Introduction

We are carrying out a survey of freshwater fungi on submerged wood along a north-south gradient in the Asian region (Hyde et al. 2016a, 2016b). In this study, several Sporidesmium-like species were collected in Thailand and China and are identified based on morphology and phylogenetic analyses. Sporidesmium-like taxa are common on submerged wood in freshwater streams (Cai et al. 2002), and they have been reported to be polyphyletic across the Ascomycota (Shenoy et al. 2006). Hence, phylogenetic analyses and DNA sequence data are essential to determine their appropriate taxonomic placement (Shenoy et al. 2010, Su et al. 2016).

The asexual genus Sporidesmium was established by Link (1809) with S. atrum Link as the type. The generic characters include integrated, terminal, monoblastic, determinate or proliferating conidiogenous cells, distinctive, unbranched conidiophores, and acrogenous, solitary, transversely euseptate or distoseptate conidia (Ellis 1958, 1971). Sporidesmium is a large and heterogeneous genus. Presently, 477 epithets are referred to the genus in Index Fungorum (2017). However, many previously described species were revised and transferred to over 30 genera (Iturriaga et al. 2008). Thus, re-examination, combination, segregations or transfers have been frequently made for species of Sporidesmium sensu lato.

A reassessment of Sporidesmium sensu lato was initiated by Kirk (1982) who introduced the new genus Sporidesmiella with cuneate to obovoid conidia, with few septa. On the basis of the morphology of the conidiophores, type of the conidiogenous cells and the nature of conidial septation, Subramanian (1992) proposed five new genera (Ellisembia, Penzigomyces, Polydesmus, Repetophragma and Stanjehughesia) to accommodate some representative taxa in Sporidesmium, which were briefly discussed in Wu and Zhuang (2005). Hernández-Gutiérrez and Sutton (1997) segregated Imimyces and Linkosia from Sporidesmium based on the shape of conidiogenous cells and the absence/presence of conidiophores. Following Subramanian’s segregation, Shoemaker and Hambleton (2001) introduced the allied genus Imicles. However, the reliability of the above diagnostic characters was questioned by Réblová (1999) based on their variability in vitro and in vivo, and a lack of sexual morph connections (Seifert et al. 2011). Later, Penzigomyces and Imicles were merged into Sporidesmium and Ellisembia, respectively (Wu and Zhuang 2005). Recently, Su et al. (2016) synonymized Ellisembia under Sporidesmium.

Phylogeny-based studies have been carried out to further re-examine the classification of Sporidesmium-like taxa, given that the generic delimitations based on morphological characters appear to be questionable. Shenoy et al. (2006) found that Sporidesmium and morphologically similar genera are clearly not monophyletic, as they are distributed among different families and orders within Dothideomycetes and Sordariomycetes. Su et al. (2016) reported similar results. A monophyletic clade with species resembling the type species of Sporidesmium was designated as Sporidesmiaceae sensu stricto, and a new Sporidesmium-like genus was introduced as Distoseptispora (Su et al. 2016).

To clarify the taxonomy of several Sporidesmium-like strains collected in this study, we analysed a combined LSU, SSU, TEF1α, RPB2 and ITS sequence dataset and examined morphological characters. The new clades are introduced as new genera and species with illustrated accounts and molecular support. Our decisions regarding new taxa follow the recommendations of Jeewon and Hyde (2016). An emended description of Distoseptispora is provided, and the systematic positions of the Sporidesmium-like taxa are discussed.

Materials and methods

Collection and examination of specimens

Specimens of submerged, decaying wood were collected from streams in Prachuap Khiri Khan and Phang Nga Provinces, Thailand, in December 2014, 2015 and Guizhou Province, China, in October 2016. Specimens were brought to the laboratory in plastic bags and incubated in plastic boxes lined with moistened tissue paper at room temperature for one week. Morphological observations were made using a Motic SMZ 168 Series dissecting microscope for fungal structures on natural substrate. The fungal structures were collected using a syringe needle and transferred to a small drop of distilled water on a clean slide and covered with a cover glass. The fungi were examined using a Nikon ECLIPSE 80i compound microscope and photographed with a Canon 600D digital camera fitted to the microscope. Measurements were made with the Tarosoft (R) Image Frame Work program and images used for figures were processed with Adobe Photoshop CS6 software. Single spore isolations were made onto potato dextrose agar (PDA) or water agar (WA) and later transferred onto malt extract agar (MEA) or PDA following the method of Chomnunti et al. (2014). Specimens (dry wood with fungal material) are deposited in the herbarium of Mae Fah Luang University (MFLU), Chiang Rai, Thailand and Guizhou Academic of Agriculture Sciences (GZAAS), China. Axenic cultures are deposited in Mae Fah Luang University Culture Collection (MFLUCC) and Guizhou Culture Collection (GZCC). Facesoffungi and MycoBank numbers are registered as outlined in Jayasiri et al. (2015) and MycoBank (2017).

