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Research Article
Morphological and multi-gene phylogenetic analyses reveal Nigrellomyces gen. nov. and one new species in Pleurotheciaceae from China
expand article infoWang-ming Zhang‡, Xiao-yu Song‡, Wan-qing Xie‡, Xin-zhong Zhou‡, Juan Lu‡, Qin-ying Feng‡
‡ Beijing Jishuitan Hospital Guizhou Hospital, Guiyang, China

Corresponding author: Qin-ying Feng ( 57105762@qq.com )

Academic editor: Huzefa Raja
© 2025 Wang-ming Zhang, Xiao-yu Song, Wan-qing Xie, Xin-zhong Zhou, Juan Lu, Qin-ying Feng.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation: Zhang W, Song X, Xie W, Zhou X, Lu J, Feng Q (2025) Morphological and multi-gene phylogenetic analyses reveal Nigrellomyces gen. nov. and one new species in Pleurotheciaceae from China. MycoKeys 122: 277-292. https://doi.org/10.3897/mycokeys.122.164540
Open Access

Abstract

Nigrellomyces is introduced herein as a new genus to accommodate a novel asexual ascomycete, Nigrellomyces aquaticus, isolated from submerged decaying wood in freshwater habitats in Guizhou Province, China. Phylogenetic analyses based on a combined dataset of ITS, LSU, SSU, and rpb2 sequence data robustly place Nigrellomyces within the family Pleurotheciaceae (Pleurotheciales, Savoryellomycetidae), with strong statistical support. The genus is currently known only from its asexual morph, which is characterized by macronematous, mononematous, erect, unbranched, septate conidiophores; polyblastic, integrated, terminal or intercalary, sympodial proliferations; denticulate conidiogenous cells with swollen apices; and acrogenous, subglobose to globose, ovoid to obovoid, or ellipsoidal, aseptate, guttulate conidia. Morphological comparisons reveal that Nigrellomyces displays a cordana-like conidiogenesis that is distinct from other genera in Pleurotheciaceae, which typically exhibit acrodictys-, helicoön-, monodictys-, or dactylaria-like asexual morphs. This study provides a comprehensive morphological description, illustrations, and comparative interpretation of the new taxon. An updated phylogenetic backbone tree of Pleurotheciaceae is also presented, improving resolution of intergeneric relationships within the family. The discovery of N. aquaticus not only expands the taxonomic framework of Pleurotheciaceae but also contributes to a deeper understanding of the species richness, ecological roles, and biogeographic distribution of lignicolous freshwater fungi in Southwest China, particularly in the underexplored region of Guizhou Province.

Key words:

Asexual morph, lignicolous freshwater fungi, phylogeny, Sordariomycetes, taxonomy

Introduction

Lignicolous freshwater fungi are a specialized group of fungi that colonize submerged or partially submerged woody substrates across a wide range of freshwater habitats, including streams, rivers, lakes, and reservoirs (Luo et al. 2004; Hyde et al. 2016; Calabon et al. 2022; Calabon et al. 2023). These fungi play an essential ecological role in the degradation of lignocellulosic materials, contributing significantly to the breakdown and recycling of organic matter. Through this decomposition process, they facilitate nutrient release and cycling, thus maintaining the ecological balance and supporting the biodiversity of freshwater ecosystems (Yuen et al. 1998; Bucher et al. 2004; Hyde et al. 2016; Calabon et al. 2023).

