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Reassessment of the generic limits for Hydnellum and Sarcodon (Thelephorales, Basidiomycota)
expand article infoKarl-Henrik Larsson§, Sten Svantesson|§, Diana Miscevic#, Urmas Kõljalg¤, Ellen Larsson§
‡ University of Oslo, Oslo, Norway
§ Gothenburg Global Biodiversity Centre, Göteborg, Sweden
| Royal Botanic Gardens Victoria, Victoria, Australia
¶ University of Gothenburg, Göteborg, Sweden
# Unaffiliated, Vallda, Sweden
¤ Institute of Ecology and Earth Sciences, Tartu, Estonia
Open Access

Abstract

DNA sequences from the nuclear LSU and ITS regions were used for phylogenetic analyses of Thelephorales with a focus on the stipitate hydnoid genera Hydnellum and Sarcodon. Analyses showed that Hydnellum and Sarcodon are distinct genera but that the current division, based on basidioma texture, makes Sarcodon paraphyletic with respect to Hydnellum. In order to make genera monophyletic several species are moved from Sarcodon to Hydnellum and the following new combinations are made: Hydnellum amygdaliolens, H. fennicum, H. fuligineoviolaceum, H. fuscoindicum, H. glaucopus, H. joeides, H. lepidum, H. lundellii, H. martioflavum, H. scabrosum, H. underwoodii, and H. versipelle. Basidiospore size seems to separate the genera in most cases. Hydnellum species have basidiospore lengths in the range 4.45−6.95 µm while the corresponding range for Sarcodon is 7.4−9 µm. S. quercinofibulatus deviates from this pattern with an average spore length around 6 µm. Neotropical Sarcodon species represent a separate evolutionary lineage.

Keywords

Phylogeny, stipitate hydnoid, taxonomy, Thelephorales, tooth fungi

Introduction

The order Thelephorales is a distinctive lineage of Agaricomycetes, well-known for its almost ubiquitous ectomycorrhizal life style (Tedersoo et al. 2010). Several species have stipitate hydnoid basidiomata (Fig. 1). They have traditionally been divided into four genera, Phellodon and Bankera with hyaline basidiospores, and Hydnellum and Sarcodon with yellow to brown tinted basidiospores (Maas Geesteranus 1975). In both cases the genera within each pair differ in basidioma structure, with Phellodon and Hydnellum being hard and dry, and Bankera and Sarcodon forming softer, fleshier basidiomata. This difference in texture is, however, difficult to assess and a series of recent molecular phylogenetic analyses, as outlined below, have indicated that the traditional, morphology-based generic limits are equivocal.

Figure 1. 

Fruiting bodies of Hydnellum and Sarcodon A Hydnellum suaveolens B H. aurantiacum C H. ferrugineum D Sarcodon imbricatus.

In a recent comprehensive study of stipitate hydnoid species from south-eastern North America, Baird et al. (2013) found that Bankera could not be separated from Phellodon and the genera were hence combined into a more comprehensive Phellodon. The same study suggested that the generic limits of Sarcodon and Hydnellum need reassessment.

Nitare and Högberg (2012) examined the Nordic species of Sarcodon and included a preliminary molecular phylogeny for the species accepted in Sarcodon. Hydnellum species were also included in non-published test runs and found to be nested among Sarcodon species. They concluded that revisions of limits of both genera were probably necessary. Miscevic (2013) expanded on the results in Nitare and Högberg (2012) by including more sequences for each species and by including a selection of Hydnellum species in published phylogenies. The results were in congruence with Baird et al. (2013) with regard to overall tree topology and again the conclusion was that the limits of Sarcodon and Hydnellum need further study. A recent phylogenetic overview of Thelephorales (Vizzini et al. 2016) and a study of Hydnellum from the Mediterranean region (Loizides et al. 2016) came to similar conclusions, although Vizzini et al. (2016) did not include sequences from several Neotropical Sarcodon species described by Grupe et al. (2015, 2016).

In this paper we analyse ITS and nuclear LSU sequences from a wide selection of Thelephorales species with a focus on Hydnellum and Sarcodon in order to resolve the relationship between these two genera. We also make some nomenclatural changes that follow from the revision of genus circumscriptions. We demonstrate that Neotropical Sarcodon species do not cluster with temperate and boreal species and may be warranted as one or more new genera with more data.

Methods

For the phylogenetic analyses we compiled two datasets. The first dataset consists of nuclear LSU sequences from most genera in Thelephorales and from a majority of the Hydnellum and Sarcodon species occurring in Europe. For our two target genera we chose only sequences generated for this study from recently collected basidiomata. We deliberately excluded sequences from specimens identified as H. concrescens or H. scrobiculatum since these names seem to cover more than just two species and it is currently unclear how the names should be applied (Ainsworth et al. 2010). Since this study is positioned as a revision of the genus limits we were more interested in sequence quality control than a complete coverage of all species reported from Europe.