DNA extraction, PCR amplification and sequencing

Isolates were grown on PDA/MEA medium at 25 °C for one month. Fungal mycelium was scraped off and transferred to a 1.5-mL microcentrifuge tube using a sterilized lancet for genomic DNA extraction. A Biospin Fungus Genomic DNA Extraction Kit (BioFluxR, Hangzhou, P. R. China) was used to extract DNA following the manufacturer’s instructions. LSU, SSU, TEF1α, RPB2 and ITS gene regions were amplified using the primer pairs LROR/LR5, NS1/NS4, EF1-983F/EF1-2218R, RPB2-5F/RPB2-7cR and ITS5/ITS4 (Vilgalys and Hester 1990, Liu et al. 1999). The amplifications were performed in a 25 μL reaction volume containing 9.5 μL ddH2O, 12.5 μL 2 × PCR Master Mix (TIANGEN Co., China), 1 μL of DNA template and 1 μL of each primer (10 μM). The amplification conditions for ITS, LSU, SSU and TEF1α consisted of initial denaturation at 94 °C for 3 min; followed by 40 cycles of 45 s at 94 °C, 50 s at 56 °C and 1 min at 72 °C, and a final extension period of 10 min at 72 °C. The amplification conditions for RPB2 gene consisted of initial denaturation at 95 °C for 5 min; followed by 37 cycles of 15 s at 95 °C, 50 s at 56 °C and 2 min at 72 °C, and a final extension period of 10 min at 72 °C. Purification and sequencing of PCR products were carried out using the above-mentioned PCR primers at Invitrogen Biotechnology Co., China.

Phylogenetic analyses

The taxa included in the phylogenetic analyses were selected and obtained from previous studies and GenBank (Shenoy et al. 2006, Maharachchikumbura et al. 2015, 2016, Su et al. 2016). Five gene regions (LSU, SSU, TEF1α, RPB2 and ITS) were used for the combined sequences analyses. Sequences were optimized manually to allow maximum alignment and maximum sequence similarity. The sequences were aligned using the online multiple alignment program MAFFT v.7 (http://mafft.cbrc.jp/alignment/server/) (Katoh and Standley 2013). The alignments were checked visually and improved manually where necessary.

Phylogenetic analysis of the sequence data consisted of maximum likelihood (ML) using RAxML-HPC v.8 (Stamatakis 2006, Stamatakis et al. 2008) on the XSEDE Teragrid of the CIPRES science Gateway (https://www.phylo.org) (Miller et al. 2010) with rapid bootstrap analysis, followed by 1000 bootstrap replicates. The final tree was selected among suboptimal trees from each run by comparing likelihood scores under the GTRGAMMA substitution model.

The program MrModeltest2 v. 2.3 (Nylander 2008) was used to infer the appropriate substitution model that would best fit the model of DNA evolution for the combined datasets for Bayesian inference analysis with the GTR+G+I substitution model selected. Posterior probabilities (PP) (Rannala and Yang 1996, Zhaxybayeva and Gogarten 2002) were determined by Markov Chain Monte Carlo sampling (BMCMC) in MrBayes v. 3.0b4 (Huelsenbeck and Ronquist 2001). Six simultaneous Markov chains were run for 5 million generations, with trees sampled every 100 generations. The first 10,000 trees, representing the burn-in phase of the analyses, were discarded and the remaining trees were used for calculating posterior probabilities (PP) in the majority rule consensus tree (Larget and Simon 1999).

The resulting trees were printed with FigTree v. 1.4.0 (http://tree.bio.ed.ac.uk/software/figtree/), and the layout was created in Microsoft PowerPoint for Mac v. 15.19.1. The alignment of phylogenetic analyses was deposited in TreeBASE (20968). Sequences generated in this study are deposited in GenBank (Table 1).

Table 1 Isolates used in the phylogenetic analyses and their corresponding GenBank numbers
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Phylogenetic results

The analysed dataset consisted of combined LSU (930 bp), SSU (1037 bp), TEF1α (933 bp), RPB2 (1086 bp) and ITS (655 bp) sequence data (a total of 4641 characters including gaps) for 125 taxa in Sordariomycetes with Botryotinia fuckeliana and Dothidea sambuci as the outgroup taxa. The best scoring RAxML tree is shown in Fig. 1.

Fig. 1
figure 1figure 1

Maximum likelihood majority rule consensus tree based on a dataset of combined LSU, SSU, TEF1α, RPB2 and ITS sequence data. High branch support is shown at the nodes, maximum likelihood bootstrap support (ML BS) ≥ 70 % and Bayesian posterior probability (PP) ≥ 0.90. The scale bar represents the expected number of changes per site. The tree is rooted with Botryotinia fuckeliana and Dothidea sambuci. The strain numbers are noted after the species names. The new species are in blue bold, Sporidesmium-like taxa are in orange background. Branches with 100 % ML BS and 1.0 PP are showed in black dots. Subclasses are indicated as coloured blocks, orders and families are indicated with right brackets

