Cystolepiota rhodella Sysoup. and Thongkl.
Pileus 10–32 mm diam., first conical to paraboloid, expanding to campanulate or convex, often umbonate with broad umbo, with straight to incurved margin, completely covered by flocculose squamules when young, violet-brown (10E4–8 and 11E6–8) to greyish ruby or ruby (12C5–8, 12D5–8, and 12E5–8), darker at center, on drying becoming darker, greyish brown to dark brown (8F3–4), on white to pinkish-white or pale red (8A2–3) background; margin with flocculose squamules, concolorous with those on surface, often with white to orange grey (5B2) cortina connecting with stipe when young. Lamellae free, white to whitish, 2–4 mm wide, broadly ventricose, with wavy eroded edge, concolorous with squamules on pileus and stipe, with three lamellulae. Stipe 25–40 × 2–5 mm, cylindrical, covered with crowded flocculose squamules, concolorous with those on pileus, on white to pinkish white or pale red (8A2–3) background, with white rhizomorphs at base; hollow. Annulus an annular zone with concolorous flocculose squamules at upper part of stipe, with concolorous cortina as on pileus margin. Context white in pileus and up to 2 mm thick at umbo, white in stipe. Odor and smell not observed. Spore print white to whitish.
Basidiospores (50,2,2) 3.8–4.2 × 2–3 µm, avl × avw = 4 × 2.4 µm, Q = 1.4–1.9, avQ = 1.7, oblong-ovoid in side view, some with straight base, and with rounded or slightly acute apex, ellipsoid to oblong in frontal view, hyaline, thick-walled, dextrinoid, non-amyloid. Basidia 13–15 × 4.5–6 µm, clavate, hyaline, slightly thick-walled, four-spored. Lamella edge sterile, with abundant cheilocystidia. Cheilocystidia 35–40 × 4–7 µm, moniliform to flexuous with long appendiculate apex, some narrowly lageniform, with pale yellow mucilaginous contents, hyaline and slightly thick-walled. Pleurocystidia absent. Pileus covering an irregular epithelium composed of globose (12–65 µm diam.) to subglobose (17–23 × 12–18 µm) elements in upper layers, with oblong (25–38 × 15–20 µm) elements in lower layers, thin-walled, with pale brown parietal and intracellular pigments. Stipe covering in the squamules an irregular epithelium same as in pileus covering. Clamp connections present.
Habitat and habit: growing solitary or in a small group, saprotrophic on humus-rich soil with dead leaves, in various habitats, e.g., mixed deciduous forest with Castanopsis spp. and Lithocarpus spp. as dominant tree species in northern Laos, in dipterocarp forest with Shorea obtusa Wall. ex Blume dominant, and in deciduous forest of Ficus annulata Blume in northern Thailand.
Materials examined: Thailand, Chiang Rai Province, Pa Daed District, Pha Ngae Sub-district, 19°34′57″ N, 100°00′51″ E, alt. 510–540 m, 28 August 2018, P. Sysouphanthong, PS2018-138 (MFLU22-0019); Chiang Mai, Mae Taeng District, Pong Duad Village, 16°06′16.1″ N, 99°43′07.9″ E, alt. 780–805 m, 9 August 2007, P. Sysouphanthong, PNG31 (MFLU09-0050).
Note: Cystolepiota rhodella was found in dipterocarp forests (and other habitats) in Northern Laos and Northern Thailand. It is easily recognized by violet-brown or greyish-ruby to ruby squamules on basidiomata and white lamellae with violet-brown edges. Because of its unique color and the colored lamella edge, the species stands out, and there are few similar species. Melanophyllum haematospermum (Bull.) Kreisel differs from C. rhodella by cinnamon or pale brownish-gray to light grayish-brown basidiomata and cinnamon-red to dark brown lamellae. Microscopically it differs in the subtly ornamented colored spores and cystidia that are in general absent or, if present, inconspicuous; the exsiccata turn black. The phylogram showed that C. rhodella is separated from other species; it is basal to the clade made up of specimens of C. hetieri (Boud.) Singer.
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.