For our second dataset we chose a different strategy. Here we included ITS sequences from all Hydnellum and Sarcodon species represented among our own sequences and in GenBank as of December 1, 2018. The reason is that many species, and especially the recently described species from tropical regions, are only available as ITS sequences. However, we made no attempt to verify the identifications given in GenBank and do not endorse them as correct.

DNA was extracted from recent dried collections of basidiomata from North Europe. Voucher numbers, herbarium location, and GenBank numbers are given in Table 1. DNA extraction and PCR protocols follow Larsson et al (2018). Sequencing was either done in-house at University of Oslo, or as a commercial service by Macrogen Inc., South Korea. Assembly of chromatograms was done with Sequencher 5.2.4 (Gene Codes Co., Ann Arbor). Aligning was performed either manually using the editor in PAUP* 4.0a (Swofford 2002) or the software ALIVIEW 1.18 (Larsson 2014), or automatically utilising the L-INS-i strategy as implemented in MAFFT v. 7.017 (Katoh and Standley 2013), followed by manual adjustment.

Specimens sequenced or downloaded from GenBank. Herbarium acronyms follow Thiers. Sequences generated for this study are marked in bold.

Species Voucher Herb. GenBank number
ITS LSU
Amaurodon aquicoeruleus Agerer Agerer & Bougher M AM490944 AM490944
Amaurodon viridis (Alb. & Schwein.:Fr.) J.Schröt KH Larsson 14947b O MK602707 MK602707
Bankera fuligineoalba (J.C.Schmidt:Fr.) Pouzar E Larsson 400-13 GB MK602708 MK602708
Bankera violascens (Alb. & Schwein.:Fr.) Pouzar MV 130902 GB MK602709 MK602709
Boletopsis leucomelaena (Pers.:Fr.) Fayod M Krikorev 140912 GB MK602710 MK602710
Hydnellum aurantiacum (Batsch:Fr.) P.Karst. RG Carlsson 08-105 GB MK602711 MK602711
Hydnellum aurantiacum E Bendiksen 177-07 O MK602712 MK602712
Hydnellum aurantiacum O-F-295029 O MK602713 MK602713
Hydnellum auratile (Britzelm.) Maas Geest. O-F-294095 O MK602714 MK602714
Hydnellum auratile O-F-242763 O MK602715 MK602715
Hydnellum auratile J Nitare 110926 GB MK602716 MK602716
Hydnellum caeruleum (Hornem.:Fr.) P.Karst. O-F-291490 O MK602717 MK602717
Hydnellum caeruleum E Bendiksen 575-11 O MK602718 MK602718
Hydnellum caeruleum E Bendiksen 584-11 O MK602719 MK602719
Hydnellum complicatum Banker REB 71 KC571711
Hydnellum concrescens (Pers.) Banker K(M)134463 K EU784267
Hydnellum cristatum (G.F.Atk.) Stalpers REB 169 TENN JN135174
Hydnellum cumulatum K.A.Harrison SE Westmoreland 69 AY569026
Hydnellum cyanopodium K.A.Harrison SE Westmoreland 85 AY569027
Hydnellum diabolus Banker KAH 13873 MICH AF351863
Hydnellum dianthifolium Loizides, Arnolds & P.-A.Moreau ML61211HY KX619419
Hydnellum earlianum Banker REB 375 TENN JN135179
Hydnellum ferrugineum (Fr.:Fr.) P.Karst. O-F-297319 O MK602720 MK602720
Hydnellum ferrugineum E Larsson 356-16 GB MK602721 MK602721
Hydnellum ferrugineum E Larsson 197-14 GB MK602722 MK602722
Hydnellum ferrugipes Coker REB 176 KC571727
Hydnellum geogenium (Fr.) Banker O-F-66379 O MK602723 MK602723
Hydnellum geogenium O-F-296213 O MK602724 MK602724
Hydnellum geogenium E Bendiksen 526-11 O MK602725 MK602725
Hydnellum gracilipes (P.Karst.) P.Karst. E Larsson 219-11 GB MK602726 MK602726
Hydnellum gracilipes GB-0113779 GB MK602727 MK602727
Hydnellum mirabile (Fr.) P.Karst. RG Carlsson 11-119 GB MK602728 MK602728
Hydnellum mirabile E Larsson 170-14 GB MK602729 MK602729
Hydnellum mirabile S Lund 140912 GB MK602730 MK602730
Hydnellum peckii Banker S Svantesson 328 GB MK602731 MK602731
Hydnellum peckii E Larsson 174-14 GB MK602732 MK602732
Hydnellum peckii E Bendiksen 567-11 O MK602733 MK602733
Hydnellum pineticola K.A.Harrison RB 94 KC571734
Hydnellum piperatum Maas Geest. REB 322 TENN JN135173
Hydnellum regium K.A.Harrison SE Westmoreland 93 AY569031
Hydnellum scleropodium K.A.Harrison REB 3 TENN JN135186
Hydnellum scrobiculatum (Fr.) P.Karst. REB 78 TENN JN135181
Hydnellum spongiosipes (Peck) Pouzar REB 52 TENN JN135184
Hydnellum suaveolens (Scop.:Fr.) P.Karst. E Larsson 139-09 GB MK602734 MK602734
Hydnellum suaveolens E Larsson 8-14 GB MK602735 MK602735
Hydnellum suaveolens S Svantesson 877 GB MK602736 MK602736
Hydnellum subsuccosum K.A.Harrison REB 10 TENN JN135178
