992 (KAS-GEL 2690); SWEDEN: Gästrikland, Island Torrö, on dead wood of Betula sp., leg. K.H. Larsson, 29 Sep 1988 (GB KHL 7085, dupl. in KAS); RUSSIA: Udmurtia, near Izhevsk town, on Sorbus aucuparia L., leg. V.I. Kapitonov, 7 Aug 2012 (MSK-F 12931).

Xylodon cystidiatus (A.David & Rajchenb.) Riebesehl & Langer, Mycological Progress 16(6):645 (2017)

Schizopora cystidiata A. David & Rajchenb., Mycotaxon 45:140 (1992).

Remarks

We undertook a thorough morphological analysis of the specimen FR-0249200 (Réunion, Plaine des Fougères, on fallen angiosperm twig, leg. E. Langer, 12 Sep 2013), because it provided the first sequences of X. cystidiatus. We are confident that FR-0249200 is X. cystidiatus, although we detected minor differences from the descriptions in David and Rajchenberg (1992) and Langer (1994). Some of the differences we noticed include: (1) the encrusted cystidia in FR-0249200 are mostly thin-walled with finer crystals; (2) the spores in our specimen were slightly broader 5–6 × 3.5–4.3 µm (L = 5.4 µm, W = 3.9 µm, Q = 1.4) than in published records 5–6 × 3–4 µm. Photographs of the basidioma (Fig. 11) and drawings of the microscopic features (Fig. 12) of FR-0249200 are provided for future identifications.

Figure 11. 

Basidioma of Xylodon cystidiatus (FR-0249200). Scale bar: 1 cm.

Figure 12. 

Micromorphology of Xylodon cystidiatus (FR-0249200): A subicular hyphae B crystals from dissepiment in 3% KOH C crystals from dissepiment in Mz D portion of hymenium and subhymenium E hyphal endings from dissepiment edges F encrusted cystidia in 3% KOH G encrusted cystidia in Mz H smooth basidioles and cystidioles J encrusted basidiole (in Mz) K basidia L basidiospores. Scale bars: 10 μm (A–K); 5 μm (L).

Discussion

We recognise 77 species of Xylodon based on studies by Riebesehl and Langer (2017), Chen et al. (2017, 2018), Kan et al. (2017), Wang and Chen (2017) and results herein (Table 1). Our phylogenetic analyses included 122 ITS and 28S sequences representing 37 Xylodon species. The other 40 accepted species in Xylodon are based on morphological studies.

In the following discussion, we highlight some of the significant results.

Odontiopsis is a synonym of Xylodon

The monotypic Odontiopsis Hjortstam & Ryvarden was described in 1980 based on O. hyphodontina from Tanzania. Hjortstam (1987) transferred Hydnum ambiguum to Odontiopsis and placed O. hyphodontina in synonymy. Later, Pteridomyces sphaericosporus was placed in synonymy with O. ambigua by Hjortstam (1991). Analyses of ITS and 28S sequences placed specimens originally identified as O. ambigua in the Xylodon lineage. Due to nomenclature rules to choose the earliest possible epithet to represent a taxon (see Art. 11.4 in Turland et al. 2018), the name for this taxon is Xylodon hyphodontinus and Odontiopsis is reduced to a synonym of Xylodon.

Palifer is a synonym of Xylodon

Species in Palifer have apically encrusted cystidia that are characteristic of the genus and distinctly different from the lagenocystidia of Hyphodontia s.s. (Hjortstam and Ryvarden 2009, Riebesehl and Langer 2017). Palifer is defined primarily by morphology because there is only a single ITS sequence available. Phylogenetic studies place P. verecundus amongst the Xylodon species (Larsson et al. 2006, Fig. 1). The recently described X. mollissimus has cystidia that are similar to those of Palifer species and ITS sequence analyses place it in a clade with Xylodon sp. 1 (Kan et al. 2017, Fig. 1). Although not closely related, X. mollissimus and P. verecundus are embedded within Xylodon and demonstrate that the distinctive cystidia developed in Palifer is not a phylogenetically significant character. Thus, we reduce Palifer to a synonym of Xylodon and propose the following transfers:

Xylodon erikssonii (M.Galán & J.E.Wright) Riebesehl & Langer, comb. nov.

