Helvellosebacina koreana H. Suh, D. Kim & Y. W. Lim 2026, sp. nov.

Helvellosebacina koreana H. Suh, D. Kim & Y. W. Lim sp. nov. Fig. 4 Diagnosis. Basidiomata are fully resupinate on the ground with a smooth and chalky surface. Holotype. REPUBLIC OF KOREA, Gangwon State, Taebaek-si, Danggol-ro, Mt. Taebaek National Park, on a litter soil under dead Pinus densiflora, 05 October 2023, SFC 20231005-04 (dried specimen). Etymology. From the country of origin of the species, the Republic of Korea. Description. Basidiomata fully resupinate, attached firmly to the substrate, litter, and plant materials on the ground. Surface smooth, dull, chalk-white (5 A 2) to apricot (5 A 3), consistency cartilaginous, chalky texture. Margin irregularly thinning out, white to brownish, indistinctly bounded. Basal hyphal system monomitic, subicular hyphae thin-walled up to 0.6 μm, septate with frequent branching, hyaline, without clamp connections, 2.0–3.4 μm thick. Basidiospores elliptical or allantoid, occasionally germinating by repetition, hyaline, smooth, IKI-, CB-, (7.4 –) 8.2–11.8 (– 12.7) × (6.1 –) 6.4–8.4 (– 8.5) μm (L = 10.2 μm, W = 7.2 μm, Q = 1.4, n = 55 / 1). Dikaryophyses simple-structured, sparingly ramified, derived from the same hyphae with basidia. Probasidia elliptical to subglobose or pyriform, mature basidia subglobose, longitudinally septate, 14.6–17.0 × 8.0–10.8 μm, usually containing oil drops with four elongated sterigmata, average 2.4 μm width, up to 19 μm long, blunt at the apex. Cystidia absent. Distribution. REPUBLIC OF KOREA. Additional specimen examined. REPUBLIC OF KOREA, Gangwon State, Mt. Taebaek National Park, Baekcheon Valley, SFC 20231028-04. Notes. Phylogenetically, H. koreana forms a sister clade with two undescribed phylotypes, Helvellosebacina pt. 3 (F 1143128) and pt. 4 (F 1143539), both originating from North Carolina, United States. Compared to H. chrysallidodoma, H. koreana is observed only as a chalky white residue on the ground, apparently representing an early developmental stage that has not yet formed fully developed basidiomata. GenBank accession numbers. ITS (PV 399955, PV 399957), LSU (PV 399917, PV 399919), rpb 2 (PV 417269 – PV 417270).