In recent decades, Asia has emerged as a global hotspot for lignicolous freshwater fungal research, with numerous studies focusing on the diversity and taxonomy of these fungi (Hyde et al. 2016; Su et al. 2016; Luo et al. 2019; Dong et al. 2020; Bao et al. 2021, 2023; Calabon et al. 2022, 2023; Shen et al. 2022b, 2024; Yang et al. 2023; Wang et al. 2024b; Xu et al. 2025b). In-depth investigations have been conducted, particularly in regions such as Guizhou, Hong Kong, Taiwan, and Yunnan in China, and Chiang Rai and Chiang Mai in Thailand. These regions have yielded a remarkable number of newly described taxa and have significantly expanded our understanding of the diversity and distribution of lignicolous freshwater fungi in tropical and subtropical habitats (Zhang et al. 2011; Jones et al. 2014; Hyde et al. 2016, 2021; Su et al. 2016; Bao et al. 2018, 2019, 2020, 2021, 2023; Luo et al. 2018b, 2019; Dong et al. 2020, 2021a, 2021b; Calabon et al. 2021, 2022, 2023; Shen et al. 2022a, 2022b, 2024; Xu et al. 2023, 2024b, 2025a, 2025b; Yang et al. 2023; Wang et al. 2024a, 2024b; Xiao et al. 2025). Among them, members of the Dothideomycetes and Sordariomycetes dominate lignicolous freshwater fungal communities, with ongoing research continuously revealing new species and higher-order lineages within these two classes (Su et al. 2016; Luo et al. 2019; Dong et al. 2020; Hyde et al. 2021; Calabon et al. 2022). Notably, the families Distoseptisporaceae, Fuscosporellaceae, Pleurotheciaceae, Savoryellaceae, Junewangiaceae, and Sporidesmiaceae of the Sordariomycetes constitute some of the most dominant and diverse groups of lignicolous freshwater fungi, encompassing many major taxa (Luo et al. 2019; Yang et al. 2023; Wang et al. 2024a, 2025; Xu et al. 2025b).

The family Pleurotheciaceae was established by Réblová et al. (2016), with Pleurothecium designated as the type genus. This family encompasses a diverse assemblage of fungi, including several species that inhabit submerged woody substrates in freshwater habitats (Réblová et al. 2016; Luo et al. 2018a; Dong et al. 2021b; Shi et al. 2021; Bao et al. 2022; Huang et al. 2022; Wang et al. 2024a; Xu et al. 2024a, 2025a). Both sexual and asexual morphs of Pleurotheciaceae have been reported, with the sexual morphs characterized by dark, papillate, perithecial, astromatic, immersed to superficial ascomata, unitunicate asci with a distinct non-amyloid apical annulus, and fusiform to ellipsoidal, septate, hyaline ascospores (Réblová et al. 2016; Luo et al. 2018a; Hyde et al. 2020). The asexual morphs of Pleurotheciaceae include species with diverse morphologies, comprising acrodictys-like (Yanna and Hyde 2002; Sadowski et al. 2012), helicoön-like (Dayarathne et al. 2019; Réblová et al. 2020), monodictys-like (Hyde et al. 2020), and dactylaria-like taxa (Réblová et al. 2016; Luo et al. 2018a).

In the latest update of “The 2024 Outline of Fungi and Fungus-like Taxa” compiled by Hyde et al. (2024), a total of 15 genera are accepted within the family Pleurotheciaceae, including Adelosphaeria Réblová, Anapleurothecium Hern.-Restr., R.F. Castañeda & Gené, Coleodictyospora Charles, Dematipyriforma L. Yan Sun, Hai Y. Li, Xiang Sun & L.D. Guo Helicoascotaiwania Dayar., Maharachch. & K.D. Hyde, Melanotrigonum Réblová, Monotosporella S. Hughes, Neomonodictys Y.Z. Lu, C.G. Lin & K.D. Hyde Phaeoisaria Höhn., Phragmocephala E.W. Mason & S. Hughes, Pleurotheciella Réblová, Seifert & J. Fourn., Pleurothecium Höhn., Pseudosaprodesmium X.G. Tian, K.D. Hyde & Tibpromma, Saprodesmium W. Dong & Doilom, and Sterigmatobotrys Oudem. The taxonomic placement of certain genera, particularly Rhexoacrodictys, has remained controversial. Initially, Rhexoacrodictys W.A. Baker & Morgan-Jones was placed in the order Savoryellales by Xia et al. (2017); subsequent molecular phylogenetic analyses by Luo et al. (2019) transferred Rhexoacrodictys to Pleurotheciales. Subsequent phylogenetic studies have confirmed the findings of Luo et al. (2019), providing robust support for the reassignment of Rhexoacrodictys (Dong et al. 2021b; Shi et al. 2021; Bao et al. 2022; Huang et al. 2022; Wang et al. 2024a, 2025).