MycoBank No: MB827760

Grandinia erikssonii M.Galán & J.E.Wright, in Galán, Lopez & Wright, Darwiniana 32(1–4):251 (1993) (Basionym).

Hyphodontia erikssonii (M.Galán & J.E.Wright) Hjortstam & Ryvarden, Synopsis Fungorum 20: 63 (2005).

Palifer erikssonii (M.Galán & J.E.Wright) Riebesehl, Yurchenko & Langer, in Riebesehl & Langer, Mycological Progress 16(6): 646 (2017).

Typus

ARGENTINA, Prov. Bonariae, Videla Dorna, on Salix babylonica L., May 1972, Deschamps et al. (BAFC 31920 – holotype).

Xylodon gamundiae (Gresl. & Rajchenb.) Riebesehl & Langer, comb. nov.

MycoBank No: MB827761

Hyphodontia gamundiae Gresl. & Rajchenb., Mycologia 92(6):1159 (2000) (Basionym).

Palifer gamundiae (Gresl. & Rajchenb.) Hjortstam & Ryvarden, Synopsis Fungorum 22: 9 (2007).

Typus

ARGENTINA, Tierra del Fuego, Dpto. Ushuaia, Estancia El Valdéz, on Nothofagus pumilio (Poepp. & Endl.) Krasser, 4–5 Mar 1996, A. Greslebin (BAFC 50036 – holotype).

Xylodon hjortstamii (Gresl. & Rajchenb.) Riebesehl & Langer, comb. nov.

MycoBank No: MB827762

Hyphodontia hjortstamii Gresl. & Rajchenb., Mycologia 92(6):1160 (2000) (Basionym).

Palifer hjortstamii (Gresl. & Rajchenb.) Hjortstam & Ryvarden, Synopsis Fungorum 22: 9 (2007).

Typus

ARGENTINA, Tierra del Fuego, Parque Nacional Tierra del Fuego, Río Pipo, on Nothofagus sp., 7 Nov 1998, A. Greslebin (BAFC 50037 – holotype).

Xylodon septocystidiatus (H.X.Xiong, Y.C.Dai & Sheng H.Wu) Riebesehl & Langer, comb. nov.

MycoBank No: MB827764

Hyphodontia septocystidiata H.X.Xiong, Y.C. Dai & Sheng H.Wu, Mycologia 102(4):918 (2010) (Basionym).

Palifer septocystidiatus (H.X.Xiong, Y.C.Dai & Sheng H.Wu) Riebesehl, Yurchenko & Langer, in Riebesehl & Langer, Mycological Progress 16(6): 649 (2017).

Typus

TAIWAN, Taipei, Kungliao, on rotten angiosperm branch, 25 Nov 1990, Y.F. Lin (TNM Lin 90202 – holotype).

Xylodon verecundus (G.Cunn.) Yurchenko & Riebesehl, comb. nov.

MycoBank No: MB827765

Peniophora verecunda G.Cunn., Transactions and Proceedings of the Royal Society of New Zealand 83(2):262 (1955) (Basionym).

Palifer verecundus (G.Cunn.) Stalpers & B.K.Buchanan, New Zealand Journal of Botany 29(3): 339 (1991).

Hyphodontia verecunda (G.Cunn.) Hjortstam & Ryvarden, Mycotaxon 64: 237 (1997).

Typus

NEW ZEALAND, Auckland, Hauhangaroa Range, Taupo, on decayed decorticated wood of Dacrydium cupessinum Sol., Mar 1953, J.M. Dingley (PDD 12513 – holotype).

Notes

The three species Palifer rickii (Hjortstam & Ryvarden) Riebesehl, Yurchenko & Langer, P. seychellensis Dämmrich & Rödel and P. wrightii (Hjortstam & Ryvarden) Hjortstam & Ryvarden are today already accepted in other genera as Xylodon rickii (Hjortstam & Ryvarden) K.H. Larss. (Viner et al. 2018), Sceptrulum inflatum (Burt) K.H. Larss. (Larsson 2014) and Hyphodontia wrightii Hjortstam & Ryvarden (Gorjón 2012).

