Citation {#SECID0EUAAC}
========

Ji X, Wu D-M, Liu S, Si J, Cui B-K (2019) *Crassisporus* gen. nov. (Polyporaceae, Basidiomycota) evidenced by morphological characters and phylogenetic analyses with descriptions of four new species. MycoKeys 57: 61--84. [https://doi.org/10.3897/mycokeys.57.38035](10.3897/mycokeys.57.38035)

Introduction {#SECID0EBBAC}
============

Polyporales is one of the most diverse orders of Basidiomycota including more than 1800 described species in 216 genera and 13 families ([@B12]). In the last 10 years, many new genera in Polyporales have been established, such as *Datroniella* B.K. Cui, Hai J. Li & Y.C. Dai ([@B15]), *Fragifomes* B.K. Cui, M.L. Han & Y.C. Dai ([@B9]), *Megasporia* B.K. Cui, Y.C. Dai & Hai J. Li ([@B14]), *Pseudofibroporia* Yuan Y. Chen & B.K. Cui ([@B2]), and *Pseudomegasporoporia* X.H.Ji & F.Wu ([@B10]).

During the investigations of species diversity and phylogeny of Polyporales, four new species were found that did not belong to any known genus, for which reason, a new genus is established to accommodate them. Morphologically, these four taxa do not fit any of the known polypore taxa. To confirm the position of the new genus, phylogenetic analyses of the new genus and related taxa within Polyporales were carried out based on the internal transcribed spacer (ITS) regions, the large subunit nuclear ribosomal RNA gene (nLSU), the small subunit mitochondrial rRNA gene sequences (mtSSU), the translation elongation factor 1-α gene (EF1-α), and the second largest subunit of RNA polymerase II (RPB2).

Materials and methods {#SECID0EREAC}
=====================

Morphological studies {#SECID0EVEAC}
---------------------

The studied specimens were deposited at the herbarium of the Institute of Microbiology, Beijing Forestry University (BJFC). Macro-morphological descriptions are based on the field notes and measurements of herbarium specimens. Color terms follow [@B22]. Micro-morphological data were obtained from the dried specimens and observed under a light microscope following [@B29]. Sections were studied at magnifications up to 1000× using a Nikon E80i microscope and phase contrast illumination (Nikon, Tokyo, Japan). Drawings were made with the aid of a drawing tube. Microscopic features, measurements, and drawings were made from slide preparations stained with cotton blue and Melzer's reagent. Spores were measured from sections cut from the tubes. In presenting the variation of spore size, 5% of measurements were excluded from each end of the range, and were given in parentheses. The following abbreviations were used: **KOH**, 5% potassium hydroxide; **IKI**, Melzer's reagent; **IKI-**, neither amyloid nor dextrinoid; **CB**, cotton blue; **CB+**, cyanophilous; **CB-**, acyanophilous; **L**, mean spore length (arithmetic average of all spores); **W**, mean spore width (arithmetic average of all spores); **Q**, variation in the L/W ratios between the specimens studied; ***n*** (a/b), number of spores (a) measured from given number (b) of specimens.

DNA extraction and sequencing {#SECID0EPGAC}
-----------------------------

A CTAB rapid plant genome extraction kit (Aidlab Biotechnologies Co. Ltd, Beijing) was used to extract total genomic DNA from dried specimens, and performed the polymerase chain reaction (**PCR**) according to the manufacturer's instructions with some modifications ([@B1]). The ITS region was amplified with primer pairs ITS5 and ITS4 ([@B33]). The nLSU region was amplified with primer pairs LR0R and LR7 (<http://www.biology.duke.edu/fungi/mycolab/primers.htm>). The mtSSU region was amplified with primer pairs MS1 and MS2 ([@B33]). Part of EF1-α was amplified with primer pairs EF1-983F and EF1-1567R ([@B24]). RPB2 was amplified with primer pairs fRPB2-5F and fRPB2-7cR or bRPB2-6F and bRPB2-7R ([@B17]; [@B19]). The PCR procedure for ITS, mtSSU and EF1-α was as follows: initial denaturation at 95 °C for 3 min, followed by 34 cycles at 94 °C for 40 s, 54 °C for ITS and mtSSU, 54--56 °C for EF1-α for 45 s, 72 °C for 1 min, and a final extension of 72 °C for 10 min. The PCR procedure for nLSU was as follows: initial denaturation at 94 °C for 1 min, followed by 34 cycles at 94 °C for 30 s, 50 °C for 1 min, 72 °C for 1.5 min, and a final extension of 72 °C for 10 min. The PCR procedure for RPB2 was as follows: initial denaturation at 94 °C for 2 min, followed by 10 cycles at 94 °C for 40 s, 60 °C for 40 s and 72 °C for 2 min, then followed by 37 cycles at 94 °C for 45 s, 55--57 °C for 1.5 min and 72 °C for 2 min, and a final extension of 72 °C for 10 min. The PCR products were purified and sequenced at Beijing Genomics Institute, China, with the same primers. All newly generated sequences were submitted to GenBank (Table [1](#T1){ref-type="table"}).

###### 

Species, specimens and GenBank accession numbers of sequences used in this study.

