Tricholoma viscidum L. Fan, N. Mao & J. J Yang 2025, sp. nov.

Tricholoma viscidum L. Fan, N. Mao & J. J Yang sp. nov. Figs 2 G, H, 3 F, H Diagnosis. It is distinguished by the combination of the following features: pileus surface viscid when wet, stipe surface covered with brown to dark brown fibrils, and broadly ellipsoid basidiospores. It is most similar to T. ustaloides Romagn. but differs in the absence of a sharply defined zone of white color on the upper part of the stipe surface. Holotype. China • Shanxi Province, Qinshui County, Lishan Mountain, 35°29'8"N, 113°1'19"E, elev. 1658 m, on the ground in broadleaf forest dominated by Quercus sp., 29 September 2023, J. Z. Cao, MS 843 (BJTC FM 4198), GenBank Acc. No.: ITS = PQ 499539, mtSSU = PQ 499571, tef 1 - α = PQ 509903, rpb 2 = PQ 509913, mcm 7 = PQ 509924. Etymology. viscidum (Lat.): referring to the viscid cap of basidiomata when wet. Description. Basidiomata small, medium to large-sized. Pileus 33–86 mm diam., at first hemispherical to convex, later plano-convex with age, with an umbo at center; surface viscid when wet, yellowish brown (# e 6 d 3 b 8), brown (# d 0 b 79 d) to reddish brown (# 9 d 6463), darker in the center and paler towards the margin, covered with brown (# ab 7 d 6 b) fibrils; margin at first involute, later incurved, cracking with age. Lamellae sinuate, crowded, dirty white (# f 3 fbd 0) to pale yellow (# f 1 ffb 8), turning brown (# c 09 a 7 e) with age; lamellulae in 2–3 tiers, concolorous with lamellae. Stipe 49–113 mm long, 10–18 mm diam., cylindrical to clavate, enlarged downwards, dry, yellowish brown (# c 79 f 5 c) to brown (# 9 f 6327), covered with brown (# b 99976) to dark brown (# 8 b 6 c 68) fibrils. Context white (# f 3 eeea), up to 13 mm. Odor unrecorded. Taste not recorded. Basidiospores [120 / 3 / 4] 5–6.5 × 4.5–5.5 μm, Q = 1.1–1.25, broadly ellipsoid to ellipsoid, smooth, inamyloid, usually containing one large oil droplet. Basidia 28–37 × 5–8 μm, clavate, (2 –) 4 - spored, sterigmata up to 5.5 μm long. Cystidioid cells in hymenium absent. Hymenophoral trama regular, composed of cylindrical hyphae, 5–10.5 μm wide, colorless in water and 5 % KOH. Pileipellis a cutis, composed of cylindrical hyphae, 4–9.5 µm wide, yellowish-brown in water and 5 % KOH. Stipitipellis a cutis, composed of parallel hyphae, 2.5–6 µm wide, colorless in water and 5 % KOH. Clamps absent in tissues. Ecology and habitat. Scattered or gregarious on the ground in broadleaf forest dominated by Quercus sp., currently only known from Shanxi Province, northern China. Additional specimens examined. China • Shanxi Province, Qinshui County, Lishan Mountain, on the ground in broadleaf forest dominated by Quercus sp., 5 October 2023, J. Z. Cao, CF 2268 (BJTC FM 4038), GenBank Acc. No.: ITS = PQ 499541; ibid., 29 September 2023, J. Z. Cao, MS 844 (BJTC FM 4199), GenBank Acc. No.: ITS = PQ 499542, mtSSU = PQ 499572, tef 1 - α = PQ 509904, rpb 2 = PQ 509914, mcm 7 = PQ 509925; ibid., 25 August 2023, H. M. Ji MS 443 (BJTC FM 3388), GenBank Acc. No.: ITS = PQ 499540, mtSSU = PQ 499570, tef 1 - α = PQ 509902, rpb 2 = PQ 509912, mcm 7 = PQ 509923. Notes. Tricholoma viscidum belongs to the sect. Genuina (Fig. 1). Tricholoma ustaloides is closely related to the new species in morphology and phylogeny. They all have ellipsoid basidiospores and are associated with the Quercus spp. However, T. ustaloides differs from T. viscidum by its upper part of the stipe decorated with a distinctly and sharply delimited zone (Christensen and Heilmann-Clausen 2013; Halama et al. 2016). Tricholoma ustale (Fr.) P. Kumm., a European species often associated with Fagus spp. and Carpinus spp., is also easily confused with the new species as there are some reports that it is related to Quercus forests. However, T. ustale differs by its stipe flesh turning reddish brown when cut or bruised and its phylogenetic position (Christensen and Heilmann-Clausen 2013).