Xylodon lanatus and allied species

Xylodon lanatus was originally described by Burdsall and Nakasone (1981) based on collections from North America and New Zealand. A comparative morphological study of specimens, annotated as X. lanatus from Taiwan and North America, revealed that X. lanatus is a complex of morphologically similar species. The New Zealand specimen, X. vesiculosus, was discussed above and is considered to be a distinct species. The specimen X. lanatus (TUB-FO 40734) from Taiwan, depicted in Langer (1994), is X. exilis. The specimen of X. lanatus cited by Hjortstam and Ryvarden (1984) from Nepal is also X. exilis. In the protologue of X. lanatus (Burdsall and Nakasone 1981), the authors illustrated the paratype (HHB-6925 from Florida, U.S.A.) which is correctly identified as X. pseudolanatus. Hjortstam and Bononi (1987) reported X. lanatus from Brazil while noting the controversial taxonomic position of this species.

We accept X. lanatus, based on the type (CFMR HHB-8925; Figs 3f, 10) and paratype (CFMR HHB-4305), as a distinct species but with a restricted concept. We retain the same diagnostic features, noted in the protologue (basidiomata with well-developed woolly subiculum, terminal vesicular structures on subicular hyphae, poorly differentiated subhymenium, encrusted thick-walled hyphae in tooth apices and capitate cystidia) and add that walls of basidia and subhymenial hyphae directly under hymenial elements are slightly but distinctly thickened. The illustration of Xylodon lanatus from Taiwan, provided by Wu (1990), also shows basidia with walls thickened below, but hyphal pegs appear different from X. lanatus s.s. We have also determined that X. echinatus (Yurchenko et al. 2013) is the most morphologically similar species to X. lanatus s.s. A key to the taxa in the X. lanatus group is presented here.

1 Basidioma between aculei 0.3–0.5 mm thick, woolly; subhymenial hyphae somewhat thick-walled directly under hymenium 2
Basidioma between aculei 0.05–0.15 mm thick, membranaceous or subceraceous; subhymenial hyphae thin-walled 3
2 Capitate cystidia present; basidia with slightly thickened walls in lower ½–2/3; spores 3–3.5 μm broad, Q = 1.8–2 X. lanatus
Capitate cystidia absent; basidia thin-walled; spores 3.5–4(–5) μm broad, Q = 1.6–1.9 X. echinatus
3 Subicular hyphae strongly thick-walled (up to 1.5 μm thick), often with narrow lumen; hymenophoral aculei 0.13–0.35 mm long, 4 per mm X. vesiculosus
Subicular hyphae moderately thick-walled (up to 1–1.2 μm thick), with wide lumen; hymenophoral aculei 0.03–0.12 mm long, 8–14 per mm 4
4 Projecting hyphae in aculei strongly flexuous, thick-walled (up to 1–1.5 μm thick) in middle and lower part, provided with closely arranged simple and clamped septa, constricted at septa X. exilis
Projecting hyphae in aculei slightly flexuous, slightly thick-walled, with remote septa, not constricted at septa X. pseudolanatus

Phylogenetic analyses of ITS sequences of 17 samples, including 8 new sequences of X. niemelaei and 28S sequences of three samples, demonstrate that the three taxa are very similar (Figs 1, 2). ITS sequences from holotypes of X. reticulatus and X. rhizomorphus were included in the analyses (Fig. 1). The ITS sequences were 98.2–99% similar amongst the taxa, differing at 6–11 sites. Minor morphological differences were noted amongst the taxa. We keep the taxa X. niemelaei, X. reticulatus and X. rhizomorphus as separate species following the results of phylogenetic studies of Chen et al. (2017) and Fernández-López et al. (2018a). The last work was published shortly before the completion of our study and therefore could not be considered further.

However, in our reconstruction, the phylogenetic distances between these taxa are very short, and comparable to those between the OTUs of X. spathulatus. Taking into account that these three taxa remain as monophyletic branches, we suppose that they can be subspecies or varieties of one species.

Figure 13. 

