Saccosoma megasporum Contr.-Pach., Moyao & Garibay-Orijel, 2025

Contreras-Pacheco, Magdalena, Argüelles-Moyao, Andrés, Viurcos-Martínez, Gala A. & Garibay-Orijel, Roberto, 2025, Saccosoma megasporum sp. nov. from a Mexican Abies religiosa forest, Phytotaxa 694 (1), pp. 101-108 : 105-106

Saccosoma megasporum Contr.-Pach., Moyao & Garibay-Orijel sp. nov. FIG. 2

MycoBank number: MB 832474

Etymology: — megasporum (gr. megas = big; gr. sporum = spore, neutral form) epithet refers to the large-sized basidiospores.

HOLOTYPE:— Mexico: Estado de Mexico, Ocoyoacac municipality, El Zarco, km 32.5, August 2, 2012, Contreras 480 ( MEXU 28247 ). GenBank: nucLSU MK733279 ; ITS PP981525.

Diagnosis: — Saccosoma megasporum differs from the rest of Saccosoma species by its large subglobose basidiospores (12–15 × 15–17 µm; Q = 1.14). Similar species are S. globisporum and S. album with smaller basidiospores (8.5–11.5 × 9–12.5 µm; Q = 1.07) and (7–9 × 10–15; Q = 1.56) respectively.

Description:—BASIDIOME resupinate, easily separable from the substrate, hypochnoid, 10 × 27 mm, 0.2–0.3 mm thick, whitish (1 A 1). Hymenophore smooth to slightly papillated. Margin indeterminate and fibrillose. HYPHAL SYSTEM monomitic with generative hyphae and clamp connections, slightly thickened walls (0.5 µm), hyphae 4–5 µm diam, hyaline. Subicular hyphae loosely arranged, thin to slightly thick walled. PROBASIDIA clavate 12–20 × 48–63 µm, with refractive content, thin-walled. BASIDIA, 10 × 50–70 µm, four-celled, tubular, with refractive contents, thin-walled, with acicular sterigmata that arise from each basidial cell in the most apical portion 5–12 µm long. BASIDIOSPORES subglobose 12–15 × 15–17 µm (Mean size = 13.5 × 15.5 µm; Q = 1.14), thin-walled, hyaline, some with a germinative tube. The spores form small globose ameroconidia, 10 × 10 µm, thin-walled, hyaline.

Ecology and distribution:— Saccosoma megasporum grows on fallen branches of Abies religiosa . The species is known only from the type locality in central Mexico.

Comments:— Saccosoma megasporum can be differentiated based on the size and shape of its basidiospores which are larger (12–15 × 15–17 µm) than other subglobose-spored species in the genus. The close S. farinaceum has ellipsoid basidiospores ( Q = 1.44) and larger basidia ( Table 2).

Figures

FIGURE 2. Saccosoma megasporum (holotype, MEXU: 28247). A. Hypochnoid basidiome; B–C. basidiospore with germinative tube and conidia; D–E. probasidia; F–G. hyphae with clamp connections; H–I. 4-cell tubular basidia.