Pseudoleptodontidium Thitla, Monkai, Lumyong & Hongsanan 2025, gen. nov.

Pseudoleptodontidium Thitla, Monkai, Lumyong & Hongsanan gen. nov. Etymology. The name refers to its morphological similarity to Leptodontidium. Classification. Sordariomycetes, Xylariomycetidae, Amphisphaeriales, incertae sedis. Asexual morph: Mycelium composed of hyaline to black, thin- to thick-walled, smooth, branched, septate. Conidiophores arising from hyphae, solitary, erect, cylindrical, pale brown to dark brown, thick-walled, occasionally roughened on lower part, septate. Conidiogenous cells terminal and intercalary on conidiophores, occasionally lateral on hyphae, obclavate, sympodially proliferate, denticulate, hyaline to pale brown, smooth, septate. Conidia hyaline, smooth, aseptate, subglobose to ellipsoidal, slightly curved. Chlamydospores solitary, terminal on hyphae, medium brown to dark brown, smooth, thick-walled, aseptate, subglobose. Sexual morph: absent. Type species. Pseudoleptodontidium chiangmaiense Thitla, Monkai, Lumyong & Hongsanan, sp. nov. Notes. Hernández-Restrepo et al. (2017) established Leptodontidium in Leptodontidiaceae (Helotiales, Leotiomycetes), characterised by erect conidiophores and conidiogenous cells with a long rachis bearing denticles, as well as the presence of a Beauveria - like synasexual morph. Neoleptodontidium was introduced by Crous et al. (2023) due to its morphological resemblance to Leptodontidium, but it differs in having minute, terminal and lateral exophiala-like phialides. Based on LSU phylogeny, the type species of Neoleptodontidium (N. aquaticum) clustered with Leptodontidium aciculare (Crous et al. 2023). Hence, Crous et al. (2023) transferred L. aciculare to Neoleptodontidium as N. aciculare by the morphological and phylogenetic congruence. Pseudoleptodontidium is morphologically similar to Neoleptodontidium, sharing septate, subcylindrical conidiophores, terminal and lateral phialidic conidiogenous cells and aseptate subcylindrical conidia (Crous et al. 2023). However, Pseudoleptodontidium can be distinguished from Neoleptodontidium by its obclavate, sympodially proliferating, denticulate conidiogenous cells and subglobose to ellipsoidal conidia. The phylogeny, based on a combined ITS, LSU, RPB 2 and TUB dataset, revealed that Pseudoleptodontidium forms an independent lineage, sister to Neoleptodontidium with significant support (BS 96 % ML and PP 1.00; Fig. 4). Although Crous et al. (2023) placed Neoleptodontidium in Xylariales genera incertae sedis, our phylogeny indicates that Pseudoleptodontidium and Neoleptodontidium are closely related to the Amphisphaeriaceae, Cylidriaceae, Phlogicylindriaceae and Amphisphaeriales genera incertae sedis (Neoarthrinium, Pidoplitchkoviella) (Fig. 4). Therefore, due to their distinct morphology and phylogeny, Pseudoleptodontidium is introduced as a genus incertae sedis in Amphisphaeriales, with Ps. chiangmaiense designated as the type species.