  --------------------------------- ------------------------ -------------------------- -------------------------- -------------------------- -------------------------- ------------------------------ --------------------------
  Species                           Sample no.               Locality                   GenBank accessions                                                                                              
  ITS                               nLSU                     mtSSU                      EF1-α                      RPB2                                                                                 
  *Abortiporus biennis*             EL 65-03                 Sweden                     [JN649325](JN649325)       [JN649325](JN649325)       --                         --                             --
  *Abundisporus fuscopurpureus*     Cui 10950                China                      [KC456254](KC456254)       [KC456256](KC456256)       [KF051025](KF051025)       [KF181154](KF181154)           --
  *A. pubertatis*                   Dai 11310                China                      [KC787568](KC787568)       [KC787575](KC787575)       [KF051031](KF051031)       [KF181125](KF181125)           
  Dai 11927                         China                    [KC787569](KC787569)       [KC787576](KC787576)       [KF051034](KF051034)       [KF181128](KF181128)       --                             
  *A. sclerosetosus*                MUCL 41438               Singapore                  [FJ411101](FJ411101)       [FJ393868](FJ393868)       --                         --                             --
  *A. violaceus*                    Ryvarden 32807           Finland                    [KF018127](KF018127)       [KF018135](KF018135)       [KF051038](KF051038)       [KF181132](KF181132)           --
  *Antrodia albida*                 CBS 308.82               USA                        [DQ491414](DQ491414)       [AY515348](AY515348)       --                         --                             --
  *A. macra*                        MUAF 887                 Czech Republic             [EU340898](EU340898)       --                         --                         --                             --
  *Bjerkandera adusta*              NBRC 4983                Unknown                    [AB733156](AB733156)       [AB733333](AB733333)       --                         --                             --
  *Cinereomyces lindbladii*         KHL 12078                Norway                     [FN907906](FN907906)       [FN907906](FN907906)       --                         --                             --
  *Climacocystis borealis*          KHL 13318                Estonia                    [JQ031126](JQ031126)       [JQ031126](JQ031126)       --                         --                             --
  *Coriolopsis brunneoleuca*        Cui 13911                China                      [MK116480](MK116480) ^a^   [MK116489](MK116489) ^a^   [MK116498](MK116498) ^a^   --                             [MK124544](MK124544) ^a^
  *C. brunneoleuca*                 Dai 12180                China                      [KC867414](KC867414)       [KC867432](KC867432)       --                         --                             [KF274655](KF274655)
  *C. polyzona*                     BKW004                   Ghana                      [JN164978](JN164978)       [JN164790](JN164790)       --                         [JN164881](JN164881)           [JN164856](JN164856)
  *C. retropicta*                   Cui 13849                China                      [MK116481](MK116481) ^a^   [MK116490](MK116490) ^a^   [MK116499](MK116499) ^a^   [MK122979](MK122979) ^a^       [MK124545](MK124545) ^a^
  Cui 14030                         China                    [MK116482](MK116482) ^a^   [MK116491](MK116491) ^a^   [MK116500](MK116500) ^a^   [MK122980](MK122980) ^a^   [MK122987](MK122987) ^a^       
  *Crassisporus imbricatus*         Cui 6556                 China                      [KC867351](KC867351)       [KC867426](KC867426)       --                         --                             --
  *C. imbricatus*                   Dai 10788                China                      [KC867350](KC867350)       [KC867425](KC867425)       [KX838374](KX838374)       --                             --
  *C. leucoporus*                   Cui 16801                Australia                  [MK116488](MK116488) ^a^   [MK116497](MK116497) ^a^   [MK116507](MK116507) ^a^   [MK122986](MK122986) ^a^       [MK122993](MK122993) ^a^
  *C. macroporus*                   Cui 14465                China                      [MK116485](MK116485) ^a^   [MK116494](MK116494) ^a^   [MK116504](MK116504) ^a^   [MK122983](MK122983) ^a^       [MK122990](MK122990) ^a^
  Cui 14468                         China                    [MK116486](MK116486) ^a^   [MK116495](MK116495) ^a^   [MK116505](MK116505) ^a^   [MK122984](MK122984) ^a^   [MK122991](MK122991) ^a^       
  *C. microsporus*                  Cui 16221                China                      [MK116487](MK116487) ^a^   [MK116496](MK116496) ^a^   [MK116506](MK116506) ^a^   [MK122985](MK122985) ^a^       [MK122992](MK122992) ^a^
  *Daedaleopsis confragosa*         Cui 6892                 China                      [KU892428](KU892428)       [KU892448](KU892448)       [KX838381](KX838381)       [KX838418](KX838418)           [KU892507](KU892507)
  *D. hainanensis*                  Cui 5178                 China                      [KU892435](KU892435)       [KU892462](KU892462)       [KX838413](KX838413)       [KX838441](KX838441)           [KU892495](KU892495)
  *Datronia mollis*                 RLG6304sp                USA                        [JN165002](JN165002)       [JN164791](JN164791)       --                         [JN164901](JN164901)           [JN164872](JN164872)
  *Earliella scabrosa*              PR1209                   Puerto Rico                [JN165009](JN165009)       [JN164793](JN164793)       --                         --                             [JN164866](JN164866)
  *Fomes fomentarius*               ES 2008-3                Sweden                     [JX109860](JX109860)       [JX109860](JX109860)       --                         --                             --
  *Fomitella supina*                JV0610                   Guatemala                  [KF274645](KF274645)       [KF274646](KF274646)       --                         --                             --
  *F. supina*                       Ryvarden 39027           Puerto Rico                [KF274643](KF274643)       --                         --                         --                             --
  *Fomitopsis betulina*             Dai 11449                China                      [KR605798](KR605798)       [KR605737](KR605737)       [KR605998](KR605998)       [KR610726](KR610726)           [KR610816](KR610816)
  *F. pinicola*                     Cui 10405                China                      [KC844852](KC844852)       [KC844857](KC844857)       [KR605961](KR605961)       [KR610690](KR610690)           [KR610781](KR610781)
  *Fragiliporia fragilis*           Dai 13080                China                      [KJ734260](KJ734260)       [KJ734264](KJ734264)       --                         --                             --
  *F. fragilis*                     Dai 13559                China                      [KJ734261](KJ734261)       [KJ734265](KJ734265)       --                         --                             --
  Yuan 5516                         China                    [KJ734263](KJ734263)       [KJ734267](KJ734267)       --                         --                         --                             
  *Funalia gallica*                 Dai 10977                China                      [KC867378](KC867378)       [KC867452](KC867452)       --                         --                             [KU182651](KU182651)
  *F. trogii*                       RLG4286Sp                USA                        [JN164993](JN164993)       [JN164808](JN164808)       --                         [JN164898](JN164898)           [JN164867](JN164867)
  *Gelatoporia subvermispora*       BRNU 592909              Czech Republic             [FJ496694](FJ496694)       [FJ496706](FJ496706)       --                         --                             --
  *Grammethelopsis subtropica*      Cui 9035                 China                      [JQ845094](JQ845094)       [JQ845097](JQ845097)       [KF051030](KF051030)       [KF181124](KF181124)           --
  Cui 9041                          China                    [JQ845096](JQ845096)       [JQ845099](JQ845099)       [KF051039](KF051039)       [KF181133](KF181133)       --                             
  *Haploporus latisporus*           Dai 11873                China                      [KU941847](KU941847)       [KU941871](KU941871)       [KU941896](KU941896)       [KU941934](KU941934)           [KU941918](KU941918)
  *H. latisporus*                   Dai 10562                China                      [KU941848](KU941848)       [KU941872](KU941872)       [KU941897](KU941897)       [KU941935](KU941935)           [KU941919](KU941919)
  *H. odorus*                       Yuan 2365                China                      [KU941846](KU941846)       [KU941870](KU941870)       [KU941895](KU941895)       [KU941933](KU941933)           [KU941917](KU941917)
  Dai 11296                         China                    [KU941845](KU941845)       [KU941869](KU941869)       [KU941894](KU941894)       [KU941932](KU941932)       [KU941916](KU941916)           
  *H. subtrameteus*                 Dai 4222                 China                      [KU941849](KU941849)       [KU941873](KU941873)       [KU941898](KU941898)       [KU941936](KU941936)           [KU941920](KU941920)
  Cui 10656                         China                    [KU941850](KU941850)       [KU941874](KU941874)       [KU941899](KU941899)       [KU941937](KU941937)       [KU941921](KU941921)           
  *Heterobasidion annosum*          PFC 5327                 Greece                     [KC492915](KC492915)       --                         --                         [KC571655](KC571655)           --
  *Hexagonia apiaria*               Cui 6447                 China                      [KC867362](KC867362)       [KC867481](KC867481)       [MG847228](MG847228)       [MG867697](MG867697)           [KF274660](KF274660)
  *H. apiaria*                      Dai 10784                China                      [KX900635](KX900635)       [KX900682](KX900682)       [KX900732](KX900732)       [KX900822](KX900822)           [MG867677](MG867677)
  *H. hirta*                        Dai 5081                 China                      --                         [KC867486](KC867486)       --                         --                             --
  Cui 4051                          China                    [KC867359](KC867359)       [KC867471](KC867471)       --                         --                         --                             
  *Hornodermoporus latissimus*      Cui 6625                 China                      [HQ876604](HQ876604)       [JF706340](JF706340)       [KF051040](KF051040)       [KF181134](KF181134)           --