Lenzitopsis daii L.W.Zhou & Kõljalg Yuan 2959 IFP JN169799 JN169793
Lenzitopsis oxycedri Malençon & Bertault KH Larsson 15304 GB MK602774 MK602774
Odontia fibrosa (Berk. & M.A.Curtis) Kõljalg TU115028 TU MK602775 MK602775
Phellodon cf niger E Larsson 35-14 GB MK602782 MK602782
Phellodon tomentosus (L.:Fr.) Banker E Bendiksen 118-10 O MK602781 MK602781
Pseudotomentella flavovirens (Höhn. & Litsch.) Svrček KH Larsson 16190 O MK602780 MK602780
Sarcodon amygdaliolens Rubio Casas, Rubio Roldán & Català SC 2011 JN376763
Sarcodon aspratus (Berk.) S.Ito DQ448877
Sarcodon atroviridis (Morgan) Banker REB 104 TENN JN135190
Sarcodon atroviridis REB 61 KC571768
Sarcodon bairdii A.C.Grupe & Vasco-Pal. Vasco 990 HUA KR698938
Sarcodon colombiensis A.C.Grupe & Vasco-Pal. Vasco 2084 HUA KP972654
Sarcodon fennicus (P.Karst.) P.Karst. S Westerberg 110909 GB MK602739 MK602739
Sarcodon fennicus O-F-242833 O MK602738 MK602738
Sarcodon fennicus O-F-204087 O MK602737 MK602737
Sarcodon fuligineoviolaceus (Kalchbr.) Pat. LA 120818 GB MK602740 MK602740
Sarcodon fuligineoviolaceus B Nylén 130918 GB MK602741 MK602741
Sarcodon fuligineoviolaceus A Molia 160-2011 O MK602742 MK602742
Sarcodon fuscoindicus (K.A.Harrison) Maas Geest. OSC 113622 OSC EU669228
Sarcodon glaucopus Maas Geest. & Nannf. RG Carlsson 13-060 GB MK602743 MK602743
Sarcodon glaucopus J Nitare 060916 GB MK602744 MK602744
Sarcodon glaucopus Å Edvinson 110926 GB MK602745 MK602745
Sarcodon imbricatus (L.:Fr.) P.Karst. S Svantesson 355 GB MK602748 MK602748
Sarcodon imbricatus J Rova 140829-2 GB MK602746 MK602746
Sarcodon imbricatus E Larsson 384-10 GB MK602747 MK602747
Sarcodon joeides (Pass.) Bataille RG Carlsson 11-090 GB MK602749 MK602749
Sarcodon joeides K Hjortstam 17589 GB MK602750 MK602750
Sarcodon joeides J Nitare 110829 GB MK602751 MK602751
Sarcodon joeides REB 270 KC571772
Sarcodon lepidus Maas Geest. E Grundel 110916 GB MK602753 MK602753
Sarcodon lepidus RG Carlsson 10-065 GB MK602752 MK602752
Sarcodon lepidus J Nitare 110829 GB MK602754 MK602754
Sarcodon leucopus (Pers.) Maas Geest. & Nannf. O-F-296944 O MK602756 MK602756
Sarcodon leucopus O-F-296099 O MK602755 MK602755
Sarcodon leucopus P Hedberg 080811 GB MK602757 MK602757
Sarcodon lundellii Maas Geest. & Nannf. L&A Stridvall 06-049 GB MK602758 MK602758
Sarcodon lundellii O-F-242639 O MK602759 MK602759
Sarcodon lundellii O-F-295814 O MK602760 MK602760
Sarcodon martioflavus (Snell, K.A.Harrison & H.A.C.Jacks.) Maas Geest. A Delin 110804 GB MK602763 MK602763
Sarcodon martioflavus O-F-242435 O MK602762 MK602762
Sarcodon martioflavus O-F-242872 O MK602761 MK602761
Sarcodon pakaraimensis A.C.Grupe & T.W.Henkel T Henkel 9554 BRG KM668103
Sarcodon pallidogriseus A.C.Grupe & Vasco-Pal. Vasco 989 HUA KR698939
Sarcodon portoricensis A.C.Grupe & T.J.Baroni TG Baroni 8776 NY KM668100
Sarcodon quercophilus A.C.Grupe & Lodge CFMR-BZ-3833 NY KM668101
Sarcodon quercinofibulatus Pérez-De-Greg., Macau & J.Carbó JC 20090718-2 JX271818 MK602773
Sarcodon rufobrunneus A.C.Grupe & Vasco-Pal. Vasco 1989 HUA KR698937
Sarcodon scabripes (Peck.) Banker REB 351 TENN JN135191
Sarcodon scabrosus (Fr.) P.Karst. O-F-295824 O MK602764 MK602764
Sarcodon scabrosus O-F-292320 O MK602766 MK602766
Sarcodon scabrosus O-F-360777 O MK602765 MK602765
Sarcodon squamosus (Schaeff.) Quél. O-F-177452 O MK602768 MK602768
Sarcodon squamosus E Larsson 248-12 GB MK602767 MK602767
Sarcodon squamosus O-F-295554 O MK602769 MK602769
Sarcodon umbilicatus A.C.Grupe, T.J.Baroni & Lodge TJ Baroni 10201 NY KM668102
Sarcodon underwoodii Banker REB 50 KC571781
Sarcodon versipellis (Fr.) Nikol. RG Carlsson 13-057 GB MK602771 MK602771
Sarcodon versipellis RG Carlsson 11-085 GB MK602772 MK602772
Sarcodon versipellis E Bendiksen 164-07 O MK602770 MK602770
Sistotrema brinkmannii (Bres.) J.Erikss. KH Larsson 14078 GB KF218967 KF218967
Steccherinum ochraceum (J.F.Gmel.:Fr.) Gray KH Larsson 11902 GB JQ031130 JQ031130
Thelephora caryophyllea (Schaeff.:Fr.) Pers. E Larsson 89-09S GB MK602776 MK602776
Thelephora terrestris Ehrh.:Fr. E Larsson 295-13 GB MK602777 MK602777
Tomentella stuposa (Link) Stalpers Th-0764 O MK602778 MK602778
Tomentellopsis pulchella Kõljalg & Bernicchia KH Larsson 16366 O MK602779 MK602779

