Tuber mongolicum T. Bau & F. Guo sp.nov. (Figure 2–5)

MycoBank number:—846829

Diagnosis:— Tuber mongolicum differs from related species by its pseudoparenchymatous peridum, ellipsoid ascospores and 1–5 spored asci.

Etymology:—‘mongolicum’ refers to its occurrence in Inner Mongolia Autonomous Region, China.

Types:— CHINA, Inner Mongolia Autonomous Region, Tongliao Daqinggou National Nature Reserve, in soil under Populus sp., 42°47′N, 122°10′E, 214 m, 23 Aug. 2022, Fang Guo, Tolgor Bau, HMJAU65125 (holotypus!). Same location; Fang Guo, Tolgor Bau HMJAU65126 (paratypus!) .

Description:—Ascomata are spherical to irregular spherical, 0.8–1.5 cm in diameter, with depressions. The surface is yellowish-green (30B7), olive-brown (4D7) to yellowish brown (5D8) when fresh, with small protrusions at the concave part of the fruiting body. Gleba is yellow-brown with white veins that have a sparse radial distribution from the base, and starch-like aroma (Figs 2–3).

Peridum is 349–506 µm, thick, with two layers: the outer layer is yellow-brown, and 71–174 μm thick, the inner layer is a clear shade, 205–418 μm thick, and composed of sub-globose pseudoparenchymatous cells of 15–33 × 9–20 µm wide (Figs 4a, 5c). Asci are usually 1–4-spored, but occasionally 5-spored. Asci are sub-globose to ellipsoid, thin-walled, and short or nearly sessile, measuring 56–91 × 46–68 µm (Figs. 4 b-c. 5b). Ascospores are oblong-ellipsoid, ellipsoid to broadly ellipsoid, yellow-brown at maturity, and reticulate. In 1-spored asci 38–50 × 30–40 µm, Q=1.1–1.28, in 2- spored asci 33–44 × 25–37 µm, Q=1.1–1.4, in 3-spored asci 28–40 × 22–28 µm, Q=1.15–1.43, in 4-spored asci 25–35 × 20–29 µm, Q=1.15–1.37, in 5-spored asci 26–31 × 22–25 µm, Q=1.1–1.24, spike ornamentation 2.92–5.06 µm length, and mostly 3–6 meshes across the spore width (Figs 4 b-c, 5b).

Habitat: Hypogeous, in soil under Populus sp.; ascoma occurring in autumn.

Distribution: Only within Inner Mongolia Autonomous Region, Northern China.