  Dai 12054                         China                    [KX900639](KX900639)       [KX900686](KX900686)       [KF218297](KF218297)       [KF286303](KF286303)       --                             
  *H. martius*                      MUCL 41677               Argentina                  [FJ411092](FJ411092)       [FJ393859](FJ393859)       --                         --                             --
  MUCL 41678                        Argentina                [FJ411093](FJ411093)       [FJ393860](FJ393860)       --                         --                         --                             
  *Hydnopolyporus fimbriatus*       LR 40855                 Puerto Rico                [JN649347](JN649347)       [JN649347](JN649347)       --                         --                             --
  *Hypochnicium lyndoniae*          NL 041031                UK                         [JX124704](JX124704)       [JX124704](JX124704)       --                         --                             --
  *Laetiporus montanus*             Cui 10011                China                      [KF951274](KF951274)       [KF951315](KF951315)       [KX354570](KX354570)       [KX354617](KX354617)           [KT894790](KT894790)
  *L. sulphureus*                   Cui 12388                China                      [KR187105](KR187105)       [KX354486](KX354486)       [KX354560](KX354560)       [KX354607](KX354607)           [KX354652](KX354652)
  *Lenzites betulina*               HHB9942Sp                USA                        [JN164983](JN164983)       [JN164794](JN164794)       --                         [JN164895](JN164895)           [JN164860](JN164860)
  *Megasporia ellipsoidea*          Cui 13854                China                      [MK116483](MK116483) ^a^   [MK116492](MK116492) ^a^   [MK116501](MK116501) ^a^   [MK122981](MK122981) ^a^       [MK122988](MK122988) ^a^
  *M. major*                        Cui 10253                China                      [JQ314366](JQ314366)       [JQ780437](JQ780437)       [MK116502](MK116502) ^a^   --                             --
  *Megasporoporiella rhododendri*   Cui 10745                China                      [MK116484](MK116484) ^a^   [MK116493](MK116493) ^a^   [MK116503](MK116503) ^a^   [MK122982](MK122982)22982^a^   [MK122989](MK122989) ^a^
  *M. subcavernulosa*               Cui 14247                China                      [MG847213](MG847213)       [MG847222](MG847222)       [MG847234](MG847234)       [MG867705](MG867705)           [MG867685](MG867685)
  *Microporus affinis*              Cui 7714                 China                      [JX569739](JX569739)       [JX569746](JX569746)       [KX880696](KX880696)       --                             [KF274661](KF274661)
  *M. vernicipes*                   Dai 9283                 China                      [KX880618](KX880618)       [KX880658](KX880658)       [KX880701](KX880701)       [KX880926](KX880926)           --
  *M. xanthopus*                    Cui 8284                 China                      [JX290074](JX290074)       [JX290071](JX290071)       [KX880703](KX880703)       [KX880878](KX880878)           [JX559313](JX559313)
  *Neodatronia sinensis*            Dai 11921                China                      [JX559272](JX559272)       [JX559283](JX559283)       --                         --                             [JX559320](JX559320)
  *Neofomitella fumosipora*         Cui 8816                 China                      [JX569734](JX569734)       [JX569741](JX569741)       [KX900766](KX900766)       --                             --
  Cui 13581a                        China                    [KX900664](KX900664)       [KX900714](KX900714)       [KX900767](KX900767)       [KX900848](KX900848)       [KX900815](KX900815)           
  *N. rhodophaea*                   TFRI 414                 Unknown                    [EU232216](EU232216)       [EU232300](EU232300)       --                         --                             --
  *Obba rivulosa*                   KCTC 6892                Canada                     [FJ496693](FJ496693)       [FJ496710](FJ496710)       --                         --                             --
  *Perenniporia hainaniana*         Cui 6364                 China                      [JQ861743](JQ861743)       [JQ861759](JQ861759)       [KF051044](KF051044)       [KF181138](KF181138)           --
  *P. hainaniana*                   Cui 6365                 China                      [JQ861744](JQ861744)       [JQ861760](JQ861760)       [KF051045](KF051045)       [KF181139](KF181139)           --
  *P. medulla-panis*                MUCL 49581               Poland                     [FJ411088](FJ411088)       [FJ393876](FJ393876)       --                         --                             --
  Cui 14515                         China                    [MG847214](MG847214)       [MG847223](MG847223)       --                         [MG867707](MG867707)       [MG867687](MG867687)           
  *P. substraminea*                 Cui 10177                China                      [JQ001852](JQ001852)       [JQ001844](JQ001844)       [KF051046](KF051046)       [KF181140](KF181140)           --
  Cui 10191                         China                    [JQ001853](JQ001853)       [JQ001845](JQ001845)       [KF051047](KF051047)       [KF181141](KF181141)       --                             
  *Perenniporiella chaquenia*       MUCL 47648               Argentina                  [FJ411084](FJ411084)       [FJ393856](FJ393856)       --                         [HM467610](HM467610)           --
  *P. micropora*                    MUCL 43581               Cuba                       [FJ411086](FJ411086)       [FJ393858](FJ393858)       --                         [HM467608](HM467608)           --
  *P. neofulva*                     MUCL 45091               Cuba                       [FJ411080](FJ411080)       [FJ393852](FJ393852)       --                         [HM467599](HM467599)           --
  *P. pendula*                      MUCL 46034               Cuba                       [FJ411081](FJ411081)       [FJ393853](FJ393853)       --                         [HM467601](HM467601)           --
  *Phanerochaete chrysosporium*     BKM-F-1767               USSR                       [HQ188436](HQ188436)       [GQ470643](GQ470643)       --                         --                             --
  *Phlebia unica*                   KHL 11786                Sweden                     [EU118657](EU118657)       [EU118657](EU118657)       --                         --                             --
  *Pycnoporus cinnabarinus*         Dai 14386                China                      [KX880629](KX880629)       [KX880667](KX880667)       [KX880712](KX880712)       [KX880885](KX880885)           [KX880854](KX880854)
  *Skeletocutis amorpha*            Miettinen 11038          Finland                    [FN907913](FN907913)       [FN907913](FN907913)       --                         --                             --
  *Stereum hirsutum*                NBRC 6520                Unknown                    [AB733150](AB733150)       [AB733325](AB733325)       --                         --                             --
  *Trametes conchifer*              [FP106793](FP106793)Sp   USA                        [JN164924](JN164924)       [JN164797](JN164797)       --                         [JN164887](JN164887)           [JN164849](JN164849)
  *T. pubescens*                    [FP101414](FP101414)Sp   USA                        [JN164963](JN164963)       [JN164811](JN164811)       --                         [JN164889](JN164889)           [JN164851](JN164851)
  *T. tephroleuca*                  Cui 7987                 China                      [KC848293](KC848293)       [KC848378](KC848378)       [KX880755](KX880755)       [KX880934](KX880934)           [KX880869](KX880869)
  *T. versicolor*                   [FP135156](FP135156)Sp   USA                        [JN164919](JN164919)       [JN164809](JN164809)       --                         [JN164878](JN164878)           [JN164850](JN164850)
  *Truncospora detrita*             MUCL 42649               French Guyana              [FJ411099](FJ411099)       [FJ393866](FJ393866)       --                         --                             --
  *T. macrospora*                   Cui 8106                 China                      [JX941573](JX941573)       [JX941596](JX941596)       [KX880763](KX880763)       [KX880920](KX880920)           [KX880871](KX880871)
  Yuan 3777                         China                    [JX941574](JX941574)       [JX941597](JX941597)       --                         --                         --                             
  *T. ochroleuca*                   MUCL 39726               China Taiwan               [FJ411098](FJ411098)       [FJ393865](FJ393865)       --                         --                             --
  Cui 5671                          China                    [JX941584](JX941584)       [JX941602](JX941602)       [KF218309](KF218309)       [KF286315](KF286315)       --                             
  *T. ohiensis*                     MUCL 41036               USA                        [FJ411096](FJ411096)       [FJ393863](FJ393863)       --                         --                             --
  *Tyromyces chioneus*              Cui 10225                China                      [KF698756](KF698756)       [KF698745](KF698745)       --                         --                             --
  *T. kmetii*                       Penttilä 13474           China                      [KF705040](KF705040)       [KF705041](KF705041)       --                         --                             --
  *Vanderbylia fraxinea*            DP 83                    Italy                      [AM269789](AM269789)       [AM269853](AM269853)       --                         --                             --
  MUCL 39326                        France                   [FJ411094](FJ411094)       [FJ393861](FJ393861)       --                         --                         --                             
  *V. robiniophila*                 Cui 5644                 China                      [HQ876609](HQ876609)       [JF706342](JF706342)       [KF051051](KF051051)       [KF181145](KF181145)           [MG867691](MG867691)
  Cui 7144                          China                    [HQ876608](HQ876608)       [JF706341](JF706341)       [KF051052](KF051052)       [KF181146](KF181146)       --                             
  *V. vicina*                       MUCL 44779               Ethiopia                   [FJ411095](FJ411095)       [FJ393862](FJ393862)       --                         --                             --
  *Whitfordia scopulosa*            Dai 10739                China                      [KC867364](KC867364)       [KC867482](KC867482)       [KX880766](KX880766)       [KX880922](KX880922)           [MG867692](MG867692)
  --------------------------------- ------------------------ -------------------------- -------------------------- -------------------------- -------------------------- ------------------------------ --------------------------