Hymenophores of X. raduloides. A KAS-JR 02, Germany B KAS-JR 03, Germany C KAS-JR 09, Germany D KAS-JR 26, Germany E KAS-JR 10, Germany F LR18813, Australia. Scale bars: 1 cm.

Xylodon bubalinus, X. chinensis and X. spathulatus are conspecific

Phylogenetic analyses of ITS sequences of 10 samples, including sequences from holotypes of Xylodon bubalinus and X. chinensis and 28S sequences of X. spathulatus and holotype of X. chinensis show that the three taxa are conspecific (Figs 1, 2). Amongst the taxa, ITS sequences were 98.7–99.8% similar, differing at up to 8 sites. The hymenophore is quite variable in this group and the presence of the different types of cystidia is also variable. The correct name for this group is X. spathulatus with X. bubalinus and X. chinensis reduced to synonyms.

The classification of Xylodon australis in Xylodon is confirmed

Xylodon australis is sequenced for the first time and shown in the 28S phylogenetic tree (Fig. 2) and its placement in Xylodon is confirmed. The sequenced specimen is from Argentina and was studied by Greslebin et al. (2000). They reported differences in spore morphology in specimens from Argentina, Australia and New Zealand. A molecular study may be able to resolve this species complex.

The paratype material of Xylodon dimiticus may be an independent species

Chen et al. (2017) showed that the holotype material of Xylodon dimiticus (Jia J.Chen & L.W.Zhou) Riebesehl & Langer Dai 11686 is conspecific with X. nongravis. In addition, they also proposed that the paratype material Dai 15321 may be an independent species as shown in the phylograms. We support this view and included Dai 15321 in our phylograms as Xylodon sp. 1. The NCBI BLAST search of the ITS sequence of Dai 15321 shows an identity of 93% with the X. dimiticus holotype material Dai 11686 as well as with sequences of X. nongravis. Although this low similarity value indicates that Dai 15321 is a different species, a further study is needed to identify morphological differences.

Additions to the distribution and morphology of Xylodon serpentiformis

A BLAST search of the newly generated Xylodon serpentiformis ITS sequences revealed that they are 99% identical to a sequence from South Korea identified as Hyphodontia sp. (KUC20121019-31, Jang et al. 2016). Xylodon serpentiformis is known from Taiwan and the Canary Islands (Langer 1994). Based on the small distance between Taiwan and South Korea and the similarities of the sequences, the distribution of X. serpentiformis is expanded to include South Korea. Langer (1994) cited a specimen of X. serpentiformis from the Canary Islands, but this material needs molecular confirmation. A distinctive feature, described for this species, was the presence of flexuous, thick-walled tubular tramacystidia in the aculei (Langer 1994). After our morphological analysis of the holotype of Hyphodontia serpentiformis Langer (TUB-FO 40677) and three more specimens (TUB-FO 40675, TUB-FO 40985, TUB-FO 42688), we emend the diagnosis of X. serpentiformis as follows: aculei consisting mostly of flexuous, agglutinated projecting hyphae, hyphae slightly thickened or moderately thick-walled at base, then thinning toward apex and partly collapsing at maturity; spores broadly ellipsoid, ellipsoid, subovoid, sometimes narrowly ellipsoid.

Sequences of Xylodon raduloides form two subclades in phylogenetic trees

The two subclades of Xylodon raduloides in the ITS phylogeny (Fig. 1) appear also in the 28S phylogram (Fig. 2), although with the inclusion of the sister species X. subtropicus. Both subclades include specimens from Germany and Australia. Micromorphological distinctions between the clades were not observed, but we noted that, in one of the clades (KAS-JR 02, 03, 09, 26), the hymenophore is pale cream to cream whereas, in the second clade (KAS-JR10, LR 18813), it is yellow-brownish (Fig. 13). Nevertheless, the morphological as well as sequence-based differences are not sufficient to recognise two separate species.

