Tuber conditum T. J. Yuan, S. H. Li & X. H. Wang 2025, sp. nov.

Tuber conditum T. J. Yuan, S. H. Li & X. H. Wang sp. nov. Fig. 4 a – f Typification. China • Yunnan Province: Changning County (38.3903°N, 102.3535°E), in soil under mixed forest, with Pinus yunnanensis dominant, 20 Sep 2020, S. H. Li L 3385 (holotype YAAS L 3385, paratype YAAS L 3682). Gene sequences ex holotype. ON 454665 (ITS); ON 428901 (LSU); ex paratype: ON 454667 (ITS). Etymology. Conditum, Latin, refers to the acrid smell of ascocarp. Diagnosis. Tuber conditum differs from other species by having no cystidia on surface of ascomata, thinner peridium, and larger ellipsoid ascospores. Description. Ascomata (Fig. 4 a) 3–4 cm diam., subglobose, hypogeous, grey-white to grey-brown (4 A 2-4; 4 B 3-4), surface smooth, with a few pinholes; acrid smell, taste not recorded. Peridium (Fig. 4 b) one-layered, 120–200 µm thick, prosenchymatous, composed of interwoven hyphae 1.5–2.5 µm broad with thin-walled, and lumens 1.5–2.5 (3.5) µm diam, with ellipsoid or irregular cells of 15 × 10 μm diam. Sometimes intermixed, wall thickness 1–2 μm. Gleba (Fig. 4 a, c) solid, firm, brown to black (6 E 7-8; (5-9) F 8) at maturity, marbled with whitish narrow veins. Asci (Fig. 4 d – e) subglobose or irregular, 1–4 spored, hyaline, thin-walled or occasionally with walls as thick as 2 μm, sessile stalk, 55–100 × 45–75 μm (n = 30). Ascospores (Fig. 4 d – f) subglobose or ellipsoid, pale yellow (2 A 2-4), yellow-brown (5 D 6-8; 5 E 7-8) at maturity, excluding ornamentation, 49–66.5 × 34.5–60 μm, Q = 1.02–1.58 (n = 54), in one-spored asci, 33–54.5 × 30–47 μm, Q = 1.06–1.35 (n = 50), in two-spored asci, 21.5–44 × 21–37 μm, Q = 1.00–1.26 (n = 60), in three-spored asci, 20.5–40.0 × 20–35.5 μm, Q = 1.01–1.30 (n = 40), in four-spored asci, Q = 1.15 ± 0.23, reticulate ornamentation 2–5 μm in height, composed of irregular hexagonal meshes, 6–8 along the spore length and 3–6 along the breadth. Distribution and habitat. China: Yunnan province, Changning county, hypogeous, in the soil in woods dominated by Pinus yunnanensis. Notes. Tuber conditum is phylogenetically closely related to Tuber tomentosum (Kinoshita et al. 2011), T. qujingense, and T. songlu (Wan et al. 2021). However, T. conditum has no cystidia on the surface of ascomata and larger ellipsoid ascospores, differing from T. tomentosum (Kinoshita et al. 2011; Sasaki et al. 2016). Tuber conditum differs from T. qujingense and T. songlu by its thinner peridium (120–200 µm) and larger ascospores (49–66.5 × 34.5–60 μm in one-spored asci). Tuber qujingense has a greyish-white ascomata, brown snowflake-shaped gleba, and prosenchymatous peridium, fusiform, and T. songlu has dense spine-like dermatocystidia, which are completely different from each other. In addition, DNA sequence analysis revealed the similarity between two species is less than 82.73 % (T. qujingense) and 93 % (T. songlu) in ITS sequences, strongly supporting the separation of T. conditum from the Chinese species of T. qujingense and T. songlu. Phylogenetic analysis (Figs 1, 2) also suggested that T. conditum is a distinct species because all sequences of this new species clustered within a strong bootstrap (BS ≥ 99 % and PP = 1.0). The truffle has the acrid smell, which might be a good identifying feature for the fungus.