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Phylogenetic analyses indicate that Ellisembia, Linkosia, Sporidesmium and Stanjehughesia are polyphyletic. A new genus Pseudostanjehughesia is established to accommodate the distinct taxon P. aquitropica (MFLUCC 16-0569) which is a sister taxon to Papulosaceae with good support. A sexual taxon, Sporidesmium thailandense (MFLUCC 15-0617), clustered together with the ex-type Sporidesmium thailandense (MFLUCC 15-0964) and nested in Sporidesmiaceae sensu stricto. They are shown to be the same species based on both morphological and molecular data. Distinct from Sporidesmiaceae sensu stricto, two isolates of Sporidesmium tropicale (MFLUCC 16-0185 and HKUCC 10838) clustered with Bullimyces communis (AF 281-3) as sister taxa, and the new species Sporidesmium gyrinomorphum (MFLUCC 16-0186) was nested in Xylariomycetidae among several Sporidesmium-like taxa. The other five newly obtained strains were placed in Distoseptisporaceae. Two Distoseptispora suoluoensis strains (MFLUCC 17-0224 and MFLUCC 17-1305) formed the basal position in Distoseptisporaceae with strong support. The distinction of Distoseptispora guttulata (MFLUCC 16-0183) is also well-supported. Distoseptispora phangngaensis (MFLUCC 16-0857) is placed as sister taxon to D. aquatica but weakly supported. The strain MFLUCC 16-1044 grouped with D. multiseptata; they are the same species.

Taxonomy

Distoseptispora K.D. Hyde, McKenzie & Maharachch., Fungal Divers. 80(1): 402 (2016).

MycoBank number: MB551833, Facesoffungi number: FoF01755

Emended description: Colonies on the substratum superficial, effuse, hairy or velvety, olivaceous or black. Mycelium mostly immersed, composed of branched, septate, smooth, pale brown hyphae. Sexual morph: Undetermined. Asexual morph: Conidiophores macronematous, mononematous, septate, unbranched, single or in groups, erect, straight or flexuous, smooth, olivaceous to brown, cylindrical, robust at the base. Conidiogenous cells monoblastic, integrated, determinate, terminal, cylindrical, sometimes with percurrent proliferation. Conidia acrogenous, solitary, olivaceous, brown or yellowish/reddish brown, euseptate or distoseptate, obclavate or cylindrical with rounded apex, length indeterminate or with percurrent proliferation, truncate at the base, basal cell with cross wall and basal scar. Conidial secession schizolytic.

Type species: Distoseptispora fluminicola McKenzie, H.Y. Su, Z.L. Luo & K.D. Hyde

Distoseptispora guttulata J. Yang & K.D. Hyde, sp. nov. Fig. 2

MycoBank number: MB821271, Facesoffungi number: FoF03357

Etymology: Referring to the guttulate conidia.

Holotype: MFLU 17-0852

Fig. 2
figure 2

Distoseptispora guttulata (MFLU 17-0852) a Conidiophores with conidia on substrate. b Conidiophore. c–e Conidiophores with conidia. f Conidiogenous cell. h–k Conidia. g Germinated conidium on PDA medium. l, m Culture, l from above. Scale bars: a, c = 50 μm, b, d, e, g–k = 30 μm, f = 20 μm

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Saprobic on decaying plant substrates. Colonies effuse, olivaceous or black, hairy or velvety. Mycelium partly superficial, partly immersed, consisting of branched, septate, smooth, subhyaline to pale brown hyphae. Conidiophores macronematous, mononematous, mid or dark brown, 3–4(–10)-septate, solitary or caespitose, smooth, straight or slightly flexuous, cylindrical, 55–90(–145) × 3.5–5.5 μm (\( \overline{x} \) = 75 × 4.5 μm, n = 15), rounded at the apex. Conidiogenous cells monoblastic, integrated, terminal, determinate, mid to dark brown, cylindrical, sometimes proliferating percurrently. Conidia acrogenous, solitary, holoblastic, obclavate or lanceolate, rostrate, straight or slightly curved, 11–14(–20)-euseptate, mid to dark brown, or olivaceous, smooth, 75–130(–165) × 7–11 μm (\( \overline{x} \) = 105 × 9 μm, n = 25), truncate at the base, tapering to the apex.

Cultural characteristics: Conidia germinating on PDA within 24 h and germ tubes produced from both ends. Colonies on MEA reaching 5–10 mm diam. at 7 days at 25 °C, in natural light, with fluffy, dense, dark olivaceous mycelium in the center, becoming sparse and paler at the entire margin; in reverse with dark brown, pale brown at the smooth margin.

Material examined: THAILAND, Prachuap Khiri Khan Province, near 12°30.195′N, 99°31.350′E, on decaying wood submerged in a freshwater stream, 25 December 2014, Jaap van Strien, Site 5-16-3 (MFLU 17-0852 holotype, GZAAS 17-0005 isotype), ex-type living culture, MFLUCC 16-0183, GZCC 15-0076.

