Agaricus fimbrimarginatus

Agaricus fimbrimarginatus Linda J. Chen, Callac & K.D. Hyde 

Index Fungorum number: 818049, Facesoffungi number: FoF 02285.

Pileus 4 cm diam, 3 mm thick at disc; applanate and slightly depressed at disc; surface dry, with purplish fibrils, densely at disc, radially arranged elsewhere, and sparse towards the margin, on a dirty white background. Margin straight, shortly exceeding the lamellae, with appendiculate remains of the annulus. Lamellae free, crowded, 3 mm broad, with intercalated lamellulae, ventricose, pinkish to brown with time. Stipe 47 × 7–8 mm, cylindrical with a slightly bulbous base, surface above the ring smooth, below the ring fibrillose, white, strongly flavescent when bruised. Annulus simple, membranous, superous, white, fragile. Context firm, white, flavescent when cut. Odour strong of almonds.

Spores (4.4–)4.5–4.9 × (2.9–)3–3.3 µm, (x = 4.7 ± 0.11 × 3.2 ± 0.09 µm, Q = 1.36–1.59, Qm = 1.46 ± 0.01, n = 20), ellipsoid, smooth, brown, thick-walled. Basidia 12–17 × 5–6 µm, clavate to broadly clavate, hyaline, smooth, 4-spored, rarely 2-spored. Cheilocystidia 15–26 × 8–12 µm, simple, pyriform or broadly clavate, with yellowish pigments, smooth. Pleurocystidia absent. Pileipellis a cutis, composed of cylindrical hyphae of 4–9 µm wide, not or slightly constricted at the septa, with brownish pigment. Macrochemical reactions — KOH reaction positive, yellow. Schäffer’s reaction positive, reddish on dry specimen. (Figs. 1–2)

Etymology: Refers to the appendiculate remains on the pileus margin.

Habitat: Solitary on soil, in grassland along roadside.

Material examined: THAILAND, Chiang Mai Prov., Mae Sa, 25 June 2012, P. Callac & J. Chen, LD201250 (holotype MFLU12-0891).

    Notes: Agaricus fimbrimarginatus is characterized by a pileus surface covered with purplish fibrils, simple cheilocystidia and small spores less than 3.5 μm wide. Several members of A. sect. Minores resemble A. fimbrimarginatus by exhibiting a reddish brown to purplish brown, fibrillose pileus surface, such as, A. brunneolus, A. dulcidulus, A. gemlii, A. megalosporus and A. patris. However, A. brunneolus, A. gemlii, A. megalosporus and A. patris are easily distinguished by their larger spores (wider than 3.5 μm on average). Agaricus dulcidulus differs in its smaller spores (4.3 × 3 μm on average). According to the phylogenetic analyses, A. fimbrimarginatus shows close affinities to A. robustulus. However, the latter species differs in its robust sporocarps and larger spores and molecularly has four nucleotides in difference in the ITS sequences, two differences in LSU and with more than 20 differences in tef-1α sequences.

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 are marked by horizontal bars. Species sampled from GMS and Europe are in red and blue, respectively; new taxa are in bold.