Ophiostoma subcorticale H. G. Woo, D. Hyeon Lee & S. E. Cho 2026, sp. nov.

Ophiostoma subcorticale H. G. Woo, D. Hyeon Lee & S. E. Cho sp. nov. Fig. 5 Etymology. The specific epithet subcorticale is derived from the Latin sub - (under), cortex (bark), and the adjectival suffix - ale (pertaining to), referring to its subcortical habitat. Type. Republic of Korea • Gyeongsangnam-do, Sancheong-gun, Danseong-myeon, Baegun-ri, Mt. 254; 35°16'42.0"N, 127°51'45.0"E. Wounds, Quercus acutissima. 29 Oct. 2025. D. Hyeon Lee. CDH 242 (Holotype. KA 26-0017, ex-holotype culture KACC 411342). Description. Colonies hyaline at first, becoming dark brown in center with age. Mycelium appressed with scarce aerial. Colonies slow growing, reaching 23 mm diam in 10 d at 20–25 ° C. Optimal temperature for growth 20–25 ° C. Ascomata abundantly developing after 14 d on malt extract agar: superficial or partly embedded on media. Bases dark, globose, (120 –) 141.1–158.7 (– 165) µm diam; ornamented with brown hyphal hairs. Ascomatal necks black, straight or slightly curved, (416.7 –) 438.7–460.6 (– 584) µm long, (18 –) 22.0–24.1 (– 25) µm wide at base, (7.6 –) 8.26–8.43 (– 8.7) µm wide at the apex. Ostiolar hyphae hyaline, divergent, non-septate, (15 –) 20–30 (– 35) μm long. Asci not observed. Ascospores hyaline, 1 - celled, no sheath, narrowly ellipsoidal, (3.8 –) 4.60–4.95 (– 5.2) × (2.0 –) 2.21–2.30 (– 2.4) µm accumulated in a cream-white mass at the tip of the neck. Asexual morph synnematous, pesotum-like macronematous, erect, hyaline, pigmented at the base, (185 –) 212.1–228.2 (– 240) µm long, (34 –) 37.8–39.7 (– 42) µm wide at base; conidiogenous cells annellated, discrete, terminal or intercalary, cylindrical, tapering towards apex, hyaline, smooth, (15 –) 23.0–28.2 (– 30) µm; conidia ellipsoidal to subglobose, guttulate (3.0 –) 3.78–4.34 (– 4.6) × (1.5 –) 1.89–2.17 (– 2.3) µm, aggregating into a cream-white mucilaginous spore drop. Additional specimen examined. Republic of Korea • Gyeongsangnam-do, Sancheong-gun, Danseong-myeon, Baegun-ri, Mt. 254; 35°16'42.0"N, 127°51'45.0"E. Wounds, Quercus acutissima. 29 Oct. 2025. D. Hyeon Lee. (CDH 242-1). Habitat. Fresh wounds (less than one-month-old) on Quercus acutissima trees. Notes. Although O. subcorticale is phylogenetically closely related to O. quercus, distinct morphological and cultural differences are evident between the two species. Culturally, both form colonies that become dark brown in the center with age; however, O. subcorticale grows slowly at an optimal temperature of 20–25 ° C. This contrasts sharply with O. quercus, which exhibits a rapid growth rate, reaching 41.1–57.4 mm in diameter within 10 days at 25 ° C. Morphologically, O. subcorticale produces narrowly ellipsoidal ascospores (3.8–5.2 × 2.0–2.4 μm), distinguishing it from O. quercus, which typically produces reniform to allantoid ascospores that are slightly shorter in length (2.6–4.8 × 0.9–2.4 μm). Furthermore, differences can be observed in their asexual morphs: O. subcorticale has ellipsoidal to subglobose conidia (3.0–4.6 × 1.5–2.3 μm), whereas O. quercus predominantly produces elliptical to oblong-obovoid conidia that often feature a distinctly truncate or obtuse base (Grobbelaar et al. 2009).