Muciflexus inthanonensis V. S. Silva, K. D. Hyde & Jayaward., 2025

Muciflexus inthanonensis V. S. Silva, K. D. Hyde & Jayaward. sp. nov.

Fig. 1 View Figure 1

Holotype.

MFLU 24–0382 View Materials .

Etymology.

” inthanonensis ” refers to the type locality, Doi Inthanon, Thailand.

Description.

Saprobic on a leaf of a fallen unknown broadleaf species. Sexual morph: Undetermined. Asexual morph: Hyphomycetous, erect, appear in solitary or in groups. Surface mycelium composed of branched, hyaline, smooth-walled hyphae. Conidiophores erect, simple or occasionally branched, straight to flexuous, arranged in dense clusters or solitary, arising directly from hyphae, with 0–1 basal septa, cylindrical, slightly tapering towards the apical end, hyaline, smooth-walled, 19.5–85 (x ̄ = 55.3, n = 10) µm, base 2.2–3.2 (x ̄ = 2.6, n = 10) µm, apex 1.3–1.9 (x ̄ = 1.5, n = 10) µm. Conidiogenous cells integrated, apically produce 1–4 conidia, adhering in slimy masses. Conidia solitary or occasionally grouped, straight to slightly curved, often aseptate or 1 - septate or rarely 2–3 septate, granular, fusoid, apex obtuse, base truncate, hyaline, smooth-walled, 10.5–19 (x ̄ = 13.9, n = 68) × 2.1–3.3 (x ̄ = 2.7, n = 68) µm, L / W 5.14.

Culture characteristics.

In both PDA and MEA media, culture diameter reaches an average of 6 mm within 5 days. On both media, colonies are flat. After about 45 days on the PDA media in the front, it develops in the buff with sparse white aerial mycelium at the centre. On the reverse also, it develops into buff with a smooth, entire margin. On the MEA media in front view, it develops into sparse mycelium white at the centre with an orangish margin ring extending to white aerial mycelium. On the reverse, it is buff and concentric rings gradually becoming light.

Material examined.

Thailand • Chiang Mai Province, Doi Inthanon National Park , on a fallen unidentified broadleaf species, 30 November 2022, V. S. Hittanadurage Silva, V 046 (holotype MFLU 24–0382 View Materials ); ex-type living culture ( MFULCC 24–0502 ) .

GenBank accession numbers.

ITS: PQ 528132, LSU: PQ 528133, SSU: PQ 528134, rpb 2: PQ 590309, tef 1 – α: PQ 568247.

In the phylogenetic tree, the dataset comprised 58 strains representing Niessliaceae , including incertae sedis taxa. Following Hou et al. (2023), taxa with the species name, which are not yet formally accepted or validated under the International Code of Nomenclature for fungi, were also included. They are represented within “ ”. The outgroup is represented by four taxa from Nothoacremoniaceae ( CBS 416.68 , CBS 190.70 , CBS 587.73 , and CBS 397.70 ). The final concatenated nucleotide alignment was composed of ITS, LSU, rpb 2, and tef 1 – α with 2974 sites in total (ITS = 1–569; LSU = 570–1410; rpb 2 = 1411–2166; tef 1 – α = 2167–2974). The maximum likelihood and Bayesian analyses yielded similar tree topologies, which are combined in Fig. 2 View Figure 2 . The maximum likelihood tree default setting in the IQ-TREE web server was used, and for the BI tree, the combined region run quality was checked using Tracer v 1.7. 2 after the runs were completed. All runs were conducted with effective sample size (ESS) values for all parameters. The alignment contained 1,340 unique sites (ITS = 357; LSU = 273; rpb 2 = 406; tef 1 – α = 304).

Notes.

Hou et al. (2023) conducted phylogenetic analyses identifying two distinct clades (Clade G & Clade H) within the family Niessliaceae . The authors highlighted that the phylogenetic relationships within Niessliaceae remain unresolved, with several genera, viz., Niesslia , Cylindromonium , and Trichonectria , exhibiting polyphyletic characteristics ( Hou et al. 2023).

