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

Marasmius clavocystidiatus T. Bau & W. N. Hou sp. nov. Figs 4 J – L, 12 Diagnosis. It is characterized by a white pileus with tea-brown to deep reddish-brown protrusions and radial grooves, translucent from the rim of the central depression to the pileus margin when moist, cheilocystidia Rotalis - type, clavate, pileipellis cells Siccus - and Rotalis - type, cylindrical to clavate. Etymology. “ clavocystidiatus ” refers to clavate cheilocystidia. Description. Basidiomata small. Pileus 4–7 mm diam., initially campanulate, becoming convex at maturity, apex truncate and centrally depressed, bearing a prominent, pointed papilla within the depression, surface white (RAL 1013), radially grooved, translucent from the rim of the central depression to the pileus margin when moist, papilla tea-brown (RAL 8003) to deep reddish-brown (RAL 8004), margin wavy. Context creamy white (RAL 9001), thin; odor indistinct. Lamellae free, with a collar-like structure, sparse, equal, L = 10–12, dirty white. Stipe 0.8–1.7 cm long, 0.5 mm thick, filiform; entirely translucent when young; apex white (RAL 9001) or nearly translucent at maturity and moist, middle pale brown (RAL 3011) to blackish-brown (RAL 3004), base black (RAL 9004); surface smooth; base directly attached to habitat. Basidiospores (6.5) 6.6–8.9 (8.9) × (3) 3.1–4.4 (4.5) µm, Q = (1.69) 1.88–2.44 (2.47) [2.13 ± 0.19], lacrymoid, smooth, hyaline, inamyloid. Basidia 17–23 × 4.3–5.9 µm, clavate, inamyloid, 4 - (rarely 2 -) sterigmate; sterigmata 2.3–3.1 µm long. Basidioles of two types: narrowly clavate, 14–22 × 2.6–4.9 µm, and narrowly fusiform, 22–28 × 3.4–4.8 µm, slightly protruding beyond the hymenium, smooth, thin-walled. Cheilocystidia Rotalis - type, main body 11–20 × 2.8–13 µm, clavate; surface bearing 10–25 projections concentrated at the apex; projections 2.1–4 µm high. Pleurocystidia absent. Lamellar trama irregular; hyphae 3.2–4.2 µm wide, inamyloid. Pileipellis hymeniform, composed of Siccus - and Rotalis - type cells, main body 8.4–20 × 8–13 µm, cylindrical to clavate, sometimes with a short basal stalk; projections 2–4.4 µm high, dark brown in 5 % KOH, extremely dense to confluent, concentrated at the cystidial apex. Pileus trama composed of irregular, thin-walled, weakly dextrinoid hyphae 2.6–4.2 µm wide. Stipitipellis composed of regular, thick-walled hyphae 3.7–5.5 µm wide, dark brown in 5 % KOH. Typus. CHINA • Heilongjiang Province, Greater Khingan Mountains Region, Jiagedaqi District, roadside on both sides of National Highway G 111, on piles of dead grass in meadows, 28 July 2024, 50°19'05"N, 124°14'20"E, alt. 470 m, H. B. Song, FJAU 69402 (S 24072803), holotype!. Additional materials examined. CHINA • Heilongjiang Province, Greater Khingan Mountains Region, Jiagedaqi District, roadside on both sides of National Highway G 111, on piles of dead grass in meadow, 28 July 2024, 50°19'10"N, 124°14'18"E, alt. 470 m, H. Cheng, FJAU 69401 (C 2472801). • Jilin Province, Changchun City, the campus of Jilin Agricultural University, 17 July 2024, 43°48'26"N, 125°25'12"E, alt. 229 m, T. Bau & H. Y. Bao, FJAU 69403 (H 247206). • Jilin Province, Changchun City, the campus of Jilin Agricultural University, on decaying leaf litter of broad-leaved trees, 16 June 2026, 43°48'48"N, 125°24'58"E, alt. 395 m, W. N. Hou, FJAU 69455 (H 26060013). • Jilin Province, Changchun City, the campus of Jilin Agricultural University, on decaying walnut fruits, 18 June 2026, 43°48'27"N, 125°25'00"E, alt. 234 m, X. Y. Zhou, FJAU 69456 (Y 2661810). Notes. It resembles Ma. leucorotalis, as both display a pileus with an umbilicate depression and a slightly elevated central papilla. However, the type specimen of Ma. leucorotalis (B 1414 LIL) is distinguished by a small black spot within the central umbilicate depression of the pileus, basidiospores measuring 7–7.8 × 2.7–3 μm, dextrinoid lamellar trama, and globose to subcystidioid Rotalis - type cheilocystidia and pileipellis cells (Singer 1965). Tan et al. (2009) described a Malaysian specimen identified as Ma. leucorotalis (TYS 486, SFSU), but this material deviates from the original description, most prominently in having inamyloid lamellar trama; thus, its identification requires further verification. In contrast, Brazilian specimens identified as Ma. leucorotalis largely conform to Singer’s (1976) description, with only minor differences in basidiospore size. Consistent with the examined specimens, the Malaysian specimen TYS 486 (SFSU) also exhibits inamyloid lamellar trama. It differs, however, in the morphology of both cheilocystidia and pileipellis cells. Furthermore, the available sequences of the Malaysian specimen are of poor quality, preventing reliable comparisons with the sequences generated from the specimens examined in this study. Sequences from Brazilian Ma. leucorotalis specimens were included in the analyses. These specimens feature a white to grayish-white depressed area at the pileus center when fresh, while the region outside the depression is grayish brown to pale gray-brown, darkening and ultimately turning brown upon drying. They also have dextrinoid lamellar trama, with pyriform, vesiculose, subglobose to globose cheilocystidia and pileipellis cells. In comparison, Ma. clavocystidiatus presents a white pileus surface with a tea-brown to deep reddish-brown papilla, inamyloid lamellar trama, Rotalis - type clavate cheilocystidia, and cylindrical to clavate Siccus - and Rotalis - type pileipellis cells. These morphological differences clearly separate this new species from Ma. leucorotalis (Oliveira et al. 2020 b). In addition, the difference between Ma. clavocystidiatus and Ma. rotalis Berk. & Broome should be considered. Ma. rotalis is an early-described species with relatively limited morphological information in its protologue, and numerous distinct taxa have historically been assigned to this name. Comparison with the original description indicates that Ma. clavocystidiatus differs from Ma. rotalis primarily in pileus surface characteristics: Ma. rotalis has a pileus covered with dark brown pruina, whereas Ma. clavocystidiatus has a white pileus surface bearing a tea-brown to deep reddish-brown papilla (Berkeley and Broome 1873). In the phylogenetic tree, specimens FJAU 69402, FJAU 69401, and FJAU 69403 clustered together within a distinct major clade with strong support (BS = 99 %, UFBoot = 1). A certain degree of genetic distance was still observed between FJAU 69402 and the other two specimens, FJAU 69401 and FJAU 69403. Sequence alignment suggested that the variation observed in FJAU 69402 may be attributable to intraspecific polymorphism, a phenomenon that appears relatively common in fungi (Cedeño-Sanchez et al. 2024). Because the basidiomata of FJAU 69403 were already dry at the time of collection, some key morphological characters may have been lost. For this reason, FJAU 69403 was not designated as the type specimen; instead, the better-preserved specimen FJAU 69402 was selected as the holotype of Ma. clavocystidiatus.