^a^ Newly generated sequences for this study

Phylogenetic analyses {#SECID0EJPAI}
---------------------

Sequences used for phylogenetic analyses in this study are listed in Table [1](#T1){ref-type="table"}. Sequences of ITS, nLSU, mtSSU, EF1-α, and RPB2 were aligned initially in MAFFT 7 ([@B11]; <http://mafft.cbrc.jp/alignment/server/>) and then manually adjusted in BioEdit ([@B8]). Finally, these gene fragments were concatenated with Mesquite 3.2 ([@B18]) for further phylogenetic analyses. Phylogenies were inferred from the combined 2-gene dataset (ITS+nLSU) and 5-gene dataset (ITS+nLSU+mtSSU+EF1-α+RPB2). *Heterobasidion annosum* (Fr.) Bref. and *Stereum hirsutum* (Willd.) Pers. obtained from GenBank were used as outgroups to root trees in the 2-gene based analysis. *Laetiporus montanus* Černý ex Tomšovský & Jankovský and *L. sulphureus* (Bull.) Murrill were selected as outgroups to root trees in the 5-gene based analysis. The final concatenated sequence alignments were deposited in TreeBase (<https://treebase.org/treebase-web/home.html>; submission ID 23521).

Phylogenetic analyses used in this study followed the approach of [@B38] and [@B30]. Maximum parsimony (**MP**) analysis was performed in PAUP\* v. 4.0b10 ([@B32]). All characters were equally weighted and gaps were treated as missing data. Trees were inferred using the heuristic search option with TBR branch swapping and 1000 random sequence additions. Max-trees were set to 5000, branches of zero length were collapsed, and all parsimonious trees were saved. Clade robustness was assessed using a bootstrap (**BT**) analysis with 1000 replicates ([@B6]). Descriptive tree statistics tree length (**TL**), consistency index (**CI**), retention index (**RI**), rescaled consistency index (**RC**) and homoplasy index (**HI**) were calculated for each maximum parsimonious tree generated.

RAxML v. 7.2.6 ([@B31]) was used to perform maximum likelihood (ML) analysis involved 200 ML searches under the GTR+GAMMA model and only the best tree from all searches was kept. In addition, 200 rapid bootstrap replicates were run with the GTR+CAT model to assess the reliability of the nodes.

