Westerdykella formosana K. W. Cheng & H. A. Ariyaw. 2025, sp. nov.

Westerdykella formosana K. W. Cheng & H. A. Ariyaw. sp. nov. Fig. 16 Typification. TAIWAN • Wanrung Township, Hualien County, 23°42'40.3"N, 121°24'48.2"E, serpentine soil in rice field, 2 nd November 2022, K. W Cheng, holotype, NTUPPMH 22-218 (Permanently preserved in a metabolically inactive state), ex-holotype NTUPPMCC 22-255, ex-isotype NTUPPMCC 22-256 to 259. Etymology. Named after Formosa, the former name of Taiwan, where the type specimen was collected. Description. Sexual morph Cleistothecia 250–430 µm diam, non-ostiolate, globose, glabrous, mostly superficial, some submerged in PDA, dirty gray when immature, black when mature. Peridium single-layered, brown, translucent, membranous, angular cells. Asci subglobose to globose, hyaline when immature, 32 - spored, 15.7–21.0 µm × 14.6–18.4 µm (x ̄ = 18.3 × 16.3 µm, L / W ratio = 1.1, n = 30). Ascospores ellipsoidal, smooth, subhyaline to light brown, 1 to 3 guttules, no germ-slits, 3.4–6.4 µm × 1.8–3.2 µm (x ̄ = 5.2 × 2.6 µm, L / W ratio = 2.01, n = 50). Asexual morph undetermined. Culture characteristics. Colony exhibits rapid growth, reaching 80 mm diam with flat, sparse aerial mycelium, creamy white, surface and margins smooth, pale gray in central region due to the presence of cleistothecia. Notes. Westerdykella formosana forms a distinct clade in our phylogenetic analysis (Fig. 13 and Suppl. material 2: figs S 1, S 2). The ex-type strain of W. formosana (NTUPPMCC 22-255) exhibits significant genetic divergence from its closest relative, the ex-type strain of W. aquatica (JAUCC 1788), with 94.7 % identity in the ITS region (392 / 414 bp, including 1 gap), and from the representative strain PY 1 of W. aquatica in the tub 2 gene (96.7 % identity; 857 / 886 bp). Morphologically, W. formosana produces larger asci but smaller ascospores compared to its phylogenetically closest relative, W. aquatica (x ̄ = 18.3 × 16.3 µm versus 15.3 × 14.1 µm; x ̄ = 5.2 × 2.6 µm versus 6.5 × 2.9 µm). Additionally, W. formosana lacks the yellow hue observed in PDA cultures of W. aquatica (Fig. 16; Song et al. 2020). Based on molecular, morphological, and cultural differences, we propose our five strains (NTUPPMCC 22-255 to 22-259) as a novel species, Westerdykella formosana. Further morphological comparisons with other Westerdykella species are provided in Suppl. material 1: table S 4.