Notes: Distoseptispora guttulata clusters in Distoseptispora based on multi-gene analyses. Distospetispora guttulata is easily distinguished from other species in Distoseptisporaceae by its euseptate conidia and its cylindrical, percurrent conidiogenous cells which have a rounded apex. Distospetispora guttulata resembles D. leonensis (= Ellisembia leonensis (M.B. Ellis) McKenzie) in having conspicuous long conidiophores (70–130 μm long), which are twice to three times longer than in the other species (30–40 μm long) of the genus. Distoseptispora leonensis differs from the new species by having shorter and wider, obclavate, fusiform to ellipsoidal conidia. The cuspate conidial apex of the new taxon is also different from the broader and rounded apex of D. adscendens (= Ellisembia adscendens (Berk.) Subram.), D. aquatica, D. fluminicola McKenzie, H.Y. Su, Z.L. Luo & K.D. Hyde, D. multiseptata, D. tectonae Doilom & K.D. Hyde and D. tectonigena Doilom & K.D. Hyde. Distoseptispora guttulata is similar to Ellisembia longispora W.P. Wu, which lacks molecular data. They share the same conidial shape and similar size of conidia and conidiophores, both having darkened scars at the base of the conidia. However, E. longispora is distinguishable from the new species by its distoseptate conidia and lageniform or doliiform conidiogenous cells.

Distoseptispora multiseptata J. Yang & K.D. Hyde, Fungal Divers 80: 220 (2016) Fig. 3

MycoBank number: MB552206, Facesoffungi number: FoF02244

Fig. 3
figure 3

Distoseptispora multiseptata (MFLU 17-0856) a Colonies on natural substrate. b Conidium with conidiophore. c–e, g, h Conidia. f Conidiophores. i Germinating conidium. j, k Culture, j from above, k from below. Scale bars: a = 200 μm, b, d, e, g–i = 100 μm, c = 50 μm, f = 30 μm

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Material examined: THAILAND, Prachuap Khiri Khan Province, near 12°30.195′N, 99°31.350′E, on decaying wood submerged in a freshwater stream, 25 December 2014, Jaap van Strien, Site 5-23-2 (MFLU 17-0856, GZAAS 17-0009), living culture, MFLUCC 16-1044, GZCC 16-0012.

Notes: Molecular analyses showed the strain MFLUCC 16-1044 clusters with the ex-type of Distoseptispora multiseptata. The morphological examination of this collection revealed conidiophores 25–50 μm long but with conidia up to 700 μm long. Interestingly, the conidial length of this collection (mostly 300–600 μm long, up to 700 μm long) are significantly longer than those of the holotype (up to 380 μm long), and also much longer than in the other species of Distoseptispora, even in Ellisembia, and Sporidesmium. The length of the conidia may depend on the length of incubation, but this has not been established. The elongated, obclavate or cylindrical, distoseptate conidia and short conidiophores of our isolate resemble those of other species in the genus.

Distoseptispora phangngaensis J. Yang, Maharachch. & K.D. Hyde, sp. nov. Fig. 4

MycoBank number: MB821272, Facesoffungi number: FoF03358

Etymology: Referring to the collecting site from Phang Nga Province in Thailand.

Holotype: MFLU 17-0855

Fig. 4
figure 4

Distoseptispora phangngaensis (MFLU 17-0855) a Colony on submerged wood. b−g Conidia and conidiophores. h Germinated conidium on PDA. i, j Culture, i from above, j from below. Scale bars: a = 200 μm, b−h = 50 μm

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Saprobic on decaying plant substrates. Colonies effuse, dark olivaceous, hairy. Mycelium partly superficial, partly immersed in the substrate, comprised of branched, septate, hyaline to pale brown hyphae. Conidiophores macronematous, mononematous, solitary, brown, 2−3-septate, straight, or slightly flexuous, tapering distally, truncate at the apex, 18–30(–40) × 4.3–6.5 μm (\( \overline{x} \) = 27 × 5.5 μm, n = 10). Conidiogenous cells monoblastic, integrated, terminal, brown, determinate. Conidia acrogenous, solitary, elongate, obclavate, rostrate, multi-distoseptate, tapering towards the rounded apex, dark olivaceous to mid or dark brown, 165–350 × 14–19 μm (\( \overline{x} \) = 260 × 16 μm, n = 25), with basal cell subcylindrical.

Cultural characteristics: Conidia germinating on PDA within 24 h and germ tubes produced from several cells. Colonies on PDA reaching 5–10 mm diam. at 7 days at 25 °C, in natural light, circular, with fluffy, dark brown mycelium on the surface with entire margin, in reverse dark brown to black.

Material examined: THAILAND, Phang Nga Province, Bann Tom Thong Khang, on decaying wood submerged in a freshwater stream, 17 December 2015, Kevin D. Hyde, Site 7-2-4 (MFLU 17-0855 holotype, GZAAS 17-0008 isotype), ex-type living culture, MFLUCC 16-0857, GZCC 17-0013.