Despite “The 2024 Outline of Fungi and Fungus-like Taxa” listing this genus under Savoryellaceae (Savoryellales), current phylogenetic evidence clearly indicates that Rhexoacrodictys is best placed in Pleurotheciaceae (Pleurotheciales), and its classification within this family is now widely accepted (Dong et al. 2021b; Shi et al. 2021; Bao et al. 2022; Huang et al. 2022; Wang et al. 2024a, 2025). Furthermore, Obliquifusoideum W. Dong & Doilom was recently included in Pleurotheciaceae by Wang et al. (2024a), based on both morphological characteristics and phylogenetic evidence. In the other study, based on morphological characteristics and DNA sequence data, Saprodesmium was treated as a synonym of Rhexoacrodictys (Wang et al. 2025). To date, the family Pleurotheciaceae comprises sixteen genera and more than 100 species, which are primarily saprobic on a variety of decaying plant substrates in both freshwater and terrestrial habitats (Réblová et al. 2016; Luo et al. 2018a; Dong et al. 2021b; Shi et al. 2021; Bao et al. 2022; Huang et al. 2022; Wang et al. 2024a; Xu et al. 2024a, 2025a).

During a recent investigation of lignicolous freshwater fungi in Guizhou Province, China, a previously undescribed cordana-like species was isolated. Phylogenetic analyses based on a combined dataset of ITS, LSU, SSU, and rpb2 gene regions revealed that the new collection formed a well-supported and distinct clade within the family Pleurotheciaceae. Based on a comprehensive assessment integrating detailed morphological observations and multi-locus phylogenetic evidence, we introduce a new genus to accommodate this unique taxon. This study provides a thorough taxonomic treatment of the new taxa, including detailed morphological descriptions, high-quality illustrations, and comparative analyses with closely related taxa. In addition, an updated phylogenetic backbone tree of Pleurotheciaceae is presented, offering insights into the relationships among genera within the family. Our findings contribute not only to the taxonomic richness of lignicolous freshwater fungi in Guizhou Province but also enhance our broader understanding of fungal diversity associated with freshwater habitats in southwest China.

Materials and methods

Sample collection and specimen examination

Lignicolous substrates (decaying wood) were collected from a stream in Baiyun District, Guiyang City, Guizhou Province, China. Samples were taken to the laboratory in plastic bags and labeled with collection details, including locality, habitat, and date (Rathnayaka et al. 2024). Samples were cultured in plastic boxes lined with moistened tissue at room temperature for 1–2 weeks (Yang et al. 2023). The samples were examined using a stereomicroscope (SMZ 745, Nikon, Japan). Micromorphological characters were captured using a Nikon EOS 90D digital camera attached to an ECLIPSE Ni compound microscope (Nikon, Japan). Measurements of conidiophores, conidiogenous cells, and conidia were carried out using the Tarosoft (R) Image Frame Work program.

Isolation and material deposition

Single-spore isolation was performed following the method described by Senanayake et al. (2020). The germinated conidia were aseptically transferred to fresh potato dextrose agar (PDA; Oxoid, CM0139) and incubated at room temperature for 41 days. Morphological characteristics of the fungal mycelium on PDA, including color, shape, size, margin, and elevation, were documented. Dried fungal specimens were deposited in the Herbarium of Guizhou Academy of Agricultural Sciences (Herb. GZAAS), Guiyang, China. Pure cultures were deposited at the Guizhou Culture Collection (GZCC), Guiyang, China. Descriptions of the new taxa were uploaded to the Faces of Fungi webpage following the guidelines of Jayasiri et al. (2015). The new species were registered in the MycoBank database (https://www.mycobank.org/), and MycoBank numbers were obtained.