MrModeltest v. 2.3 ([@B23]; [@B21]) was used to determine the best fit evolution model for the combined multi-gene dataset for Bayesian inference (BI). Bayesian inference was calculated with MrBayes v. 3.1.2 with a general time reversible (GTR) model of DNA substitution and a gamma distribution rate variation across sites ([@B26]). Four Markov chains were run for two runs from random starting trees for 2 million generations (ITS+nLSU), for 5 million generations (ITS+nLSU+mtSSU+EF1-α+RPB2) until the split deviation frequency value \<0.01, and trees were sampled every 100 generation. The first quarter generations were discarded as burn-in. A majority rule consensus tree of all remaining trees was calculated.

Phylogenetic trees were viewed using FigTree v. 1.4.2 (<http://tree.bio.ed.ac.uk/software/figtree/>). Branches that received bootstrap support for maximum parsimony (MP), maximum likelihood (ML) and Bayesian posterior probabilities (BPP) greater than or equal to 75% (MP and ML) and 0.95 (BPP) were considered as significantly supported, respectively.

Results {#SECID0ERXAI}
=======

Molecular phylogeny {#SECID0EVXAI}
-------------------

The combined 2-gene dataset included sequences from 68 fungal samples representing 59 taxa. The dataset had an aligned length of 2111 characters, of which 1249 characters were constant, 196 were variable and parsimony-uninformative, and 666 were parsimony-informative. MP analysis yielded 37 equally parsimonious trees (TL = 4143, CI = 0.345, RI = 0.617, RC = 0.213, HI = 0.655). Best model for the combined 2-gene dataset estimated and applied in the BI was GTR+I+G, lset nst = 6, rates = invgamma; prset statefreqpr = dirichlet (1,1,1,1). MP, ML and BI analyses yielded similar tree topologies with an average standard deviation of split frequencies = 0.006293 (BI), and the ML topology is shown in Figure [1](#F1){ref-type="fig"}. The phylogeny (Fig. [1](#F1){ref-type="fig"}) inferred from the combined ITS+nLSU sequences demonstrated seven major clades for 59 species of the Polyporales. The new genus *Crassisporus* embed in the core polyporoid clade and grouped with *Haploporus* Bondartsev & Singer.

![Phylogeny of *Crassisporus* and related genera in Polyporales based on combined ITS and nLSU sequences. Topology is from ML analysis with parsimony bootstrap support values (≥50 %), maximum likelihood bootstrap support values (≥50 %) and Bayesian posterior probability values (≥0.95).](mycokeys-57-061-g001){#F1}

The combined 5-gene (ITS, nLSU, mtSSU, EF1-α, RPB2) dataset included sequences of 82 fungal samples representing 57 taxa. The dataset had an aligned length of 4306 characters, of which 2521 characters were constant, 258 were variable and parsimony-uninformative, and 1527 were parsimony-informative. MP analysis yielded 1 equally parsimonious tree (TL = 8989, CI = 0.339, RI = 0.620, RC = 0.210, HI = 0.661). Bayesian and ML analyses resulted in a similar topology as the MP analysis, with an average standard deviation of split frequencies = 0.006328 (BI); and the ML topology is shown in Figure [2](#F2){ref-type="fig"}. A further phylogeny (Fig. [2](#F2){ref-type="fig"}) inferred from the combined 5-gene dataset was obtained for more representative taxa in the Polyporaceae and showed that the new genus grouped with *Haploporus* clade but distinctly formed a monophyletic lineage.

![Phylogeny of *Crassisporus* and related species obtained for more representative taxa in the Polyporaceae based on combined sequences dataset of ITS+nLSU+mtSSU+EF1-α+RPB2. Topology is from ML analysis with parsimony bootstrap support values (≥50 %), maximum likelihood bootstrap support values (≥50 %), and Bayesian posterior probability values (≥0.95).](mycokeys-57-061-g002){#F2}

Taxonomy {#SECID0EP6AI}
========

Crassisporus
------------

Fungi

Polyporales

Polyporaceae

B.K. Cui & Xing Ji gen. nov.

B960EFA709CE585D9A1A3C7143619ACB

828486

### Notes.

Differs from other genera by the combination of effused-reflexed to pileate basidiocarps, pale yellowish brown to yellowish brown, concentrically zonate or sulcate, velutinate pileal surface, a trimitic hyphal system with clamped generative hyphae, tissues darkening in KOH, and oblong to broadly ellipsoid, hyaline, smooth and slightly thick-walled basidiospores.

### Etymology.

*Crassisporus* (Lat.): referring to thick-walled basidiospores.

### Type species.

*Crassisporus macroporus* B.K. Cui & Xing Ji.

Basidiocarps annual, effused-reflexed to pileate. Pileal surface pale yellowish brown, yellowish brown to umber-brown when dry, concentrically zonate or sulcate, velutinate. Pore surface usually white, cream buff to cinnamon-buff when fresh, buff, pale yellowish brown to yellowish brown when dry. Context pale yellowish brown to yellowish brown, leathery to corky when dry. Tubes concolorous with the context, corky when dry. Hyphal system trimitic with clamped generative hyphae, skeletal hyphae hyaline to pale yellowish brown, binding hyphae hyaline to pale yellowish brown, negative in Melzer's reagent, tissues turning to black in KOH. Cystidia absent, thin-walled cystidioles usually present. Basidiospores oblong to broadly ellipsoid, hyaline, smooth, slightly thick-walled, IKI-, CB-. Causing a white rot.

Crassisporus imbricatus
-----------------------

Fungi

Polyporales

Polyporaceae

B.K. Cui & Xing Ji sp. nov.

0553B393CCA55E658DE28ECE51DD0D6F

828487

[Figs 3](#F3){ref-type="fig"} [, 4](#F4){ref-type="fig"}

### Notes.

*Crassisporus imbricatus* is characterized by imbricate basidiocarps, pale greyish-brown pore surface when dry, round to angular pores (3--5 per mm), and oblong ellipsoid basidiospores (10--14 × 4.5--6.2 μm).

### Holotype.

CHINA. Hainan Province, Changjiang County, Bawangling Nature Reserve, on dead angiosperm tree, 9 May 2009, Dai 10788 (BJFC).

### Etymology.

*Imbricatus* (Lat.): referring to the imbricate basidiocarps.

### Description.

Fruitbody: Basidiocarps annual, effused-reflexed to pileate, imbricate, soft corky, without odor or taste when fresh, leathery to corky upon drying. Pilei semicircular or elongated, projecting up to 1.5 cm, 3.5 cm wide, and 2.5 mm thick at base. Pileal surface yellowish brown, velutinate, concentrically zonate. Pore surface buff when fresh, becoming pale greyish brown when dry; sterile margin indistinct, pores round to angular, 3--5 per mm; dissepiments slightly thick, entire to slightly lacerate. Context yellowish brown, leathery, up to 2.5 mm thick. Tubes concolorous with context, corky, up to 1.5 mm long.