Notes: Distoseptispora phangngaensis shares the same morphological characters as D. adscendens in the shape and size of conidia and conidiophores. However, they are phylogenetically distinct. Distoseptispora phangngaensis is the sister taxon to D. aquatica with weak support. It has longer conidia than those of D. aquatica. Conidia are mid to dark brown in D. phangngaensis, but bluish green to malachite green in D. aquatica.

Distoseptispora suoluoensis J. Yang, Maharachch. & K.D. Hyde, sp. nov. Fig. 5

MycoBank number: MB821273, Facesoffungi number: FoF03359

Etymology: Referring to the collecting site from the Suoluo river in China.

Holotype: MFLU 17-0853

Fig. 5
figure 5

Distoseptispora suoluoensis (MFLU 17-0853) a Colonies on natural substrate. b Conidium with conidiophore. c Conidiophore. d Conidiogenous cell bearing conidium. e–g, k Conidia. h–j Conidia with proliferation. l Germinating conidium. m, n Culture, m from above, n from below. Scale bars: a–c = 50 μm, d, f–l = 30 μm, e = 20 μm

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Saprobic on decaying plant substrates. Colonies effuse, brown, hairy, glistening, often inconspicuous. Mycelium partly superficial, partly immersed in the substratum, composed of hyaline to pale brown, septate, branched hyphae. Conidiophores macronematous, mononematous, solitary or aggregated at the base, cylindrical, straight or slightly flexuous, septate, dark brown, paler at the apical part, 80–250 × 4.5–5.8 μm (\( \overline{x} \) = 165 × 5.2 μm, n = 30), rounded at the apex. Conidiogenous cells integrated, terminal, monoblastic, cylindrical, brown. Conidia acrogenous, solitary, narrowly obclavate or obspathulate, rostrate, 8–10-euseptate, rarely 12–14-septate, yellowish brown or dark olivaceous, becoming paler or hyaline towards the apex, guttulate, verrucose, (65–)80–125(–145) × 8–13 μm (\( \overline{x} \) = 100 × 10 μm, n = 30), 2.5–4.5 μm wide at the base and 2–3.5 μm wide at the apex, with a darkened scar at the base, sometimes with percurrent proliferation which forms another conidium from the conidial apex.

Cultural characteristics: Conidia germinating on WA within 24 h and germ tubes produced from both ends. Colonies on PDA reaching 5–10 mm diam. at two weeks at 25 °C, in natural light, circular, with dense, dark olivaceous mycelium on the surface with entire margin; in reverse dark green to black.

Material examined: China, Guizhou Province, Anshun city, Gaodang village, 26°4.267′N, 105°41.883′E, on decaying wood submerged in the Suoluo river, 19 October 2016, Jing Yang, GD 3-2 (MFLU 17-0853 holotype, GZAAS 17-0006 isotype), ex-type living culture MFLUCC 17-0224, GZCC 17-0038; GD 4-3 (MFLU 17-0854, GZAAS 17-0007 paratype), living culture MFLUCC 17-1305.

Notes: Distoseptispora suoluoensis is distinct with strong molecular support from other species in the genus. Distoseptispora suoluoensis shares morphological characters with D. guttulata in having long conidiophores with rounded apex and euseptate conidia, but with different conidial colour and shape. Greater similarity was found between D. suoluoensis and Sporidesmium tropicale in size and shape of their conidiophores and conidia. The conidiogenous cells of D. suoluoensis are lageniform or cylindrical with truncate apex, while cylindrical with rounded apex in S. tropicale. Additionally, the percurrent proliferation of conidia was not observed in S. tropicale.

Pseudostanjehughesia J. Yang & K.D. Hyde, gen. nov.

MycoBank number: MB821274, Facesoffungi number: FoF03360

Etymology: Referring to the morphologically similar genus Stanjehughesia.

Saprobic on decaying plant substrates. Asexual morph: Colonies effuse, dark brown, scattered, glistening. Mycelium partly superficial, partly immersed in the substratum, composed of brown, septate, branched hyphae. Conidiophores macronematous, mononematous, solitary, cylindrical, slightly tapering towards the apex, straight or flexuous, septate, mid to dark brown, sometimes reduced to a single conidiogenous cell, truncate at the apex. Conidiogenous cells integrated, terminal, monoblastic, cylindrical, brown. Conidia acrogenous, solitary, fusiform or obclavate, septate, mid to dark brown, becoming paler towards the apex, truncate at the base. Sexual morph: Undetermined.

Type species: Pseudostanjehughesia aquitropica J. Yang & K.D. Hyde

Pseudostanjehughesia aquitropica J. Yang & K.D. Hyde, sp. nov. Fig. 6

MycoBank number: MB821275, Facesoffungi number: FoF03361

Etymology: Referring to the freshwater habitat and collecting site in a tropical country, Thailand.