DNA extraction, PCR amplification, and sequencing

Fresh fungal mycelia grown on PDA were scraped using sterilized scalpels. Genomic DNA was extracted using the Biospin Fungus Genomic DNA Extraction Kit (BioFlux, China), following the manufacturer’s protocol. The primer pairs ITS5/ITS4 (White et al. 1990), LR0R/LR5 (Vilgalys and Hester 1990), NS1/NS4 (White et al. 1990), and fRPB2-5F/fRPB2-7cR (Liu et al. 1999) were used to amplify the ITS, LSU, SSU, and rpb2 regions, respectively. PCR amplification was performed in a 25 μL reaction volume, consisting of 13.5 μL of 2× Taq PCR Master Mix (China; containing Taq DNA polymerase, dNTPs, MgCl2, and reaction buffer), 1 μL of each primer, 1 μL of template DNA, and 8.5 μL of ddH2O. The polymerase chain reaction (PCR) conditions employed were in accordance with the reaction conditions outlined by Wang et al. (2024a). The PCR products were purified and sequenced by Sangon Biotech (Shanghai, China) Co., Ltd.

Phylogenetic analyses

BioEdit v. 7.0.5.3 (Hall 1999) and SeqMan v. 7.0.0 (Swindell and Plasterer 1997) were used to check and assemble the newly generated sequences. Sequences obtained in this study (Table 1) were deposited in the NCBI GenBank database (https://blast.ncbi.nlm.nih.gov/Blast.cgi). Multiple sequence alignments for each locus dataset were performed using MAFFT v.7.473 (https://mafft.cbrc.jp/alignment/server/, Katoh et al. 2019) and visually inspected in AliView (Larsson 2014). The LSU and ITS alignments were trimmed using trimAl v1.2rev59 (Capella-Gutiérrez et al. 2009) and subsequently merged using SequenceMatrix v1.7.8 (Vaidya et al. 2011).

Table 1.
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Taxa used in this study, along with their corresponding GenBank accession numbers.

