Cystolepiota bucknallii

The fruit body of Cystolepiota bucknallii is a relatively small, thin-fleshed agaric. The cap is at first hemispherical and becomes convex with maturity. It bears a broad central umbo and reaches 5 cm in diameter. The cap cuticle is white with a lilac or violet tinge. The gills are crowded and not attached to the stipe. Their colour is cream to pale yellow. The stipe is comparatively long (up to 6 cm), slender and bare, tinged lilac or violet except for the uppermost section where it is pallid. Both cap and stipe are covered with a mealy powder which is easily rubbed off. All parts are fragile. The flesh is white, thin and does not bear a distinctive taste.[2][3]

The spore mass is white. With the aid of a light microscope, the spores are seen ellipsoid, smooth and colourless. When Melzer's reagent is applied, the spore walls barely stain; hence, the spores are weakly dextrinoid. Their dimensions are 7.5–10 µm by 1–3.5 µm.[2][3]

Cystolepiota bucknallii has a characteristically pungent odour, reminiscent of coal gas or sulphur. Indole is present in this as well as in other similar-scented fungi: Tricholoma inamoenum, Tricholoma lascivum, Tricholoma sulphureum and others.[4]

While its edibility is not known, there exists speculation about possible toxicity.[2][3]

C. bucknallii has been recorded in various countries in central and northern Europe including France, Belgium, Switzerland, Austria, Germany, Denmark, Norway, Sweden and Russia.[5] It is a terrestrial decomposer which occurs in deciduous forests with moist, calcareous soils rich in nutrients and especially nitrogen. Fruit bodies appear in autumn.[3] Moreover, C. bucknallii is an uncommon or rare fungus whose populations are found in communities harbouring a diversity of other rare species. A population may serve as an indicator for rich, conservable biotopes.[6]

Cystolepiota bucknallii in Index Fungorum

• Images of C. bucknallii at BioImages (UK)