In the phylogenetic analyses we assumed the following minimal partitions for the nrDNA region: ITS1, 5.8S, ITS2 and LSU (approximately 1200 bases of the 5’ end). Two datasets were analysed separately: an LSU dataset only including the LSU region, and an ITS dataset including ITS1, 5.8S and ITS2. We used the automated best-fit tests implemented in PAUP* 4.0a (Swofford 2002) to select optimal substitution models for each complete, non-partitioned dataset (PHYML) and optimal substitution model partitions for each minimal partition (BEAST). Models and partitions were chosen based on BIC score for the BEAST analysis and AICc score for the PHYML analysis. All tests were conducted using three substitution schemes and evaluated substitution models with equal and gamma-distributed among-site rate variation. The tests for the PHYML analysis also evaluated substitution models with invariant sites. The following partitions and models had the highest ranking, according to BIC: ITS1+ITS2 (GTR+G), 5.8S (K80+G), LSU (GTR+G). According to AICc the GTR+I+G model provided the best fit for both the ITS and the LSU datasets.

To generate Bayesian phylogenetic trees (BI) from the alignments we used BEAST 2.4.7 (Bouckaert et al. 2014). We prepared the xml-files for the BEAST 2 runs in BEAUTI 2.4.7 (Bouckaert et al. 2014). We set the substitution model to GTR+G for the LSU run. In the ITS run we set it to HKY+G for 5.8S, since it is the most similar model to K80+G available in the program. Test runs revealed convergence problems due to insufficient data for some substitution rates in the GTR+G model initially used for the ITS1+ITS2 partition, and it was hence changed to HKY+G. In the ITS run the substitution rate of both partitions were estimated independently. We set the trees of the minimal nrDNA partitions as linked in this analysis and the clock models as unlinked. A lognormal, relaxed clock model was assumed for each partition, as test runs had shown that all partitions had a coefficient of variation well above 0.1 (i.e. implying a relatively high rate variation among branches). The clock rate of each partition was estimated in the runs, using a lognormal prior with a mean set to one in real space. We set the growth rate prior to lognormal, with a mean of 5 and a standard deviation of 2. We ran the Markov Chain Monte Carlo (MCMC) chains of both datasets for 20 million generations with tree and parameter files sampled every 1,000 generations. The analyses all converged well in advance of the 10 % burn-in threshold, had ESS values well above 200 for all parameters, and chain mixing was found to be satisfactory as assessed in TRACER 1.6.0 (Rambaut et al. 2014). After discarding the burn-in trees, maximum clade credibility trees were identified by TREEANNOTATOR 2.4.7 (Bouckaert et al. 2014).

To generate Maximum Likelihood (ML) gene trees we used PHYML 3.1 (Guindon et al. 2010). We set the substitution model to GTR+I+G for both the ITS and LSU datasets. Tree topology search was conducted using NNI+SPR, with ten random starting trees. Non-parametric bootstrap analyses with 1000 replicates were performed on the resulting trees.

