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

Ophiostoma querceti H. G. Woo, D. Hyeon Lee & S. E. Cho sp. nov. Fig. 3 Etymology. The specific epithet querceti refers to the oak stand (quercetum) from which the type isolate was isolated. Type. Republic of Korea • Gyeongsangnam-do, Sancheong-gun, Danseong-myeon, Baegun-ri, Mt. 254; 35°16'44.0"N, 127°51'24.0"E. Wounds, Quercus mongolica. 13 May 2025. D. Hyeon Lee. CDH 138 (Holotype. KA 25-1572, ex-holotype culture KACC 411103). 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, (97 –) 111–182 (– 228) µm diam; ornamented with brown hyphal hairs (140 –) 175–187 (– 200) μm long. Ascomatal necks black, straight or slightly curved, (350 –) 515–650 (– 700) µm long, (23 –) 28.0–32.7 (– 35) µm wide at base, (5.5 –) 8.31–9.48 (– 10.0) µm wide at the apex. Ostiolar hyphae hyaline, divergent, non-septate, (20 –) 25–40 (– 45) µm long. Asci not observed. Ascospores hyaline, 1 - celled, no sheath, allantoid, cylindrical and slightly curved, (2.5 –) 3–4 (– 4.5) × 1–1.5 (– 2) 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, (215 –) 278–323 (– 340) µm long, (29.2 –) 36.1–40.7 (– 43) µm wide at base; conidiogenous cells annellated, discrete, terminal or intercalary, cylindrical, tapering towards apex, hyaline, smooth, (34.9 –) 47.0–57.6 (– 60) µm; conidia hyaline, 1 - celled, smooth, oblong, in some cases clavate, (3.1 –) 3.8–4.7 × (1.4 –) 1.6–1.9 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°16'44.0"N, 127°51'24.0"E. Wounds, Quercus mongolica. 13 May 2025. D. Hyeon Lee. (CDH 138-1). Habitat. Fresh wounds (less than one-month-old) on Quercus mongolica trees. Notes. Ophiostoma querceti is phylogenetically closely related to O. quercus. While they share similarities in overall morphology, they exhibit clear differences in culture growth rates and perithecial neck lengths. Culturally, O. querceti grows slowly, reaching only 23 mm in diameter in 10 days at 20–25 ° C, which distinctly differentiates it from O. quercus, a species that grows much faster, reaching between 41.1 and 57.4 mm in 10 days at 25 ° C. Furthermore, O. querceti produces relatively short perithecial necks (350–700 μm), whereas O. quercus often develops significantly longer perithecial necks that can reach up to 2,036 μm. Both species produce similarly sized ascospores, though the allantoid, slightly curved ascospores of O. querceti (2.5–4.5 × 1.0–2.0 μm) differ slightly from the reniform to allantoid ascospores typically observed in O. quercus (2.6–4.8 × 0.9–2.4 μm) (Grobbelaar et al. 2009).