Sequences of Xylodon flaviporus form two subclades in phylogenetic trees

In the ITS phylogram, two subclades are also present in the Xylodon flaviporus lineage (Fig. 1). Subclade 1 (FR-0249797, KAS-GEL 5047) comprises specimens from Réunion whereas subclade 2 (FCUG 1053, KAS-GEL 3462) comprises specimens from Romania and Taiwan. All other ITS sequences of X. flaviporus from the NCBI GenBank are from the northern hemisphere (Romania, South Korea, Taiwan, Turkey and USA) and clustered together in subclade 2 (data in Fig. 1 are reduced to specimens from Romania and Taiwan). We did not find micromorphological differences between specimens of the two subclades and the variation in the ITS sequences is too small to merit recognition of two different species.

Xylodon ramicida and X. quercinus

Xylodon ramicida and X. quercinus are morphologically similar (Ariyawansa et al. 2015), exhibiting slight differences in spore width and shape and different substrate preferences. Their ITS sequences are 98.8–99% similar, differing at just 6–7 positions (X. quercinus: Miettinen 15050 and X. ramicida: Spirin 7664). Taking into account the similarity values of other Xylodon species (X. spathulatus 98.7–99%, X niemelaei 98.2–99%) and small morphological differences between X. ramicida and X. quercinus, we believe that X. ramicida is a well-defined subspecies within X. quercinus. More sequences from both taxa are required, however, before the taxonomic status of X. ramicida can be clarified.

The taxonomic status of Xylodon detriticus

In this study, we accept Hyphodontia detritica (Bourdot) J. Erikss. in Xylodon as X. detriticus. This combination was introduced by Ţura et al. (2011), recognised as invalid in MycoBank (Art. 36.1a and b, Melbourne Code) and supported in the work by Rosenthal et al. (2017). The first sequenced specimen of this species was GB Nilsson 990902 (Larsson 2007). We have studied this specimen and it is identical to the concept of Hypochnicium detriticum (Bourdot) J. Erikss. & Ryvarden (Eriksson and Ryvarden 1976). The alignment between GB Nilsson 990902 and X. detriticus UC2023108 (Rosenthal et al. 2017) in ITS2 (ITS1 is unavailable for the previous specimen) showed nearly 100% similarity. We discovered that the ITS2 sequences between Lagarobasidium detriticum MA-Fungi 5758 (Dueñas et al. 2009) and GB Nilsson 990902 were 62% identical. Consequently, the taxonomic identity of Lagarobasidium detriticum MA-Fungi 5758 needs to be investigated. Viner et al. (2018) came to the same conclusion, but we could not integrate their further results, because this study was already finished when the work of Viner et al. was published.

Conclusion

The usefulness of ITS sequences alone in defining and identifying species in Xylodon is approaching its limits. Further studies in Xylodon will require sequences from additional genetic markers with more variation. Fernández-López et al. (2018b) published the first phylogenetic tree for Xylodon with rpb2 sequences, but it contains only sequences of six different species. Nevertheless, the topology is very similar to our ITS and 28S trees.

Morphological features for defining species in Xylodon is also limited. Species, such as X. spathulatus with its variability in aculei morphology and in cystidia occurrence and shape, present challenges for identification. In other cases such as X. hyphodontinus, ITS sequence differences are significant whereas morphological differences are elusive.

Acknowledgements

The financial support for collection trips to Réunion by the Hessian Ministry of Higher Education, Research and Arts (IPF excellence cluster for integrative fungal research; LOEWE Landesoffensive zur Entwicklung wissenschaftlich-ökonomischer Exzellenz) is gratefully acknowledged. We are very thankful for the technical support of Ulrike Frieling, Sylvia Heinemann and Christian Witzany, as well as Jonathan Denecke, Felix Pansegrau, Lukas Langer, Anne Ende, Alexander Concha Vega, Nina Büchner, Shiyan Liao and Jan Moritz Böhme for their help with generating sequences. We are grateful to Alexander Ordynets for first classifications of specimens from Réunion, Manuel Striegel and Gérald Gruhn for providing specimens and first analyses, Karl-Henrik Larsson and the University of Oslo for providing the type of Odontiopsis hyphodontina and Ellen Larsson and the University of Gothenburg for providing a specimen of Hyphodontia detritica. The editor and the reviewers are acknowledged for critical considerations of the manuscript.

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