Marasmius variicystidiatus T. Bau & W. N. Hou 2026, sp. nov.

Marasmius variicystidiatus T. Bau & W. N. Hou sp. nov. Figs 5 D, 5 E, 9 Diagnosis. It is similar to Ma. oreades, but differs in having a thin, cream-colored context and a faintly sweet odor. Etymology. “ variicystidiatus ” refers to pileipellis cells with irregular terminal branches. Description. Basidiomata small to medium-sized. Pileus 0.6–3 cm diam., initially plano-convex, becoming nearly plane with age, with a shallow central depression; surface white (RAL 9003), smooth, pale brown (RAL 8025) at center; margin slightly reflexed, membranous, shallowly grooved, becoming water-soaked, translucent, and distinctly striate when moist. Context cream (RAL 9001), thin; odor faintly sweet. Lamellae sinuate to adnate, sparse, moderately broad, 2–3 mm wide, L = 20–23, I = 10–15, cream (RAL 9001); edges smooth and entire. Stipe 3.6–6 cm long, 1–2 mm thick, subcylindrical, equal or tapering downwards, hollow, fibrous; apex cream (RAL 9001) to milky white with a greyish tint (RAL 7044), middle clay brown (RAL 8001) to warm brown (RAL 8003), base beige-brown (RAL 8024) to reddish brown (RAL 8012); surface covered with a cream-colored (RAL 9001), pruinose mycelial layer; base attached to habitat with white (RAL 9003) mycelium. Basidiospores (6.7) 6.9–10.6 (10.9) × (2.5) 3.5–4.7 (4.7) µm, Q = (1.79) 1.82–2.54 (2.86) [2.15 ± 0.26], lacrymoid, smooth, thin-walled, hyaline, inamyloid. Basidia 23–30 × 3.5–6.1 µm, elongate-clavate, smooth, thin-walled, hyaline, 4 - sterigmate, rarely 2 - sterigmate, with a basal clamp connection. Cheilocystidia absent. Pleurocystidia absent. Lamellar trama irregular; hyphae weakly dextrinoid, with clamp connections. Pileipellis hymeniform, composed of Globulares - type cells, 4.8–23 × 2.5–9.2 µm, subglobose to ellipsoid, with irregular terminal branches, thin- to slightly thick-walled, inamyloid. Pileus trama composed of interwoven, cylindrical, dextrinoid hyphae 5.7–10.4 µm wide, with clamp connections. Stipitipellis hyphae 3.1–5 µm wide, elongate-cylindrical, pale yellow; subpellis hyphae parallel, 4–5.5 µm wide, cylindrical, yellowish brown to dark yellowish brown. Stipe trama hyphae parallel, 4.3–5 µm wide, cylindrical, hyaline. Caulocystidia absent. Clamp connections present in all tissues. Typus. CHINA • Inner Mongolia Autonomous Region, Tongliao City, Horqin Left Wing Middle Banner, Wusitu National Nature Reserve, on litter in broad-leaved forests, 10 July 2022, 43°47'47"N, 123°17'40"E, alt. 145 m, T. Bau & L. S. Mu, FJAU 69373 (m 05), holotype!. Additional materials examined. CHINA • Inner Mongolia Autonomous Region, Tongliao City, Horqin Left Wing Rear Banner, Yihuta, on decaying leaves of broad-leaved trees, 14 July 2022, 43°13'21"N, 122°24'58"E, alt. 222 m, Tolgor & W. N. Hou, FJAU 69371 (H 220787). • Tongliao City, Horqin Left Wing Rear Banner, Wudantala Forest Farm, on decaying leaves of broad-leaved trees, 16 July 2022, 42°59'55"N, 122°46'08"E, alt. 205 m, Tolgor & W. N. Hou, FJAU 69443 (H 2207154). Notes. It belongs to Marasmius subg. Globulares sect. Globulares subsect. Globulares ser. Wynnearum. Ma. torquescens Quél. and Ma. wynneae Berk. & Broome are also similar to Ma. variicystidiatus, sharing a shallowly grooved pileus margin and comparable stipe coloration. Ma. torquescens differs by bearing a blunt fulvous umbo at the pileus center (Quélet 1872). Ma. wynneae can be distinguished by its grayish-white pileus with a purplish tint and lamellae that also exhibit a purplish tint (Antonín et al. 2014 a; Berkeley and Broome 1859). Ma. variicystidiatus forms a distinct clade with strong support and shows a close relationship to Ma. albogriseus (Peck) Singer. The two species are largely similar in pileus shape, color, and marginal striations. However, Ma. albogriseus differs from the present species by having more distant lamellae, with whitish lamellae tinged orange-gray and conspicuous intervenose veins, and clavate pileipellis cells (Deng 2012). The stipe of Ma. albogriseus is paler in color, and its basidia are slightly shorter and broader relative to those of this species. In addition, Ma. albogriseus possesses polymorphic cheilocystidia, which may be cylindrical, subbasidioid, or irregularly inflated at one end, whereas such structures are not observed in the present species. Comparisons with its original description indicate that Ma. wynneae has a pale lilac-brown pileus and a hollow, nearly concolorous stipe, features that readily distinguish it from Ma. variicystidiatus (Berkeley and Broome 1859). The pileus and stipe colors reported for Ma. wynneae by Læssøe and Petersen (2019) differ from those given in the original description. The pileus has a grayish-white tone. In general, early collections and descriptions of Ma. oreades were primarily concentrated in Europe and North America. Later, the distribution of this species was reported from many regions across the globe. Nevertheless, numerous researchers have found that the true taxonomic status of specimens identified as “ Ma. oreades ” is questionable. A large number of sequences deposited in the NCBI database under the name “ Ma. oreades ” are scattered across different phylogenetic lineages within Marasmius, creating substantial confusion for taxonomic studies of this genus. According to the most recent taxonomic revision, the true “ Ma. oreades ” should be circumscribed within Marasmius subg. Globulares sect. Globulares subsect. Globulares (Thorén et al. 2025). According to Oliveira et al. (2024 a), Ma. oreades specimens (e. g., BUNS 12-00735) from Europe (e. g., Denmark and Switzerland) and North America (e. g., the United States and Canada) may represent the core clade of true Ma. oreades, which may correspond to the typical evolutionary clade of this species in Europe and North America. The species under discussion is easily confused with Ma. oreades. However, Ma. oreades differs in having a thick, pale-yellow context, a stipe that is white in the upper part and pale brown at the base, short clavate pileipellis cells, and an odor reminiscent of bitter almonds. Macroscopically, Ma. variicystidiatus can also be easily confused with Ma. bellus Berk. In contrast, Ma. bellus can be effectively distinguished by its pileipellis, which contains abundant Siccus - type cells (Oliveira et al. 2020 b).