Results

Seventy-five Thelephorales specimens from the genera Amaurodon, Bankera, Boletopsis, Hydnellum, Lenzitopsis, Phellodon, Pseudotomentella, Sarcodon, Thelephora, Tomentella, and Tomentellopsis, were sequenced for this study. In addition, 39 sequences were downloaded from public databases (GenBank, UNITE) including outgroup sequences of Steccherinum ochraceum (Polyporales) and Sistotrema brinkmannii (Cantharellales) included in the LSU dataset. The ITS analyses were rooted by the default method (BEAST) or left unrooted (PHYML).

The aligned LSU dataset consisted of 1443 nucleotide positions. After exclusion of ambiguous regions 1377 positions remained for the analyses. BI returned a tree where the focus genera Hydnellum and Sarcodon are distributed over two strongly supported clades. The larger of these clades includes the type of Hydnellum, H. suaveolens, and an additional 17 species, all except one forming strongly supported terminal clades. Nine of these taxa are currently placed in Sarcodon. With a few exceptions the relationships within Hydnellum are not resolved. H. aurantiacum and H. auratile are recovered as a strongly supported group; Sarcodon scabrosus and S. fennicus are grouped with 0.97 posterior probability support; S. fuligineoviolaceus, S. glaucopus, and S. joeides form a subclade with 0.97 posterior probability support; and finally H. suaveolens and S. versipellis form a strongly supported clade. The type of Sarcodon, S. imbricatus, and three other species form the second main clade. The three sequences of S. imbricatus cluster together but the clade is unsupported. Hydnellum and Sarcodon are recovered as sister clades but the support for this arrangement is weak.

For target taxa the ML tree is essentially similar to the BI tree with strong support for the similarly composed Hydnellum and Sarcodon clades (Fig. 2). As for the BI analysis the relationships among species within Hydnellum and Sarcodon are not resolved except for a weak to moderate support for grouping H. aurantiacum with H. auratile and H. suaveolens with S. versipellis. S. fuligineoviolaceus, S. glaucopus, and S. joeides also group together in the ML tree but without support. Again S. imbricatus does not get support and is not separated from S. quercinofibulatus.

The aligned ITS dataset consisted of 1068 nucleotide positions of which 505 remained for the analyses after removal of ambiguous regions. Bayesian inference produced a tree with two strongly supported clades (Fig. 3). The smaller one, which we here informally call “Neosarcodon”, contains nine Sarcodon species, all with a distribution in the tropical and subtropical Americas. Remaining Hydnellum and Sarcodon taxa, including both type species, formed the other clade. Within the latter clade two subclades are visible, corresponding to the genera Hydnellum and Sarcodon, and with the same delimitation as in the LSU trees. Only the Sarcodon subclade has strong support. Within each larger clade several groups of taxa received moderate to strong support. The reader is referred to Fig. 2 for further details.

Figure 2. 

Maximum likelihood analyses of LSU dataset for Thelephorales. Branches in bold have a posterior probability value of 1 in Bayesian inference and 100% bootstrap support in ML analysis, if not otherwise indicated by a figure. Lower support values on other branches are indicated by figures. Steccherinum ochraceum and Sistotrema brinkmannii are used as outgroup (branch lengths shortened).

The ML tree recovered the same two main clades with strong support but could not resolve the relationships within the larger Hydnellum/Sarcodon clade. In the ML tree the clade corresponding to Hydnellum in the LSU tree is correctly identified but not supported while the clade corresponding to Sarcodon appears polyphyletic.

Based on these results we hereby revise the limits of the two genera by moving a number of species from Sarcodon to Hydnellum. Consequently the genus description for Hydnellum must be emended while the genus description for Sarcodon can remain unaltered.

Taxonomy

Hydnellum P.Karst., Meddn Soc. Fauna Flora fenn. 5: 41 (1879).

Type species

Hydnellum suaveolens (Scop.:Fr.) P.Karst. (1879)

Basionym

Hydnum suaveolens Scop.:Fr. (1772)

Basidiomata with pileus and stipe, single or concrescent; pileus thin to thick, at first smooth and velutinous, when mature felted, fibrillose, scaly, ridged, or irregularly pitted and scrupose, mostly brownish but also with white, olive yellowish, orange, purplish or bluish colours, often concentrically zonate; stipe narrow to thick, solid, mostly short; hymenophore hydnoid, usually strongly decurrent; context from soft and brittle to corky or woody; hyphal system monomitic, septa with or without clamps, context hyphae inflated or not; cystidia lacking; basidia narrowly clavate, producing four sterigmata; basidiospores with irregular outline, more or less lobed, verrucose, brownish. Terrestrial, forming ectomycorrhiza with forest trees.

Hydnellum amygdaliolens (Rubio Casas, Rubio Roldán & Català) E.Larss., K.H.Larss. & Kõljalg, comb. nov.