Taxon Strain/Specimens GenBank accession numbers
ITS LSU SSU rpb2
Adelosphaeria catenata CBS 138679T KT278721 KT278707 KT278692 KT278743
Anapleurothecium botulisporum FMR 11490T KY853423 KY853483 – –
Canalisporium exiguum SS 00809 GQ390296 GQ390281 GQ390266 HQ446436
Canalisporium grenadoideum SS 03615 – GQ390267 GQ390252 HQ446420
Canalisporium pulchrum SS 03982 GQ390292 GQ390277 GQ390262 HQ446432
Coleodictyospora muriformis MFLUCC 18-1243T MW981642 MW981648 MW981704 –
Coleodictyospora muriformis MFLUCC 18-1279 MW981643 MW981649 MW981705 –
Conioscypha lignicola CBS 335.93 – AY484513 JQ437439 JQ429260
Conioscypha minutispora CBS 137253 – MH878131 – –
Dematipyriforma aquilaria CGMCC 3.17268T KJ138621 KJ138623 KJ138622 –
Dematipyriforma muriformis MFLU 21-0146T OM654773 OM654770 – –
Dematipyriforma nigrospora MFLUCC 21-0096T MZ538524 MZ538558 – –
Dematipyriforma nigrospora MFLUCC 21-0097 MZ538525 MZ538559 MZ538574 MZ567113
Helicoascotaiwania farinosa DAOM 241947 JQ429145 JQ429230 – –
Helicoascotaiwania lacustris CBS 145963T MN699399 MN699430 MN699382 MN704304
Helicoascotaiwania lacustris CBS 146144 MN699401 MN699432 MN699384 MN704306
Melanotrigonum ovale CBS 138743T KT278724 KT278709 KT278696 KT278745
Melanotrigonum ovale CBS 138742 KT278723 KT278708 KT278695 KT278744
Monotosporella setosa HKUCC 3713 – AF132334 – –
Neoascotaiwania fusiformis MFLU 15-1156T MG388215 NG_057114 – –
Neoascotaiwania fusiformis MFLUCC 15-0625 – KX550894 KX550898 –
Neomonodictys aquatica KUNCC 21-10708T MZ686200 OK245417 – –
Neomonodictys muriformis MFLUCC 16-1136T MN644509 MN644485 – –
Nigrellomyces aquaticus GZCC 25-0630T PV871229 PV871235 – PV872880
Nigrellomyces aquaticus GZCC 25-0631 PV871230 PV871236 – PV872881
Obliquifusoideum guttulatum MFLUCC 18-1233T MW981645 MW981650 MW981706 –
Obliquifusoideum triseptatum CGMCC 3.27014T PP445243 PP049503 PP049521 PP068779
Phaeoisaria motuoensis KUNCC 10410T OP626333 OQ947034 OQ947036 –
Phaeoisaria motuoensis KUNCC 10450 OQ947032 OQ947035 OQ947037 –
Phaeoisaria obovata CGMCC 3.27015T PP049488 PP049504 PP049522 PP068788
Phaeoisaria obovata KUNCC 23-15598 PP049489 PP049505 PP049523 PP068784
Phaeoisaria sedimenticola CGMCC3.14949T JQ074237 JQ031561 – –
Phaeoisaria sedimenticola KUNCC 23-14648 PP049490 PP049506 PP049524 PP068783
Phaeoisaria synnematica NFCCI 4479T MK391494 MK391492 – –
Phaeoisaria synnematica KUNCC 23-16619 PP049493 PP049509 PP049527 PP068787
Phragmocephala stemphylioides KAS 4277 KT278730 KT278717 – –
Pleurotheciella aquatica MFLUCC 17-0464T MF399236 MF399253 MF399220 MF401405
Pleurotheciella brachyspora CGMCC 3.25435T OR589321 OR600969 PP049532 PP068773
Pleurotheciella fusiformis MFLUCC 17-0113T MF399233 MF399250 MF399218 MF401403
Pleurotheciella fusiformis MFLUCC 17-0115 MF399232 MF399249 MF399217 MF401402
Pleurotheciella guttulata KUMCC 15-0442 MF399239 MF399256 MF399222 MF401408
Pleurotheciella guttulata KUMCC 15-0296T MF399240 MF399257 MF399223 MF401409
Pleurotheciella longidenticulata CGMCC 3.27018T PP049496 PP049513 PP049531 PP068776
Pleurothecium aquaticum MFLUCC 17-1331T MF399245 MF399263 – –
Pleurothecium aquaticum MFLUCC 21-0148 OM654775 OM654772 OM654807 –
Pleurothecium aquisubtropicum GZCC 21-0670T OM339436 OM339433 – –
Pleurothecium pisiformis KUNCC 24-19085T PV264837 PV264846 PV335238 –
Pleurothecium pulneyense MFLUCC 16-1293 – MF399262 MF399228 MF401414
Pleurothecium semifecundum CBS 131482 JQ429158 JQ429239 JQ429253 –
Pleurothecium semifecundum CBS 131271T JQ429159 JQ429240 JQ429254 JQ429270
Pseudosaprodesmium cocois MFLU 23-0225T OR438401 OR438864 OR458363 –
Pseudosaprodesmium cocois GZAAS 23-0588 OR438402 OR438865 OR458364 –
Rhexoacrodictys fimicola HMAS 43690 KU999957 KX033550 KX033519 –
Rhexoacrodictys fimicola HMAS 47737 KU999960 KX033553 KX033522 –
Rhexoacrodictys fimicola MFLUCC 18-0340 OM654774 OM654771 OM654806 –
Rhexoacrodictys melanospora KUNCC 22-12406T OP168085 OP168087 OP168088 OP208807
Rhexoacrodictys melanospora KUNCC 22-12411 OP168093 OP168101 OP168099 OP208808
Saprodesmium dematiosporium KUMCC 18-0059T MW981646 MW981647 MW981707 –
Sterigmatobotrys macrocarpa PRM 915682 JQ429153 GU017317 JQ429255 –
Sterigmatobotrys rudis DAOM 229838 JQ429152 JQ429241 JQ429256 JQ429272

