Corynascus fluvialis Bhagya, Phukhams., K. D. Hyde & E. B. G. Jones 2026, sp. nov.

Corynascus fluvialis Bhagya, Phukhams., K. D. Hyde & E. B. G. Jones sp. nov. Fig. 5 Etymology. Based on the habitat of the host. Holotype. MFLU 25-0196. Description. Saprobic on dead, moist, decaying stems of Carex sp. Sexual morph: Ascomata 110–150 (x ̄ = 124 μm, n = 5), cleistothecial, scattered, loosely aggregated or gregarious, superficial on host surface, dark brown, to black or olivaceous, globose to subglobose, smooth, and coriaceous. Peridium 1–3 μm (x ̄ = 1.5 μm, n = 5) composed of olivaceous brown cells in textura epidermoidea. Paraphyses 12–25 × 1–2.5 μm (x ̄ = 18.5 × 1.5 μm, n = 5), filiform, aseptate, hyaline, shorter than the asci. Asci 25–38 × 22–35 μm (x ̄ = 35 × 28 μm, n = 10), 8 - spored, unitunicate, globose or subglobose to pyriform or broadly clavate, thin-walled, caudate with short cylindrical to angular pedicel, evanescent. Ascospores 12–18 × 6–10 μm (x ̄ = 14.5 × 8.5 μm, n = 30), overlapping, biseriate to triseriate or variably arranged, ellipsoidal or broadly fusiform, straight, aseptate, hyaline when immature, olivaceous-green when mature, thick, smooth-walled, pointed towered end, with one germ pore at apex. Asexual morph: undetermined. Culture characteristics. Ascospore germinating on malt extract agar (MEA) within 72 h. Germ tubes are produced from the apical ends of the ascospores. Colonies growing on MEA, reaching 20 mm in 4 weeks at 25 ° C. Mycelia superficial, umbonate with a complete edge, from above light grey at the canter, off white to hyaline towards edge, from reverse dark greenish ash from the canter surrounded with off-white ring at the edge. Material examined. Thailand • Prachuap Khiri Khan Province, Pran Buri District, Pranburi river, on decaying leaf of Carex sp. (Cyperaceae), 25 August 2023, Tharindu Bhagya, TB 130 (MFLU 25-0196, holotype); ex-type living culture (MFLUCC 25-0235); ibid., TB 130 B (MFLU 25-0197). GenBank numbers. MFLU 25-0196: ITS = PV 764283, rpb 2 = PV 799940, tef 1 - α = PV 799942; MFLU 25-0197: ITS = PV 764282, rpb 2 = PV 799941. Notes. The newly isolated strain (MFLUCC 25-0235) clustered with Corynascus novoguineensis (CBS 359.72 and NBRC 9556) with 89 % ML and 0.90 BYPP support (Fig. 2). Strain MFLUCC 25-0235 shares common characteristics with Corynascus, including cleistothecial ascomata, a peridium composed of cells in textura epidermoidea, and fusiform ascospores (Marin-Felix et al. 2015; Crous et al. 2016). Phylogenetically, the new strain differs from the type strain of C. novoguineensis (CBS 359.72) by 2.8 % in ITS, 3.2 % in tef 1 - α, and 4.4 % in rpb 2 in pairwise comparisons, excluding gaps. Morphologically, the new isolate is distinguishable from C. novoguineensis (CBS 359.72 and NBRC 9556) by possessing a smooth ascomatal wall, asci with cylindrical to angular pedicel and hyaline immature ascospores that change to olivaceous-green at maturity (Fig. 5). In comparison, C. novoguineensis (CBS 359.72 and NBRC 9556) develops a verrucous ascomatal wall and pinkish immature ascospores. The presence of hyaline, filiform paraphyses makes the new isolate unique among related taxa in the genus Corynascus (Marin-Felix et al. 2015; Crous et al. 2016). Considering the available morphological and phylogenetic evidence, we introduce C. fluvialis (MFLUCC 25-0235) as a new species from freshwater wetlands in Thailand.