Hyphal structure: Hyphal system trimitic; generative hyphae bearing clamp connections; skeletal and binding hyphae IKI-, CB-; tissues turning to black in KOH.

Context: Generative hyphae infrequent, hyaline, thin-walled, unbranched, 2--3.5 μm in diam.; skeletal hyphae dominant, hyaline to pale yellowish brown, thick-walled with a narrow lumen to subsolid, rarely branched, straight, interwoven, occasionally simple-septate, 2.5--5.5 μm in diam.; binding hyphae hyaline to pale yellowish brown, thick-walled with a narrow lumen to subsolid, flexuous, frequently branched, interwoven, 1.2--2.5 μm in diam.

Tubes: Generative hyphae infrequent, hyaline, thin-walled, occasionally branched, 1.5--3 μm in diam.; skeletal hyphae dominant, hyaline to pale yellowish brown, thick-walled, occasionally branched, strongly interwoven, rarely simple-septate, 1.5--3.5 μm in diam.; binding hyphae hyaline to pale yellowish brown, thick-walled with a narrow lumen to subsolid, flexuous, frequently branched, interwoven, 1--2 μm in diam. Cystidia and cystidioles absent. Basidia clavate, bearing four sterigmata and a basal clamp connection, 19--32 × 9--12 μm; basidioles dominant, in shape similar to basidia, but distinctly smaller.

Spores: Basidiospores oblong ellipsoid, hyaline, slightly thick-walled, smooth, IKI-, CB-, 10--14(--15) × 4.5--6.2(--6.6) μm, L = 12.33 μm, W = 5.34 μm, Q = 2.27--2.36 (*n* = 60/2).

### Type of rot.

White rot.

### Additional specimen (paratype) examined.

CHINA. Hainan Province, Changjiang County, Bawangling Nature Reserve, on fallen branch of *Pinus latteri*, 10 May 2009, Cui 6556 (BJFC).

![Basidiocarps of *Crassisporus imbricatus*. Scale bar: 2 cm.](mycokeys-57-061-g003){#F3}

![Microscopic structures of *Crassisporus imbricatus* (drawn from the holotype) **A** basidiospores **B** basidia and basidioles **C** hyphae from trama **D** hyphae from context.](mycokeys-57-061-g004){#F4}

Crassisporus leucoporus
-----------------------

Fungi

Polyporales

Polyporaceae

B.K. Cui & Xing Ji sp. nov.

D4DB2FEB8DF3520682423C6FAC93540B

828488

[Figs 5](#F5){ref-type="fig"} [, 6](#F6){ref-type="fig"}

### Notes.

*Crassisporus leucoporus* is characterized by a white pore surface when fresh, round to angular pores (3--4 per mm) and oblong ellipsoid basidiospores (8.4--11.2 × 4.2--5.4 μm).

### Holotype.

AUSTRALIA. Queensland, Cairns, Roadside of Mount Whitfield Park, on fallen angiosperm branch, 18 May 2018, Cui 16801 (BJFC).

### Etymology.

*Leucoporus* (Lat.): referring to the white pore surface when fresh.

### Description.

Fruitbody: Basidiocarps annual, effused-reflexed to pileate, corky, without odor or taste when fresh, soft leathery to corky upon drying. Pilei semicircular or elongated, projecting up to 1.5 cm, 3 cm wide, and 6 mm thick at base. Pileal surface yellowish brown to umber-brown, finely velutinate, concentrically sulcate. Pore surface white when fresh, becoming cream, clay buff to pale yellowish brown when dry; sterile margin distinct, cream to pale yellowish brown, up to 1.5 mm wide; pores round to angular, 3--4 per mm; dissepiments slightly thick, entire. Context pale yellowish brown to fulvous, leathery, up to 3 mm thick. Tubes pale yellowish brown, corky, up to 2.5 mm long.

Hyphal structure: Hyphal system trimitic; generative hyphae bearing clamp connections; skeletal and binding hyphae IKI-, CB-; tissues turning to black in KOH.

Context: Generative hyphae infrequent, hyaline, thin-walled, unbranched, 1.1--2.6 μm in diam.; skeletal hyphae in context dominant, pale yellowish brown, thick-walled with a narrow to wide lumen, unbranched, straight, interwoven, occasionally simple-septate, 1.8--3.9 μm in diam.; binding hyphae hyaline to pale yellowish brown, thick-walled with a narrow lumen to subsolid, flexuous, frequently branched, interwoven, 0.7--2.2 μm in diam.

Tubes: Generative hyphae infrequent, hyaline, thin-walled, occasionally branched, 1--2.8 μm in diam.; skeletal hyphae dominant, hyaline to pale yellowish brown, thick-walled with a narrow to wide lumen, occasionally branched, more or less straight, strongly interwoven, 0.9--3.3 μm in diam.; binding hyphae hyaline to pale yellowish brown, thick-walled with a narrow lumen to subsolid, flexuous, frequently branched, interwoven, 0.8--2.1 μm in diam. Cystidia absent, cystidioles fusoid, sometimes septate at the tips, hyaline, thin-walled, 16.7--28.1 × 5.1--6.3 μm. Basidia clavate, bearing four sterigmata and a basal clamp connection, 18.1--29.2 × 6.4--9.8 μm; basidioles dominant, in shape similar to basidia, but smaller.

Spores: Basidiospores oblong ellipsoid, hyaline, smooth, slightly thick-walled, IKI-, CB-, (7.9--)8.4--11.2(--11.5) × (4--)4.2--5.4(--5.7) μm, L = 9.49 μm, W = 4.79 μm, Q = 1.99 (*n* = 60/1).

### Type of rot.

White rot.

![Basidiocarps of *Crassisporus leucoporus*. Scale bars: 1 cm (**A**); 2 cm (**B**).](mycokeys-57-061-g005){#F5}

![Microscopic structures of *Crassisporus leucoporus* (drawn from the holotype) **A** basidiospores **B** basidia and basidioles **C** cystidioles **D** hyphae from trama **E** hyphae from context.](mycokeys-57-061-g006){#F6}

Crassisporus macroporus
-----------------------

Fungi

Polyporales

Polyporaceae

B.K. Cui & Xing Ji sp. nov.

5A4BB7711CD1574BA88A00B6D8089E07

828489

[Figs 7](#F7){ref-type="fig"} [, 8](#F8){ref-type="fig"}

### Notes.

*Crassisporus macroporus* is characterized by cream-buff to cinnamon-buff colored pore surface with distinct sterile margin when fresh, large pores (2--3 per mm) with thin dissepiments, a trimitic hyphal system with cyanophilous skeletal hyphae, the presence of fusoid cystidioles, and oblong ellipsoid basidiospores (9.5--13.2 × 4--6.2 μm).