Note: “T” indicates ex-type strains. Newly generated sequences are in bold black. “-” indicates the unavailable data in GenBank.

Maximum likelihood (ML) analysis was conducted using the IQ-TREE web server (http://iqtree.cibiv.univie.ac.at/) based on Bayesian Information Criteria (BIC) (Nguyen et al. 2015). The substitution model was automatically selected by the server. Bayesian inference (BI) analysis was performed using MrBayes on XSEDE (3.2.7a) via CIPRES Science Gateway (Stamatakis 2014). The aligned FASTA file was converted to NEXUS format using AliView (Larsson 2014). The best-fit evolutionary model for each dataset was determined using MrModeltest v. 2.3.10 (Nylander 2004). The GTR+G+I substitution model was selected for LSU, ITS, and rpb2, whereas the K80+I+G model was chosen for SSU. Posterior probabilities (BYPP) were determined based on Bayesian Markov chain Monte Carlo (BMCMC) sampling (Huelsenbeck and Ronquist 2001). Four simultaneous Markov chains were run for 10,000,000 generations, and trees were sampled every 1,000 generations. The burn-in phase was set at 25%, and the remaining trees were used to calculate posterior probabilities.

Phylogenetic trees were visualized using FigTree v. 1.4.4 and further edited in PowerPoint. The photo plate was prepared using Adobe Photoshop CS6 software (Adobe Systems, USA).

Phylogenetic analysis results

The single-locus and multi-locus phylogenetic analyses (LSU, ITS, SSU, and rpb2) were implemented to elucidate the phylogenetic position of the two new strains. The concatenated sequence matrix comprised 3,102 characters (LSU: 1–826, ITS: 827–1,371, SSU: 1,372–2,143, and rpb2: 2,144–3,102) across 60 taxa. Maximum likelihood (ML) and Bayesian inference (BI) analyses were conducted on the concatenated datasets of LSU, ITS, SSU, and rpb2, both yielding similar tree topologies. Fig. 1 presents the best-scoring ML tree, which had a final log-likelihood value of –25777.951173.

Figure 1. 

Phylogenetic tree generated from ML analysis based on the combined LSU, ITS, SSU, and rpb2 sequence data. Bootstrap support values for maximum likelihood greater than 75% (ML left) and Bayesian posterior probabilities ≥ 0.95 (BYPP right) are shown at the nodes. The tree was rooted with Conioscypha lignicola (CBS 335.93) and C. minutispora (CBS 137253). Ex-type strains are denoted with “T,” and newly isolated strains are in bold red fonts.

Based on the multi-gene phylogenetic tree (Fig. 1), our collections represent a new genus and a novel species within the family Pleurotheciaceae (Pleurotheciales, Sordariomycetes). Our isolates (GZCC 25-0630 and GZCC 25-0631) formed a sister clade to the clade comprising Neomonodictys aquatica (KUNCC 21-10708) and N. muriformis (MFLUCC 16-1136) with weak support.

Taxonomy

Nigrellomyces W.M. Zhang & Q.Y. Feng, gen. nov.

MycoBank No: 904235

Etymology.

“Nigrellomyces” refers to the small, dark-colored conidia characteristic of this genus.