MycoBank No: 830570

Basionym

Sarcodon amygdaliolens Rubio Casas, Rubio Roldán & Català, Boln Soc. Micol. Madrid 35: 44−45. 2011. Holotype: Spain, Tamajón, Barranco la Jara. L. Rubio-Casas & L. Rubio-Roldán, AH 42113.

Hydnellum fennicum (P.Karst.) E.Larss., K.H.Larss. & Kõljalg, comb. nov.

MycoBank No: 830571

Basionym

Sarcodon scabrosus var. fennicus P.Karst., Bidr. Känn. Finl. Nat. Folk 37: 104. 1882. Type: not indicated (neotype: H, designated by Maas Geesteranus & Nannfeldt 1969: 406)

Hydnellum fuligineoviolaceum (Kalchbr.) E.Larss., K.H.Larss. & Kõljalg, comb. nov.

MycoBank No: 830572

Basionym

Hydnum fuligineoviolaceum Kalchbr., in Fries, Hymenomyc. eur. (Upsaliae): 602. 1874. Holotype: Slovakia, Presovsky kraj, Olaszi. C. Kalchbrenner, UPS F-173546.

Hydnellum fuscoindicum (K.A.Harrison) E.Larss., K.H.Larss. & Kõljalg, comb. nov.

MycoBank No: 830573

Basionym

Hydnum fuscoindicum K.A.Harrison, Can. J. Bot. 42: 1213. 1964. Holotype: USA, Washington, Olympic Nat. Park, A.H. Smith. MICH 10847.

Hydnellum glaucopus (Maas Geest. & Nannf.) E.Larss., K.H.Larss. & Kõljalg, comb. nov.

MycoBank No: 830574

Basionym

Sarcodon glaucopus Maas Geest. & Nannf., Svensk bot. Tidskr. 63: 407. 1969. Holotype: Sweden, Uppland, Börje par., J. Eriksson. UPS F-013955.

Hydnellum joeides (Pass.) E.Larss., K.H.Larss. & Kõljalg, comb. nov.

MycoBank No: 830575

Basionym

Hydnum joeides Pass., Nuovo G. bot. ital. 4: 157. 1872. Holotype: Italy, Emilia-Romagna, Collecchio, G. Passerini. PAD.

Hydnellum lepidum (Maas Geest.) E. Larss., K.H.Larss. & Kõljalg, comb. nov.

MycoBank No: 830576

Basionym

Sarcodon lepidus Maas Geest., Verh. K. ned. Akad. Wet., tweede sect. 65: 105. 1975. Holotype: The Netherlands, Lochem, Ampsen, G. & H. Piepenbroek. L.

Hydnellum lundellii (Maas Geest. & Nannf.) E.Larss., K.H.Larss. & Kõljalg, comb. nov.

MycoBank No: 830577

Basionym

Sarcodon lundellii Maas Geest. & Nannf., Svensk bot. Tidskr. 63: 421. 1969. Type: Sweden, Uppland, Storvreta, S. Lundell & J.A. Nannfeldt, distributed in S. Lundell & J.A. Nannfeldt Fungi exs. suec. as number 252 (lectotype, designated here, UPS F-010975; MycoBank No.: MBT387081). The UPS herbarium has two copies of the exsiccate and the specimens of H. lundellii are registered as F-010975 and F-013956, respectively. From F-010975 an ITS2 sequence has been generated [GenBank MK753037] and this specimen is here selected as lectotype).

Hydnellum martioflavum (Snell, K.A.Harrison & H.A.C.Jacks.) E.Larss., K.H.Larss. & Kõljalg, comb. nov.

MycoBank No: 830578

Basionym

Hydnum martioflavum Snell, K.A.Harrison & H.A.C.Jacks., Lloydia 25: 161. 1962. Holotype: Canada, Quebec, Ste Anne de la Pocatière, H.A.C. Jackson & W.H. Snell 13 Sep. 1954, BPI 259438.

Hydnellum scabrosum (Fr.) E.Larss., K.H.Larss. & Kõljalg, comb. nov.

MycoBank No: 830579

Basionym

Hydnum scabrosum Fr., Anteckn. Sver. Ätl. Svamp.: 62. 1836. Type: not indicated (neotype: Sweden, Småland, Femsjö, S. Lundell, UPS F-013954, designated by Maas Geesteranus & Nannfeldt 1969: 426)

Hydnellum underwoodii (Banker) E.Larss., K.H.Larss. & Kõljalg, comb. nov.

MycoBank No: 830580

Basionym

Sarcodon underwoodii Banker, Mem. Torrey bot. Club 12: 147. 1906. Holotype: USA, Connecticut, NY 776131.

Hydnellum versipelle (Fr.) E.Larss., K.H.Larss. & Kõljalg, comb. nov.

