Agaricus flammicolor Linda J. Chen, Callac, R.L. Zhao & K.D. Hyde
Index Fungorum number 818050, Facesoffungi number: FoF 02286.
Pileus 4–7 cm diam, 2–4 mm thick at disc, at first parabolic, sometimes truncated at disc, then becoming hemispherical to convex, finally applanate; surface dry, with bright orange fibrils, densely at disc and radially arranged elsewhere, sometimes with fibrils bunching together into finely squamules, on a white background; strongly flavescent when bruised. Margin incurved, shortly exceeding the lamellae, often with appendiculate remains of the annulus. Lamellae free, crowded, 3–4 mm broad, with intercalated lamellulae, first white, then pinkish brown, finally dark brown. Stipe 50–87 × 4–6 mm (8–12 mm at base), clavate or cylindrical with slightly bulbous base, fistulose, surface above the ring smooth, below the ring heavily fibrillose, white, strongly flavescent when rubbed. Annulus simple, superous, membranous, upper surface smooth, lower surface fibrillose, white, except sometimes with orange tinge close to the margin at the lower surface. Odour of almonds. Context firm, white, slightly yellowish at stipe when cut.
Spores 4.4–5.3(–6.2) × 2.5–3.2 µm, (x = 4.9 ± 0.25 × 2.9 ± 0.15 µm, Q = 1.53–1.91, Qm = 1.69 ± 0.04, n = 20), ellipsoid to oblong, smooth, brown, thick-walled. Basidia 12–16 × 5–6 µm, broadly clavate, hyaline, smooth, 4-spored. Cheilocystidia 21–45 × 10–25 µm, abundant, simple, pyriform, broadly clavate or sphaeropedunculate, rarely rostrate or mucronated, with yellowish pigment, smooth. Pleurocystidia absent. Pileipellis a cutis composed of hyphae of 5–7 µm diam, cylindrical, hyaline, smooth, not constricted at the septa. Macrochemical reactions — KOH reaction positive, bright yellow. Schäffer’s reaction positive, bright orange.
Etymology: The epithet ‘flammicolor’ refers to the orange colour like a flame.
Habitat: Solitary or scattered, on soil, under an Albizia tree.
Material examined: CHINA, Yunnan Prov., Cangyuan county, 11 July 2012, P. Callac & J. Guinberteau, ZRL2012270 (HMAS279148). – Thailand, Chiang Rai Prov., Mae Fah Luang University, 28 July 2015, J. Chen, LD201502 (holotype MFLU16-0982); Chiang Mai Prov., Thang Thong village, 31 June 2012, J. Chen, LD201225 (MFLU12-0869).
Notes: Agaricus flammicolor is well characterized by a pileus surface covered with bright orange fibrils or fine squamules, spores on average less than 3 μm in width, and with simple and large cheilocystidia containing yellowish pigments. Among the known taxa of A. sect. Minores, species with a pileus surface showing orange tinges are very rare. Agaricus entibigae, originally described from Hawaii, also has a pale orange to brownish orange pileus, but it differs in having its stipe surface base covered with reddish squamules, wider spores (3.8 μm on average) and smaller cheilocystidia. According to the phylogenetic results. A. flammicolor is closely related to A. badioniveus/LD2012131, another new species treated in this study.
Fig. 1 Maximum Clade Credibility tree of Agaricus resulting from analysis of ITS, LSU, tef-1α sequence data with the outgroup Heinemannomyces sp. Posterior probabilities which are equal and above 80 % are indicated. The 95 % highest posterior density of divergence time estimation is marked by horizontal bars. Species sampled from GMS and Europe are in red and blue, respectively; new taxa are in bold.