Description.

Saprobic on decaying wood submerged in a freshwater stream. Asexual morph: Colonies superficial, effuse, hairy, brown to black, scattered, with glistening conidial masses at apex. Mycelium partly superficial, partly immersed, consisting of branched, septate, smooth, smooth-walled, hyaline to pale brown hyphae. Conidiophores macronematous, mononematous, solitary, erect, unbranched, septate, straight or flexuous, cylindrical, slightly constricted at septa, dark brown, becoming pale brown to brown towards the apex. Conidiogenous cells polyblastic, integrated, terminal or intercalary sympodial proliferations, sometimes denticles, cylindrical, reniform, swollen at the top, pale brown to brown. Conidia acrogenous, subglobose to globose, ovoid to obovoid, or ellipsoidal, aseptate, occasionally forming chains in water, guttulate, subhyaline to brown or black, smooth-walled. Sexual morph: Undetermined.

Type species.

Nigrellomyces aquaticus W.M. Zhang & Q.Y. Feng

Notes.

Morphologically, Nigrellomyces can be readily distinguished from other genera in Pleurotheciaceae by its polyblastic, reniform conidiogenous cells with curved apices and subglobose to globose, ovoid to obovoid, or ellipsoidal, aseptate conidia that occasionally form chains in water. Phylogenetically, Nigrellomyces forms a distinct clade within Pleurotheciaceae, supporting its recognition as a new genus. Herein, we establish the genus Nigrellomyces to accommodate a new species, N. aquaticus, which is designated as the type species based on both molecular evidence and its distinctive conidial morphology.

Nigrellomyces aquaticus W.M. Zhang & Q.Y. Feng, sp. nov.

MycoBank No: 904236
Fig. 2

Etymology.

“aquaticus’’ refers to the aquatic habitat of this fungus.

Figure 2. 

Nigrellomyces aquaticus (GZAAS 25-0660, holotype). a, b. Colonies on the host surface; c–f. Conidiophores, conidiogenous cells, and conidia; g–h. Conidiogenous cells; i-j. Conidiogenous cells and conidia; k. Germinated conidium; l–o. Conidia; p, q. Colonies on PDA from above and below after 41 days of incubation at room temperature. Scale bars: 60 μm (d–f); 50 μm (c); 20 μm (g–j); 10 μm (k–o).

Holotype.

GZAAS 25-0660

Description.

Saprobic on decaying wood submerged in a freshwater stream. Asexual morph: Colonies superficial, effuse, hairy, brown to black, scattered, with glistening conidial masses at apex. Mycelium partly superficial, partly immersed, consisting of branched, septate, smooth, smooth-walled, hyaline to pale brown hyphae. Conidiophores macronematous, mononematous, solitary, erect, unbranched, multi-septate, straight, or flexuous, cylindrical, slightly constricted at septa, 146–364 × 4.5–8 μm x ̄ = 224 × 5.8 μm, n = 25), dark brown, becoming pale brown to brown towards the apex. Conidiogenous cells polyblastic, integrated, terminal or intercalary, sympodial proliferations, sometimes denticles, cylindrical, reniform, curved, and swollen at the apex, 8.5–28 × 4–6 μm x ̄ = 20 × 5.2 μm, n = 25), pale brown to brown. Conidia acrogenous, subglobose to globose, ovoid to obovoid, or ellipsoidal, aseptate, occasionally forming chains in water, guttulate, 7.5–12.5 × 5–8.5 μm x ̄ = 8.9 × 7 μm, n = 25), light brown or black, smooth-walled, sometimes have small apiculus at the base. Sexual morph: Undetermined.

Culture characteristics.

Conidia germinate on PDA within 17 hours, producing germ tubes from the conidial body. Colonies on PDA are irregular with a flat surface and undulate margin, reaching 38 cm in diameter after 41 days at room temperature (approximately 25 °C), and are brown to dark brown on both the surface and reverse sides.