MycoBank No: 830581

Basionym

Hydnum versipelle Fr., Öfvers. K. Svensk. Vetensk.-Akad. Förhandl. 18(1): 31. 1861. Type: not indicated (neotype: Sweden, Uppland, Danmark par., J. Eriksson & H. Nilsson, UPS F-013958, designated by Maas Geesteranus & Nannfeldt 1969: 430)

Sarcodon Quél. ex P.Karst., Revue mycol., Toulouse 3 (no. 9): 20 (1881).

Type species

Sarcodon imbricatus (L.:Fr.) P.Karst. (1881)

Basionym

Hydnum imbricatum L.:Fr. (1753).

Basidiomata with pileus and stipe, single or concrescent; pileus thin to thick, at first smooth and velutinous, when mature smooth or scaly, brownish; stipe thick, solid, mostly short; hymenophore hydnoid, usually strongly decurrent; context soft and brittle; hyphal system monomitic, septa with clamps, context hyphae inflated; cystidia lacking; basidia narrowly clavate, producing four sterigmata; basidiospores with irregular outline, more or less lobed, verrucose, brownish. Terrestrial, forming ectomycorrhiza with forest trees.

Discussion

In this paper we show that the current morphology-based concepts of Sarcodon and Hydnellum do not correspond to monophyletic subgroups within the Thelephorales. The characters traditionally used to separate the two genera do not reflect true relationships. These characters, however, are vague and open to subjectivity; hence it is not surprising that they have now been shown to be unreliable. Maas Geesteranus (1975) pointed to the context structure and consistency as the main differentiating character. For Hydnellum he describes the context as “... fibrillose, soft or tough, corky to woody, more or less duplex, zoned, ...” and hyphae are said to be “...usually not inflating ...”. In Sarcodon the same structures are described as “... fleshy, brittle, soft or firm (never corky or woody), not duplex, not zoned ...” and “...hyphae inflating ...”. While these morphological characteristics remain true for Sarcodon, the corresponding descriptions for Hydnellum had to be emended.

Instead of context structure it seems that average basidiospore size may in most cases offer a possibility to separate a Sarcodon species from one belonging to Hydnellum. Table 2 summarizes basidiospore measurements from the literature. Average basidiospore lengths in Hydnellum fall between 4.45 and 6.95 µm while the same figures for Sarcodon are 7.4 and 9 µm, ornamentation excluded. However, S. quercinofibulatus clearly deviates from this pattern. According to measurements in the protologue (Pérez-de-Gregorio et al. 2011) and in Vizzini et al. (2013) average basidiospore length was measured to 6.95 and 7.0, respectively, but then included the ornamentation. Measurements excluding ornamentation would be approximately 1 µm less. Clearly, for S. quercinofibulatus basidiospore length alone will not be decisive for genus placement.

Basidiospore measurements for Hydnellum and Sarcodon from the literature. Sources: B = Baird et al. (2013), M = Maas Geesteranus (1975), J = Johannesson et al. (1999). All measurements exclude ornamentation. For species treated in this paper names follow our new classification. For other species names are according to cited authors.

Species Measurements Mean length
Hydnellum aurantiacum (M) (5.8−)6−6.7 × (4−)4.3−4.9 6.35
Hydnellum auratile (M) 4.9−5.8 × 3.6−4.5 5.35
Hydnellum caeruleum (M) 5.4−6(−6.3) × 3.4−4.3 5.70
Hydnellum compactum (Pers.:Fr.) P.Karst. (M) 5.4−6.3 × 3.6−4.5 5.85
Hydnellum complicatum (B) 4−5 × 3−5 4.50
Hydnellum concrescens (M) 5.4−6.1 × (3.6−)4−4.5 5.75
Hydnellum cristatum (B) 5−6 × 4−5 5.50
Hydnellum cruentum K.A.Harrison (B) 4−5 × 3−4 4.50
Hydnellum cumulatum (M) 4.3−5.6 × 3.6−4.3 4,95
Hydnellum diabolus (B) 6−7 × 5−6 6.50
Hydnellum earlianum (B) 5−6 × 4−5 5.50
Hydnellum fennicum (M) 6.3−7.6 × 4.5−5.2 6.95
Hydnellum ferrugineum (M) (5.4−)5.8−6.3 × 3.6−4.5 6.05
Hydnellum ferrugipes (B) 5−7 × 5−6 6.00
Hydnellum fuligineoviolaceum (M) 5.4−6.5 × 4−4.7(−5.4) 5.95
Hydnellum geogenium (M) 4.5−5.2 × 3.1−3.6 4.85
Hydnellum glaucopus (M) (5−)5.4−5.8(−6.3) × (3.6−)4−4.5 5.60
Hydnellum gracilipes (M) 4.3−4.6 × 2.7−3.6 4.45
Hydnellum joeides (M) 5.4−5.8 × 3.6−4.2 5.60
Hydnellum lepidum (M) 5.8−6.3 × 3.6−4.3 6.05
Hydnellum lundellii (M) 4.9−5.8 × 3.6−4.2 5.35
Hydnellum martioflavum (M) 5−6.3 × 3.6−4.5 5.65
Hydnellum peckii (M) 4.9−5.4 × 3.8−4 5.15
Hydnellum pineticola (B) 5−7 × 4−6 6.00
Hydnellum piperatum (B) 4−6 × 4−5 5.00
Hydnellum scabrosum (M) (5.4−)6.3−7.3 × (3.6−)4−5 6.80
Hydnellum scleropodium (B) 4−6 × 3−4 5.00
Hydnellum spongiosipes (B) 6−7 × 5−6 6.50
Hydnellum suaveolens (M) 4−5 × 3−3.6 4.50
Hydnellum subsuccosum (B) 5−6 × 4−6 5.50
Hydnellum versipelle (M) 4.5−5.5 × 3.5−4.5 5.00
Hydnellum underwoodii (B) 5−7 × 5−6 6.00
Sarcodon atroviridis (B) 8−9 × 7−8 8.50
Sarcodon excentricus R.E.Baird (B) 8−9 × 6−8 8.50
Sarcodon harrisonii R.E.Baird (B) 7−9 × 6−8 8.00
Sarcodon leucopus (M) (6.7−)7.2−7.6(−9) × 4.5−5.6 7.40
Sarcodon imbricatus (M) 7.2−8.2 × 4.9−5.4 7.70
Sarcodon scabripes (B) 8−10 × 7−9 9.00
Sarcodon squamosus (J) 7.2−8.2 × 4.9−5.4 7.70

