Pluteus losulus Justo, Myco. Progr.
Index fungorum number 518507
Pileus 52–95 mm diam., broadly convex-umbonate to plano-convex with a shallow broad umbo; margin decurved, split in age; surface dull, dry, radially streaked, appressed-fibrillose, greyish brown (7E3) with a dark greyish brown (7F4) disc and streaks. Context 2–4 mm thick, soft, white. Lamellae free, close to crowded with 3 series of lamellulae, broad (up to 7 mm), initially white and becoming greyish red (7B3). Stipe 70–80 _ 6–9 mm, central, cylindrical above an enlarged base, solid, pliant; surface dull, dry, glabrous above, base appressed-fibrillose, white overall when young, in age base becoming greyish brown (7E3). Basidiospores 6–7(–8) × (5.5)6–6.5 µm (x = 6.74 ± 0.51 × 6.12 ± 0.25, Q = 1.00–1.23,q = 1.10 ± 0.06, s = 1) globose to subglobose, smooth, hyaline, inamyloid, thick-walled. Basidia 25–30 × 9–10 µm, clavate, thin-walled, 4-spored. Lamellar edge sterile. Cheilocystidia common, 19–55 × 9–16 µm, clavate to subclavate, hyaline, inamyloid. Pleurocystidia common, 54–65 × 11–22 µm, ventricose to utriform, with 3–4 apical hooks, straight to recurved hook, hyaline, inamyloid, thick-walled (up t2 µm). Pileipellis a cutis of repent hyphae, with terminal element 37–90 × 6–11 µm, cylindrical, acute or round toward the apex, with brown cytoplasmic pigment, thin-walled. Pileus trama regular, hyphae (3–)5–17 µm diam., cylindrical, hyaline, inamyloid, non-gelatinous, thin-walled. Lamellar trama convergent, hyphae (2–)4–11 µm diam., cylindrical, hyaline, inamyloid, non-gelatinous, thin-walled. Stipitipellis a cutis with caulocystidia, hyphae 5–13 _m diam., cylindrical, hyaline or with brown cytoplasmic pigment, inamylid, non-incrustrated, non-gelatinous, thin-walled. Caulocystidia scattered, 42–73 × 10–11 µm, cylindrical, fusiform, acute or round toward the apex, with brown cytoplasmic pigment, thin-walled. Clamp connections present in all tissues.
Habit, habitat, and known distribution: Solitary or gregarious on rotting wood in bamboo thickets, deciduous dipterocarp-oak forests, secondary forest and coffee plantations in DR Congo, Principe Island, and Thailand.
Specimen examined: THAILAND, Chiang Mai Province, Chiang Mai University campus, on rotting wood, August 2020, N. Suwannarach & J. Kumla, SDBR-CMUNK0842.
Notes: Pluteus losulus is recognized by relatively large basidiomata that are planoconvex with a broad umbo pileus, fully covered with dark greyish brown appressed fibrillose, white to greyish brown stipe, globose to subglobose basidiospores with mean dimensions of 6.7 × 6.1 µm, simple clavate, thin-walled cheilocystidia, apical hooked pleurocystidia, a cutis pileipellis with cylindrical to fusiform terminal cells, and the presence of a clamp connection. Accordingly, these features would indicate placement in sect. Pluteus.
Our Thai material matches nicely with the African material that had designated this species as P. losulus by Justo, while also sharing a resemblance with the recently reported São Tomé material. The ITS sequences of the Thai material were identical to those of African (GF 5273), São Tomé (SFSU:DED 8313), and Chinese (GDGM47122) materials with 100%, 100%, and 99.85%, respectively. Moreover, the nrLSU sequence of Thai material is similar to African material (GF 5273) with 100%. According to the ITS phylogram of the Pluteus sect. Pluteus a sequence of the Thai material was determined to be clad with the sequences of P. losulus with strong statistical support (100% bootstrap support and 1.0 Bayesian posterior probabilities).