Material examined.

China • Guizhou Province, Guiyang City, Baiyun District, Changpo Ling National Forest Park, on rotting wood in a freshwater habitat, 15 March 2025, Wang-Ming Zhang, QX13 (GZAAS 25-0660, holotype), ex-type living cultures GZCC 25-0630; • Ibid., QX13.1 (GZAAS 25-0661, paratype), living culture GZCC 25-0631.

Notes.

In our phylogenetic tree (Fig. 1), isolates (GZCC 25-0630 and GZCC 25-0631) formed a sister clade to Neomonodictys aquatica (KUNCC 21-10708) and N. muriformis (MFLUCC 16-1136) with weak support. Nigrellomyces aquaticus (GZAAS 25-0660) can be distinguished from Neomonodictys aquatica (KUN-HKAS 115806) and N. muriformis (MFLU 17-1178) by its longer conidiophores, elongated, polyblastic conidiogenous cells, and aseptate conidia (Hyde et al. 2020; Huang et al. 2022). Moreover, base pair comparison of Nigrellomyces aquaticus (GZCC 25-0630) and N. muriformis (MFLUCC 16-1136) shows 96/588 bp differences in ITS (16.3%, gaps 37 bp) and 22/829 bp differences in LSU (2.7%, gap one bp). Therefore, based on multigene phylogenetic analysis and morphological differences, we introduce Nigrellomyces aquaticus as a novel genus and species.

Discussion

The newly introduced genus Nigrellomyces shares morphological similarities with Cordana, including brown, septate conidiophores; polyblastic, swollen conidiogenous cells; and brown, obovoid to ellipsoidal conidia (Hughes 1955; Hernández-Restrepo et al. 2014; Hernandez Restrepo et al. 2015; Kuo et al. 2024; Xu et al. 2024b). However, Nigrellomyces differs from Cordana in several key features. Notably, its conidiogenous cells are curved at the apex and occasionally bear denticles, while its conidia are aseptate, in contrast to the typically septate conidia of Cordana (Hughes 1955; Hernández-Restrepo et al. 2014; Hernandez Restrepo et al. 2015; Kuo et al. 2024; Xu et al. 2024b). In addition to these morphological distinctions, the two genera are phylogenetically unrelated. Cordana is classified within the family Cordanaceae (Coniochaetales, Sordariomycetidae), whereas Nigrellomyces is placed in Pleurotheciaceae (Pleurotheciales, Savoryellomycetidae). Our multilocus phylogenetic analysis revealed that Nigrellomyces forms a monophyletic clade with strong support, positioned as a sister group to Neomonodictys within Pleurotheciaceae. Morphologically, Nigrellomyces is distinct from other genera in the family. While most members of Pleurotheciaceae exhibit acrodictys-like (Yanna and Hyde 2002; Sadowski et al. 2012), helicoön-like (Dayarathne et al. 2019; Réblová et al. 2020), monodictys-like (Hyde et al. 2020), and dactylaria-like (Réblová et al. 2016; Luo et al. 2018a) asexual morphs, Nigrellomyces displays unique cordana-like characters. Given its morphological and phylogenetic uniqueness, Nigrellomyces is established here as a new genus to accommodate this newly discovered taxon.

Additional information

Conflict of interest

The authors have declared that no competing interests exist.

Ethical statement

No ethical statement was reported.

Use of AI

No use of AI was reported.

Funding

This work was supported by the Doctoral Research Fund of Beijing Jishuitan Hospital Guizhou Hospital (grant number JGYBS[2025]01) and the Medical Research Union Fund for High-quality Health Development of Guizhou Province (grant number 2024GZYXKYJJXM0151).

Author contributions

Writing - original draft: XS, WZ. Writing - review and editing: QF, XZ, WX, JL.

Data availability

All of the data that support the findings of this study are available in the main text.

References

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