Nigrellomyces aquaticus W. M. Zhang & Q. Y. Feng 2025, sp. nov.

Nigrellomyces aquaticus W. M. Zhang & Q. Y. Feng sp. nov. Fig. 2 Etymology. “ aquaticus ’’ refers to the aquatic habitat of this fungus. 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, QX 13 (GZAAS 25-0660, holotype), ex-type living cultures GZCC 25-0630; • Ibid., QX 13.1 (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.