Not all sequences from species described as Sarcodon spp. were recovered within either Sarcodon or Hydnellum. In our ITS-only analyses nine species formed a well-supported clade of their own, separated from Sarcodon sensu stricto and Hydnellum (Fig. 3). This clade, here informally called “Neosarcodon”, contains species collected in tropical and subtropical regions of the Western Hemisphere and may represent one or several distinct genera. However, further analyses based on an expanded dataset using more conservative molecular markers would be required to definitely identify any new higher taxa in the group.

Figure 3. 

Ultrametric default rooted BEAST tree of ITS dataset for Hydnellum and Sarcodon. Posterior probability values and bootstrap percent support from ML analysis are indicated by figures; na = not applicable.

The failure to generate support for Sarcodon and Hydnellum in the ITS-only analyses reflects the large genetical distances present among the species within this marker. Our general experience with the ITS region for thelephoralean target genera is that species are extremely well separated and the internal variation surprisingly low, even when a large number of specimens from both Europe and America are considered. On the other hand, the genetical difference among species is moderate to high, making alignments difficult and prone to ambiguities. In our ITS analyses we chose to remove ambiguous regions, thus halving the number of nucleotide positions suggested by automatic alignment through MAFFT. This seems to have affected the ML analyses most. However, the ITS analyses only served to position neotropical Sarcodon species and the results clearly show that they belong to a separate lineage.

Otto (1997) suggested that Hydnum auratile is a later synonym of Hydnum aurantiacum and that the species we now call Hydnellum aurantiacum should be named Hydnellum floriforme (Schaeff.) Banker. The name change is based on a reinterpretation of Batsch’s original illustration, which, according to Otto, clearly shows the same species as Hydnum auratile. In phylogenetic analyses H. aurantiacum and H. auratile are sister taxa and during our study we have sequenced several specimens identified as H. auratile that turned out to be H. aurantiacum. Thus separating these species can be hazardous and to interpret illustrations must be even harder. We currently do not accept this unfortunate name change.

The present study will serve as the basis for further exploration of species limits within Hydnellum and Sarcodon. As has been demonstrated for the genera, many species interpretations are in need of revision. Over the years we have found numerous specimen misidentifications as well as specimens that could not be assigned to pre-existing names. A closer inspection of the ITS tree in Fig. 3, where we let the terminals retain the identifications given in GenBank, shows some examples. The American sequence of Sarcodon joeides (KC571772) does not cluster with the European representative of the same species (MK602751) and the American sequence named Hydnellum earlianum seems to be identical to what is in Europe called H. auratile. Considering that many stipitate hydnoid species are red-listed and used as indicators of forests in need of conservation (Ainsworth 2005, Nitare 2019), it is of utmost importance to sort out the taxonomy of these species.

Acknowledgements

This study was supported by grants from ArtsDatabanken, Norway, to KH Larsson (ADB54-09), from Artdatabanken, Sweden, to E Larsson (2014-152 4.3), and from Estonian Research Council to U Kõljalg (IUT20-30). We also acknowledge support to S Svantesson from Kungliga Vetenskaps- och Vitterhetssamhället i Göteborg and from Kapten Carl Stenholms donatationsfond. We are grateful to many dedicated mycologists in Norway, Sweden and Finland for sending valuable collections. We are especially grateful to Johan Nitare for sharing with us his outstanding knowledge of stipitate hydnoid fungi and for duplicates from his herbarium. We also thank Martyn Ainsworth and Terry Henkel whose thorough reviews improved this paper considerably.

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