Holotype: MFLU 17-0857

Fig. 6
figure 6

Pseudostanjehughesia aquitropica (MFLU 17-0857) a Colony on substrate. b–e, j Conidiophores with conidia. f–i Conidia. k Conidiophore. l Germinated conidium on PDA medium. m, n Culture, n from above. Scale bars: a = 50 μm, b, f, k = 10 μm, c–e, g–j, l = 20 μm

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Saprobic on decaying plant substrates. Colonies effuse, dark brown, scattered, glistening. Mycelium partly superficial, partly immersed in the substratum, composed of brown, septate, branched hyphae. Conidiophores macronematous, mononematous, solitary, cylindrical, slightly tapering towards the apex, straight or flexuous, 0–2-septate, dark brown, 9–20 × 4–7 μm (\( \overline{x} \) = 14 × 5.5 μm, n = 15), truncate at the apex, sometimes reduced to a single conidiogenous cell. Conidiogenous cells integrated, terminal, monoblastic, cylindrical, brown. Conidia acrogenous, solitary, oval or ellipsoidal when young, fusiform or obclavate when mature, rostrate, 5–16-euseptate, verrucose, mid to dark brown, tapering and becoming pale brown towards the apex, guttulate, 55–120 × 15–25 μm (\( \overline{x} \) = 80 × 20 μm, n = 40), truncate at the base.

Cultural characteristics: Conidia germinating on PDA within 24 h and germ tubes produced from both ends. Colonies on PDA slow-growing, reaching 10–15 mm diam. at one month at 25 °C, in natural light, circular, layered, with sparse, dark brown mycelium on the surface with undulate margin; in reverse dark brown to black.

Material examined: THAILAND, Prachuap Khiri Khan Province, near 12°30.195′N, 99°31.350′E, on decaying wood submerged in a freshwater stream, 25 December 2014, Jaap van Strien, Site 5-25-1 (MFLU 17-0857 holotype, GZAAS 17-0010 isotype), ex-type living culture MFLUCC 16-0569, GZCC 15-0079.

Notes: Pseudostanjehughesia aquitropica resembles species of Stanjehughesia and Linkosia because of the absence or reduced conidiophores, and brown and obclavate conidia. Species of Linkosia are easily distinguished from Pseudostanjehughesia by the lageniform or ampulliform conidiogenous cells and distoseptate conidia. It is more difficult to separate Pseudostanjehughesia from Stanjehughesia because both genera share similar morphological characters of conidiophores, conidiogenous cells and conidia. However, they are phylogenetically distinct. Stanjehughesia polypora is placed within Xylariomycetidae, while St. vermiculata (Cooke) Subram., Umbrinosphaeria caesariata (Clinton & Peck) Réblová (sexual morph of St. hormiscioides (Corda) Subram.) and Linkosia sp. clustered within Sordariomycetidae, but Ps. aquitropica is the sister taxon to the Papulosaceae within Diaporthomycetidae. In Papulosaceae, Pleurophragmium is the only asexual genus, and there are no asexual morphs observed from the sexual genera (Réblová 2009). Morphologically, Pleurophragmium is distinct from Pseudostanjehughesia in having well-defined macronematous conidiophores, sympodial, intercalary, polyblastic, denticulate conidiogenous cells with pointed denticles and solitary apical and lateral conidia with pointed bases (Ellis 1971, 1976). Pseudostanjehughesia aquitropica is similar to St. decorosa (R.F. Castañeda & W.B. Kendr.) McKenzie by the macronematous or reduced conidiophores, cylindrical conidiogenous cells and verrucose, obclavate conidia. Stanjehughesia decorosa, however, has larger conidiophores or conidiogenous cells (20–30 × 10–15 μm) with longer and narrower conidia (170–200 × 12–17 μm). Stanjehughesia minima W.P. Wu and St. floridensis G. Delgado are also morphologically close to the new taxon, but differ in having lageniform or ampulliform conidiogenous cells and smaller conidia, which are 34–48 × 8.5–10 μm for St. minima and 32–48 × 6–7 μm for St. floridensis.

Sporidesmium gyrinomorphum J. Yang, Maharachch. & K.D. Hyde, sp.nov. Fig. 7

MycoBank number: MB821276, Facesoffungi number: FoF03362

Etymology: Referring to the tadpole-shaped conidia.

Holotype: MFLU 17-0851

Fig. 7
figure 7

Sporidesmium gyrinomorphum (MFLU 17-0851) a Conidiophore with conidium on substrate. b Conidiophore with conidium. c Conidiophore. d Conidiogenous cell. e Conidiogenous cell with conidium. f–h Conidia. i Germinated conidium on PDA medium. j, k Culture, j from above. Scale bars: a–c = 100 μm, d = 50 μm, e–i = 30 μm

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Saprobic on decaying plant substrates. Asexual morph: Colonies effuse, dark brown to black, hairy, glistening. Mycelium partly superficial, partly immersed in the substratum, composed of brown, septate, branched hyphae. Conidiophores macronematous, mononematous, solitary, cylindrical, straight or slightly flexuous, septate, dark brown, slightly tapering towards the apex, 360–650(–740) × 7–18 μm (\( \overline{x} \) = 525 × 11 μm, n = 15), rounded at the apex. Conidiogenous cells integrated, terminal, monoblastic, cylindrical, brown, sometimes with percurrently proliferations through the scar, with successive conidia seceding at progressively higher levels. Conidia acrogenous, solitary, obclavate to obspathulate, tapering to the apex, rostrate, 7–8-euseptate, mid to dark brown, becoming pale brown towards the apex, guttulate, 80–160 × 16.5–22 μm (\( \overline{x} \) = 105 × 20 μm, n = 15), truncate at the base. Sexual morph: Undetermined.