### Holotype.

CHINA. Guangxi Autonomous Region, Huanjiang County, Mulun Nature Reserve, on fallen angiosperm branch, 10 July 2017, Cui 14468 (BJFC).

### Etymology.

*Macroporus* (Lat.): referring to the large pores.

### Description.

Fruitbody: Basidiocarps annual, effused-reflexed to pileate, corky to leathery, without odor or taste when fresh, soft leathery upon drying. Pilei flabelliform, semicircular or elongated, projecting up to 1.5 cm, 4 cm wide and 5 mm thick at base; resupinate part up to 7 cm long, 4 cm wide, and 5 mm thick at center. Pileal surface buff to yellowish brown when fresh, becoming yellowish brown upon drying, finely velutinate, concentrically sulcate. Pore surface cream, buff to cinnamon-buff when fresh, becoming buff, pale yellowish brown to yellowish brown when dry; sterile margin distinct, buff to pale yellowish brown, up to 2 mm wide; pores round to angular, 2--3 per mm; dissepiments thin, entire to lacerate. Context yellowish brown to pale yellowish brown, leathery, up to 1.5 mm thick. Tubes pale yellowish brown, corky, up to 2 mm long.

Hyphal structure: Hyphal system trimitic; generative hyphae bearing clamp connections; skeletal and binding hyphae IKI-, CB+; tissues turning to black in KOH.

Context: Generative hyphae infrequent, hyaline, thin-walled, unbranched, 1.5--3.5 μm in diam.; skeletal hyphae dominant, pale yellowish brown, thick-walled with a narrow lumen to subsolid, unbranched, more or less straight, interwoven, occasionally simple-septate, 2--5.5 μm in diam.; binding hyphae hyaline to pale yellowish brown, thick-walled with a narrow lumen to subsolid, flexuous, frequently branched, interwoven, 1--3 μm in diam.

Tubes: Generative hyphae infrequent, hyaline, thin-walled, occasionally branched, 1--2 μm in diam.; skeletal hyphae dominant, hyaline to pale yellowish brown, thick-walled with a narrow lumen to subsolid, occasionally branched, more or less straight, strongly interwoven, 1.5--3 μm in diam.; binding hyphae hyaline to pale yellowish brown, thick-walled with a narrow lumen to subsolid, flexuous, frequently branched, interwoven, 0.8--2 μm in diam. Cystidia absent, cystidioles fusoid, hyaline, thin-walled, 13--20 × 4.5--6 μm. Basidia clavate, bearing four sterigmata and a basal clamp connection, 17--28 × 7--8 μm; basidioles dominant, in shape similar to basidia, but smaller.

Spores: Basidiospores oblong ellipsoid, hyaline, smooth, slightly thick-walled, IKI-, CB-, 9.5--13.2(--14) × 4--6.2(--6.5) μm, L = 11.24 μm, W = 4.96 μm, Q = 2.26--2.31 (*n* = 60/2).

### Type of rot.

White rot.

### Additional specimen (paratype) examined.

CHINA. Guangxi Autonomous Region, Huanjiang County, Mulun Nature Reserve, on dead angiosperm tree, 10 July 2017, Cui 14465 (BJFC).

![Basidiocarps of *Crassisporus macroporus*. Scale bars: 2 cm.](mycokeys-57-061-g007){#F7}

![Microscopic structures of *Crassisporus macroporus* (drawn from the holotype) **A** basidiospores **B** basidia and basidioles **C** cystidioles **D** hyphae from trama **e** hyphae from context.](mycokeys-57-061-g008){#F8}

Crassisporus microsporus
------------------------

Fungi

Polyporales

Polyporaceae

B.K. Cui & Xing Ji sp. nov.

DEEAF27C7EED5ADBB62D47DB3B190481

828514

[Figs 9](#F9){ref-type="fig"} [, 10](#F10){ref-type="fig"}

### Notes.

*Crassisporus microsporus* is characterized by pileate basidiocarps, small pores (5--7 per mm), and small, broadly ellipsoid basidiospores (4--5 × 3--3.7 μm).

### Holotype.

CHINA. Yunnan Province, Ruili, Mori Tropical Rainforest Park, on living angiosperm tree, 17 September 2017, Cui 16221 (BJFC).

### Etymology.

*Microsporus* (Lat.): referring to the small basidiospores.

### Description.

Fruitbody: Basidiocarps annual, pileate, sessile, corky, without odor or taste when fresh, soft leathery to corky upon drying. Pilei semicircular, projecting up to 2 cm, 4 cm wide, and 4.5 mm thick at base. Pileal surface pale yellowish brown to yellowish brown, finely velutinate, concentrically sulcate. Pore surface cream, buff to cinnamon-buff when fresh, buff, pale yellowish brown to yellowish brown when dry; sterile margin distinct, buff, up to 1 mm wide; pores round to angular, 5--7 per mm; dissepiments slightly thick, entire. Context pale yellowish brown to yellowish brown, leathery to corky when dry, up to 1.5 mm thick. Tubes concolorous with context, soft corky to corky, up to 3 mm long.

Hyphal structure: Hyphal system trimitic; generative hyphae bearing clamp connections; skeletal and binding hyphae IKI-, CB-; tissues turning to deep brown in KOH.

Context: Generative hyphae infrequent, hyaline, thin-walled, occasionally branched, 1.2--3.5 μm in diam.; skeletal hyphae dominant, hyaline to pale yellowish brown, thick-walled with a narrow lumen, rarely branched, straight, interwoven, occasionally simple-septate, 2.5--6 μm in diam.; binding hyphae hyaline to pale yellowish brown, thick-walled with a narrow lumen to subsolid, flexuous, frequently branched, interwoven, 0.8--2.5 μm in diam.

Tubes: Generative hyphae infrequent, hyaline, thin-walled, rarely branched, 1.2--3 μm in diam.; skeletal hyphae dominant, hyaline to pale yellowish brown, thick-walled with a narrow lumen to subsolid, moderately branched, more or less straight, strongly interwoven, 1.5--3 μm in diam.; binding hyphae hyaline to pale yellowish brown, thick-walled with a narrow lumen to subsolid, flexuous, frequently branched, interwoven, 0.8--2.5 μm in diam. Cystidia absent, cystidioles fusoid, hyaline, thin-walled, 12.5--18 × 4--5.5 μm. Basidia clavate, bearing four sterigmata and a basal clamp connection, 14--21 × 4.5--6 μm; basidioles in shape similar to basidia, but distinctly smaller.

