Eriocybe chionea Vellinga, in Vellinga et al., Mycologia 103(3): 504 (2011)
Pileus 20–28 mm, plano-convex with deflexed margin to more or less applanate set with cottonwool-like broad fluffy warts, composed of hyphae, pure white, with margin exceeding lamellae. Lamellae, l = 0–1(–3), crowded to crowded free, not remote from stipe, rounded near stipe, ventricose, 2–3 mm wide, (pale) cream white, with white, even to subtly cystidiose edge. Stipe 18–22 x 4 mm, slightly narrower at apex, white, pale cream white and smooth above annular zone, below that with white fluff in bands or all over floccose, hollow. Annulus a widened white cottony, slightly flaring zone on stipe. Context white in pileus and stipe, thick in pileus. Odor spicy, camphor-like, totally different from any other species (ecv3560); strongly unpleasant, like rancid coconut (ecv3616). Taste not tested.
Basidiospores [40,2,2] in side view 4.0–5.2 x 2.3– 3.1 µm, avl x avw = 4.5–4.6 x 2.9 µm, Q = 1.45–1.85, avQ = 1.55–1.6, ellipsoid to oblong, in frontal view ellipsoid to oblong, slightly thick-walled, smooth, without germ pore, often with guttule, congophilous, immediately dextrinoid in Melzer’s reagent, in cresyl blue with non-colored wall, and a pink line around blue contents, with blue walls in cotton blue. Basidia 13–16 x 5.0–7.0 µm, four-spored, with scattered twospored basidia. Lamella edge sterile, set with cystidia. Cheilocystidia 12–28 x 4.5–10 µm, cylindrical to narrowly clavate in one collection (ecv3616), and clavate, pedunculate fusiform, to narrowly clavate in the other (ecv3560). Pleurocystidia absent. Hymenophoral trama composed of cylindrical to inflated noncolored hyphae, 7–12 µm diam. Pileus covering a big felt-like mat composed of slightly inflated to cylindrical, non-pigmented hyphae with elements 45–100 x 9.0–17 µm on top, with a big layer of narrow, 2.0– 4.0 µm wide cylindrical, non-pigmented hyphae. Stipe covering as pileus covering. Clamp connections absent.
Habitat and distribution: Solitary, terrestrial, on road verge in mixed rain forest and on steep vertical red clay bank, 900–1300 m, in northern Thailand, fruiting during the rainy season (Jun–Jul). Found only twice so far.
Index fungorum number: IF518496
Notes: Eriocybe chionea is characterized by the small relatively short-stiped white felted-woolly basidiocarps with an unusual odor among the Agaricaceae; microscopically it is defined by the combination of spore size, narrowly clavate to clavate-fusiform cheilocystidia, the thick pileus covering composed of wide parallel hyphae and the absence of clamp connections.
Agaricus subg. Lanagaricus Heinem. comes close morphologically but has brown spores. Agaricus trisulphuratus Berk., the type species of this subgenus, has basidiocarps covered in pointed orange scales, which are composed of parallel cylindrical hyphae with incrusting pigment, a regular hymenophoral trama composed of cylindrical hyphae up to 7 mm diam and subutriform cheilocystidia (Vellinga pers obs). Species of Agaricus subg. Conioagaricus Heinem. also resemble Eriocybe because they have a velvety, powdery or squamulose pileus covering composed of ellipsoid to inflated short cells, which often have incrusted cell walls or an ornamentation composed of warts or spines (Heinemann 1956), but the stipe lacks this covering and of course the spores are brown. This subgenus has, as does Agaricus subg. Lanagaricus, a mainly tropical distribution.
Figure 1. rpb2 phylogeny of the Agaricaceae inferred by maximum likelihood (ML) analysis. Numbers at internodes refer to confidence estimates based on 100 rapid ML bootstraps (only those ˃ 70 are given). Coniolepiota and Eriocybe are highlighted, and main clades are indicated. Amanita brunnescens and A. muscaria, Hebeloma olympianum, Strobilomyces strobilaceus and Tubaria vinicolor are outgroup taxa.
Figure 2. Phylogeny of Agaricus and satellite genera in the Agaricaceae based on nrITS sequences, inferred by maximum likelihood (ML) analysis. Numbers at internodes refer to confidence estimates based on 100 rapid ML bootstraps (only those ˃70 are indicated). Coniolepiota and Eriocybe are highlighted, and genus Agaricus and the Agaricus clade indicated. Leucoagaricus barssii and La. leucothites are outgroup taxa.
Figure 3. A phylogeny of the Agaricaceae inferred by maximum likelihood (ML) analysis of a combined nrLSU, rpb2, tef1 and nrITS dataset. Numbers above branches refer to posterior probability scores before the / (those ˃ 0.94 are given) and confidence estimates based on 100 rapid ML bootstraps (only those . 75% are indicated) after the /; the numbers below the branches are bootstrap support values from the parsimony analysis (˃ 75%). Thick branches have a posterior probability ˃ 0.94, and both bootstrap values ˃ 75.