Cultural characteristics: Conidia germinating on PDA within 24 h and germ tubes produced from both ends. Colonies on MEA reaching 5–10 mm diam. at 14 days at 25 °C, in natural light, circular, with fluffy, dense, dark olivaceous mycelium on the rings-like surface with entire margin; in reverse dark green to black.

Material examined: THAILAND, Prachuap Khiri Khan Province, near 12°30.195′N, 99°31.350′E, on decaying wood submerged in a freshwater stream, 25 December 2014, Jaap van Strien, Site 5-26-1 (MFLU 17-0851 holotype, GZAAS 17-0004 isotype), ex-type living culture MFLUCC 16-0186, GZCC 15-0080.

Notes: The phylogenetic analyses indicated that Sporidesmium gyrinomorphum is close to Ellisembia calyptrata (Cabello, Cazau & Aramb.) W.P. Wu, Sporidesmium macrurum (Sacc.) M.B. Ellis, Sporidesmina malabarica Subram. & Bhat and Stanjehughesia polypora W.P. Wu within Xylariomycetidae, which is distant from the Sporidesmiaceae sensu stricto. In this case, we prefer to introduce it within Sporidesmium sensu lato based on its distinctive conidiophores, cylindrical conidiogenous cells with percurrent proliferation and obclavate, rostrate conidia. Sporidesmium gyrinomorphum is morphologically similar to Penzigomyces flagellatus (S. Hughes) Subram. in conidial ontogeny and conidial shape. The conidiogenous cells of both species often proliferate through the scar after the first conidium has fallen and form another conidium at a higher level (Ellis 1958). However, the conidiophores of S. gyrinomorphum (350–750 μm long, 7–18 μm wide) are much longer than those of Pe. flagellatum (50–280 μm long, 5–7 μm wide). The conidia of S. gyrinomorphum (80–160 μm long, 15–25 μm wide) are also longer than in Pe. flagellatum (55–105 μm long, 10–11 μm wide). Additionally, S. gyrinomorphum is characterized by a cylindrical conidiogenous cell while Pe. flagellatum has lageniform conidiogenous cells. The apex of conidiophores in S. gyrinomorphum is rounded, while truncate in Pe. flagellatum.

Sporidesmium thailandense W. Dong, H. Zhang & K.D. Hyde, Fungal Divers 85: 103 (2017) Fig. 8

MycoBank number: MB553768, Facesoffungi number: FoF03347

Fig. 8
figure 8

Sporidesmium thailandense (MFLU 15-1152) a Immersed ascomata on natural substate. b Asci coming out. c, d Sections of ascoma. e Section of peridium at the side. f Section of under peridium. g Paraphyses. h–k Asci. l–s Ascospores. t Germinated spore. u Apical ring. v, w Culture, v from above, w from below. Scale bars: a = 200 μm, b–d = 100 μm, e, f, p–s = 10 μm, g, l–o = 15 μm, h–k = 40 μm, t–u = 20 μm

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Material examined: THAILAND, Prachuap Khiri Khan Province, on submerged wood, 25 December 2014, Jaap van Strien, Site4 18-5 (MFLU 15-1152); living culture, MFLUCC 15-0617.

Notes: This collection is identified as Sporidesmium thailandense based on both morphological characters and molecular data. Zhang et al. (2017) observed the 3-septate conidia. In this collection, conidia are mostly 4-septate and some bearing appendages, ascomata turn to dark brown with age.

Sporidesmium tropicale M.B. Ellis, Mycol Pap 70: 58 (1958) Fig. 9

MycoBank number: MB 306326, Facesoffungi number: FoF03363

Fig. 9
figure 9

Sporidesmium tropicale (MFLU 17-0850) a Conidiophore with conidium on substrate. b Conidiophore. c, d Conidia. e Germinated conidium on PDA medium. f Conidiophore with conidium. g Conidiogenous cell. h, i Culture, h from above. Scale bars: a = 50 μm, b, f = 30 μm, c–e = 20 μm, g = 10 μm

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Material examined: THAILAND, Prachuap Khiri Khan Province, near 12°30.195′N, 99°31.350′E, on decaying wood submerged in a freshwater stream, 25 December 2014, Jaap van Strien, Site 5-23-1 (MFLU 17-0850), living culture, MFLUCC 16-0185, GZCC 15-0078.

Notes: Sporidesmium tropicale is characterized by non-proliferating conidiogenous cells, obclavate, rostrate and verrucose conidia. It was found on dead branches of many woody plants and is widely distributed in tropical areas including China, Ghana, Jamaica, Malaysia, Nigeria, Papua New Guinea, Sierra Leone, Sri Lanka, and USA (Ellis 1958, Wu and Zhuang 2005). The morphological characters of this collection are the same as in the holotype. Phylogenetic analyses showed this collection clusters with S. tropicale (HKUCC 10838).