Spores: Basidiospores broadly ellipsoid, hyaline, smooth, slightly thick-walled, IKI-, CB-, 4--5(−5.2) × (−2.8)3--3.7(−3.9) μm, L = 4.5 μm, W =3.23 μm, Q = 1.4 (*n* = 60/1).

### Type of rot.

White rot.

![Basidiocarps of *Crassisporus microsporus*. Scale bars: 1 cm.](mycokeys-57-061-g009){#F9}

![Microscopic structures of *Crassisporus microsporus* (drawn from the holotype) **A** basidiospores **B** basidia and basidioles **C** cystidioles **D** hyphae from trama **E** hyphae from context.](mycokeys-57-061-g010){#F10}

Discussion {#SECID0EY1BI}
==========

In the present study, *Crassisporus* is proposed based on morphological characters and phylogenetic analyses. In the ITS+nLSU analysis, *Crassisporus* was nested in the core polyporoid clade with strong support (100% MP, 100% ML, 1.00 BPP; Fig. [1](#F1){ref-type="fig"}). A further study based on combined ITS+nLSU+mtSSU+EF1-α+RPB2 sequences data indicated that *Crassisporus* grouped with *Haploporus* with low support, but formed a monophyletic lineage with a strong support (100% MP, 100% ML, 1.00 BPP; Fig. [2](#F2){ref-type="fig"}). Morphologically, *Crassisporus* is characterized by the combination of an annual growth habit, effused-reflexed to pileate basidiocarps, pale yellowish brown to yellowish brown, concentrically zonate or sulcate pilei, velutinate pileal surface, a trimitic hyphal system with clamped generative hyphae, tissues turning to dark in KOH, oblong to broadly ellipsoid, hyaline, smooth and slightly thick-walled basidiospores.

Morphologically, the four *Crassisporus* species can be easily distinguished from each other. *Crassisporus microsporus* differs from other species by its small pores (5--7 per mm), and small broadly ellipsoid basidiospores (4--5 × 3--3.7 μm). Except for *C. imbricatus*, *C. leucoporus*, *C. macroporus*, and *C. microsporus*, all have fusoid cystidioles in the hymenium; moreover, *C. imbricatus* produces imbricate basidiocarps. Previously, the type specimen of *C. imbricatus* was identified as *Coriolopsis byrsina* (Mont.) Ryvarden based on morphological characters ([@B13]). After careful examination of the basidiospores along with DNA sequences analyses, the specimen was found to represent an unknown taxon. Here, we describe it as a new species of *Crassisporus* based on morphological characters and phylogenetic analysis. *Crassisporus macroporus* may be confused with *C. leucoporus* due to their similarity in effused-reflexed to pileate basidiocarps and oblong ellipsoid basidiospores, but *C. leucoporus* is distinguished from *C. macroporus* by its smaller pores (3--4 per mm), white pore surface when fresh, and acyanophilous skeletal and binding hyphae.

Phylogenetically, *Haploporus* groups together with *Crassisporus* (Figs [1](#F1){ref-type="fig"}, [2](#F2){ref-type="fig"}), but the former differs by its annual to perennial growth habit, dimitic to trimitic hyphal system, and ornamented, cyanophilous basidiospores ([@B28]; [@B3]).

*Crassisporus* is similar to *Hexagonia* Fr. and *Neofomitella* Y.C. Dai, Hai J. Li & Vlasák, because these genera share pileate brown basidiocarps, a trimitic hyphal system with clamped generative hyphae, and tissues becoming dark in KOH. However, *Hexagonia* is distinguished from *Crassisporus* by its larger hexagonal pores and thin-walled basidiospores ([@B20]). *Neofomitella* differs from *Crassisporus* in having crusted basidiocarps with the cuticle developing from base to margin, and smaller, thin-walled basidiospores ([@B16]).

Both *Perenniporia* Murrill and *Crassisporus* have hyaline and thick-walled basidiospores, but species of *Perenniporia* have cyanophilous, and variable dextrinoid skeletal hyphae. In addition, *Perenniporia* usually has truncate basidiospores ([@B7]; [@B20]; [@B36]; [@B3]).

*Truncospora* Pilát is similar to *Crassisporus* in having pileate basidiocarps and variable presence of cystidioles. However, *Truncospora* is distinguished from *Crassisporus* by variable dextrinoid and cyanophilous skeletal hyphae and truncate, strongly dextrinoid basidiospores ([@B35]; [@B3]).

*Abundisporus* Ryvarden and *Crassisporus* share effused-reflexed or pileate basidiocarps, but *Abundisporus* differs by its pale-umber to deep-purplish-brown or greyish- to umber-brown context, dimitic hyphal system, and pale-yellowish basidiospores ([@B27]; [@B37]; [@B3]).

*Perenniporiella* Decock & Ryvarden also has annual, pileate basidiocarps, and hyaline, thick-walled basidiospores, but it differs from *Crassisporus* in having a dimitic hyphal system ([@B4]).

*Grammothelopsis* Jülich is similar to *Crassisporus* in having thick-walled basidiospores; however, it differs from *Crassisporus* in its resupinate to effused basidiocarps with shallow irregular pores, and variable dextrinoid skeletal hyphae ([@B25]; [@B34]).

Key to species of *Crassisporus* {#SECID0ECLCI}
--------------------------------

  ---- ------------------------------------------------------------------------- ----------------------
  1    Cystidioles absent                                                        ***C. imbricatus***
  --   Cystidioles present                                                       **2**
  2    Basidiospores broadly ellipsoid                                           ***C. microsporus***
  --   Basidiospores oblong ellipsoid                                            **3**
  3    Pore surface cream, buff to cinnamon-buff when fresh, pores 2--3 per mm   ***C. macroporus***
  --   Pore surface white when fresh, pores 3--4 per mm                          ***C. leucoporus***
  ---- ------------------------------------------------------------------------- ----------------------

Supplementary Material
======================

###### XML Treatment for Crassisporus

###### XML Treatment for Crassisporus imbricatus

###### XML Treatment for Crassisporus leucoporus

###### XML Treatment for Crassisporus macroporus

###### XML Treatment for Crassisporus microsporus

We express our gratitude to Drs Tom May (Royal Botanic Gardens Victoria, Australia) and Yu-Cheng Dai (Beijing Forestry University) for arrangement of and assistance during field collections. The research was financed by the National Natural Science Foundation of China (Project Nos. 31670016, 31870008) and Beijing Forestry University Outstanding Young Talent Cultivation Project (No. 2019JQ03016).

[^1]: Academic editor: María P. Martín
