Cystolepiota thailandica Yuan S. Liu, Sysouph. and Thongkl
Pileus 25–32 mm diam., first hemispherical to convex, expanding to convex or slightly plano-concave, with inflexed margin, when young granulose to powdery, greyish orange (6B3–5), soon breaking up, granulose to powdery at center toward margin, sometimes fragile when mature, on white powdery background; margin covered with granulose to powdery velar remnants, concolorous to those on surface. Lamellae free, 1.5–2 mm wide, crowded, white, broadly ventricose, with 3–4 lamellulae, with concolorous eroded edge, turning light brown to brown (7D5–8) when touched. Stipe 25–35 × 1.5–2.5 mm, cylindrical, completely covered with white to greyish orange (6B3–5) granulose to powdery velar remnants, on white background, turning light brown to brown (7D5-8) when touched. Annulus an annular zone with white to greyish-orange (6B3–5) remnants. Context white in pileus, 1–1.5 mm thick at center; hollow in stipe and concolorous with surface. Odor and taste not observed. Spore print white.
Basidiospores (50,2,2) 4.0–5.0 × 1.8–2.5 µm, avl × avw = 4.30 × 2.24 µm, Q = 1.7–2.0, avQ = 1.91, ellipsoid in frontal view, ellipsoid in side-view, slightly thick-walled, smooth, hyaline, non-dextrinoid, non-amyloid. Basidia 15–20 × 5.0–7.0 µm, short clavate to clavate, thin-walled, hyaline, four-spored. Cheilocystidia absent. Pleurocystidia absent. Pileus covering an epithelium composed of globose to subglobose and sphaeropedunculate element cells, 10–35 µm wide, hyaline to pale brown parietal pigments. Stipe covering an epithelium similar to that on pileus. Clamp connections present in all tissues.
Habitat and habit: growing solitary or in a small group with few basidiomata, saprotrophic on humus-rich soil with dead leaves. Found under cultivated trees of Ficus annulata Blume.
Additional materials examined: Thailand, Chiang Rai Province, Muang District, Mae Fah Luang University Campus, 11 January 2019, Yuan S. Liu, STO-2019-063 (MFLU22-0018).
Notes: Cystolepiota thailandica is not related to any species in the genus by morphology. Cystolepiota seminuda (Lasch) Bon is similar to C. thailandica by having globose and sphaeropedunculate element cells on pileus and stipe covering and an absence of cheilo- and pleurocystidia but is different in having a white to pale pink or yellowish pileus and stipe covering and slightly larger basidiospores (3.5–5.5 × 2.0–3.0 µm). Cystolepiota bucknallii (Berk. and Broome) Singer & Clémençon is different by having a lilac or violaceous powdery covering on the pileus and stipe, pale yellow to pastel yellow lamellae, and lacking sphaeropedunculate element cells. Cystolepiota pseudogranulosa (Berk. & Broome) Pegler, described from Sri Lanka, differs in the strongly dextrinoid spores and the irregularly shaped pileus covering elements. The phylogram shows that C. thailandica is separated from the other species for which sequence data are available.
Fig. 1 Maximum-likelihood phylogram of Cystolepiota and Melanophyllum specimens based on combined nrITS-LSU and RPB2 sequences. New sequences generated for this study are in blue. Bootstrap values of ML ≥ 60%, and BI ≥ 0.95 are indicated above the branches (ML/BI). Agaricus campestris L. and Agaricus friesianus L.A. Parra, Olariaga & Callac are chosen as outgroup.