Discussion

Approximately one fifth of described fungi are thought to be asexual and clonal or recombining (Taylor et al. 1999). Due to the absence of sexual reproduction, the classification of asexual fungi has led to an artificial system (Shenoy et al. 2006). Sporidesmium-like taxa are common in terrestrial habitats (Wu and Zhuang 2005) and have frequently been recorded from wood submerged in freshwater (Hyde and Goh 1998, Ho et al. 2001, Cai et al. 2003). In this study, we collected several new Sporidesmium-like taxa from streams in Thailand and China. Shenoy et al. (2006) mentioned that Sporidesmium and its related genera are an interesting group as they share characters in having holoblastic, septate conidia and monoblastic, determinate or percurrent conidiogenous cells, but are polyphyletic in nature and difficult to classify based on morphology alone. In this study, we follow Seifert et al. (2011) to accept all the segregated genera as morphologically distinctive groups and synonymize species and combinations with evidence from molecular data.

Phylogenetic analyses show that five hyphomycetous strains are placed in Distoseptisporaceae in a robust clade. Distoseptispora guttulata and D. suoluoensis differ from other species in the genus in having much longer, percurrently proliferating (observed in D. guttulata) conidiophores and euseptate conidia. Consequently, the emended generic concept of Distoseptispora was provided. Distoseptispora multiseptata was re-collected at Prachuap Khiri Khan Province in Thailand, where the holotype was collected. However, the fresh collection has much longer conidia (up to 700 μm long) than conidia in the holotype specimen (up to 380 μm long). Distoseptispora phangngaensis is morphologically similar to D. adscendens but phylogenetically distant.

An LSU sequence is the only available sequence of Sporidesmium tropicale (HKUCC 10838). Its systematic position appears questionable. Shenoy et al. (2006) performed a parsimony analysis based on LSU sequences, that indicated that S. tropicale (HKUCC 10838) was basal in Annulatascaceae, close to Sporidesmiaceae sensu stricto. In Su et al. (2016), an ML tree was constructed with LSU sequence data and showed S. tropicale (HKUCC 10838) to cluster in Sporidesmium sensu stricto as a basal taxon. In this study, Sporidesmium tropicale (HKUCC 10838) and S. tropicale (MFLUCC 16-0185) are distinct from Sporidesmium sensu stricto, but close to Papulosaceae, which is in the Diaporthomycetidae family incertae sedis. A combined multi-gene analyses may lead to a more natural classification. Sporidesmium gyrinomorphum was placed among several Sporidesmium-related genera within Xylariomycetidae. Although its morphological characters are accepted in both Sporidesmium and Distoseptispora, we prefer naming this fungus under Sporidesmium sensu lato, and accept the monophyletic genus Distoseptispora.

The Sporidesmium-like taxa have undergone convergent evolution and many of the morphological characters used to delimit the genera do not appear phylogenetically significant (Shenoy et al. 2006, Su et al. 2016). Molecular data is needed to distinguish and place these taxa. Thus, we propose a new genus Pseudostanjehughesia based on its phylogenetic segregation and morphology. There are few morphological differences between Pseudostanjehughesia and Stanjehughesia. Despite the septation type, Pseudostanjehughesia aquitropica is neither close to Stanjehughesia (in Sordariomycetidae and Xylariomycetidae) nor Linkosia (in Hypocreomycetidae, Sordariomycetidae and Diaporthomycetidae) according to multi-gene analyses. It is placed as a sister taxon to Papulosaceae and treated as incertae sedis in Diaporthomycetidae. As Sporidesmium-like morphologies were found in different classes, phylogenetic studies with more taxa and gene regions are necessary to be used to assign their placement.

Sporidesmium thailandense is the first known sexual morph in the genus linked with molecular data, without a known asexual morph (Zhang et al. 2017). In this study, we identified one collection as S. thailandense based on both morphological characters and molecular data. Shenoy et al. (2006), and Wu and Zhuang (2005) have listed the previous studies on connections of sexual-asexual morphs, which considered Akaropeltella, Cucurbitaria, Eupelte and Placosoma within Dothideomycetes, and Chaetosphaeria, Eriosphaeria, Lecythothecium, Miyoshiella and Umbrinosphaeria within Sordariomycetes to be associated with Sporidesmium-like asexual morphs. However, only a few sexual and asexual morph connections (Lecythothecium duriligni Réblová & Winka and Sporidesmium folliculatum (Corda) E.W. Mason & S. Hughes, Umbrinosphaeria caesariata and Stanjehughesia hormiscioides) were well-established by cultural and molecular studies (Réblová 1999, Réblová and Winka 2001). Thus, more collections with molecular data and epitypifications (Ariyawansa et al. 2014) are desired to investigate the connections between fungi of the Sporidesmium complex and their sexual morphs.