In our analysis, Muciflexus inthanonensis clustered within H. Niessliaceae ( Hou et al. 2023) , alongside taxa from Cylindromonium , Trichonectria , and Phialoseptomonium . However, Trichonectria is currently classified as Hypocreales genera incertae sedis ( Perera et al. 2023; Hyde et al. 2024). Muciflexus inthanonensis formed a sister clade to Trichonectria setadpressa , with a BYPP of 0.98 and MLBS of 89 % statistical support. The noticeable branch length difference suggests that M. inthanonensis forms a distinct lineage, which may be attributed to the inclusion of two additional gene regions (rpb 2 and tef 1 – α) not available for T. setadpressa and potential genetic novelty. Morphologically, T. setadpressa is characterised by sporodochia-like conidiomata with subglobose to broadly ellipsoidal conidia as its asexual morph ( Flakus et al. 2019), whereas M. inthanonensis produces clusters of simple or occasionally branched conidiophores with fusoid conidia. Additionally, Trichonectria is a lichenicolous genus ( Perera et al. 2023), while M. inthanonensis is saprobic, found on a fallen unidentified broadleaf species. Furthermore, a pairwise comparison of all gene regions between M. inthanonensis and T. setadpressa (Table 2 View Table 2 ) provides further evidence supporting the genetic distinctiveness of the newly introduced genus.

Morphologically, Muciflexus inthanonensis closely resembles Phialoseptomonium , particularly in spore characteristics. Its solitary fusoid conidia, which are granular, hyaline, smooth-walled, and adhere in slimy masses, are similar to those of Phialoseptomonium ( Crous et al. 2019 a) . However, M. inthanonensis can be distinguished by its aseptate or 1–3 - septate, grouped conidia and comparatively smaller spore size ( P. eucalypti : L / W = 6.7, P. junci : L / W = 6.2, M. inthanonensis : L / W = 5.14). Phylogenetically, M. inthanonensis clusters distantly from Phialoseptomonium . While Phialoseptomonium species have been reported as saprobes, taxonomic differentiation based on genetic data is also crucial. According to Raja et al. 2017, variation in the LSU gene region is indicative of differences at intermediate taxonomic levels, such as family and genus. Pairwise comparisons between M. inthanonensis and Phialoseptomonium species (Table 2 View Table 2 ) further support the likelihood that M. inthanonensis does not belong to the same genus.

Cylindromonium exhibits polyphyletic behaviour and was established to accommodate Acremonium - like taxa characterised by unbranched, hyaline conidiophores and cylindrical conidia ( Crous et al. 2019 b). Apart from C. alloxyli and C. eugeniicola , the remaining members of the genus are lichenicolous (Suppl. material 2). Cylindromonium alloxyli is mycophilic on Meliola and was found on Alloxylon pinnatum leaves ( Crous et al. 2020), whereas C. eugeniicola is saprobic on leaves ( Crous et al. 2019). Crous et al. 2019 b mentioned the morphological resemblance between Cylindromonium and Phialoseptomonium ; however, they can be distinguished by the cylindrical conidia of Cylindromonium . Based on this, pairwise genetic distances were calculated among all Cylindromonium and Phialoseptomonium species (Suppl. material 3), with the resulting p - distance values presented in Table 3 View Table 3 . These values were then compared against the p - distance values of Muciflexus inthanonensis with both Cylindromonium and Phialoseptomonium , yielding the following results: ITS: 0.14–0.19, LSU: 0.12–0.06, tef 1 – α: 0.12–0.15, and rpb 2: 0.31–0.40. These values fall within or exceed the range that differentiates Cylindromonium and Phialoseptomonium . Additionally, Muciflexus can be morphologically distinguished from Cylindromonium by its occasionally branched conidiophores and fusoid, occasionally grouped conidia. These combined morphological and phylogenetic differences provide strong support for the novelty of the proposed genus.

Based on these host associations along with morphological and phylogenetic evidence, it is inconclusive to place Muciflexus inthanonensis in any of the genera within the H clade of Niessliaceae ( Hou et al. 2023) . Therefore, here we propose a new genus, Muciflexus , to accommodate Muciflexus inthanonensis .