Butter cap or Common bonnet

Cap 2-6 cm across; in young mushrooms bell-shaped or conical with a sharp central bump, becoming convex with age while keeping the same bump. Color gray-brown, darker to dark gray in wet weather, paler to beige in dry weather. The surface is smooth, with fine radial grooves from the margin to the center (the gills show through). The cap margin is thin and often splits in old mushrooms.

Cap 3-7 cm across, when young convex, becoming with age flat-expanded with a small umbo in the center (a characteristic shape). Cap skin smooth, with a pronounced buttery-greasy sheen in wet weather — hence the name. Strongly hygrophanous: in wet weather — dark chestnut-brown in the center, lighter toward the margin; when dry — light creamy brown, ochre and faded. The margin is even, thin, often with lengthwise striations where the gills show through.

Gills — whitish when young, turning pinkish with age, moderately crowded, with distinctive cross-veins between them. Attachment to the stem notched (adnexed). Spore print white.

Gilled hymenophore — the gills are adnate or free from the stem, crowded, thin, whitish to cream, turning cream-pink with age. Spore print pale pink to cream — a typical trait of the genus Rhodocollybia ("pink Collybia").

Stem 5-12 cm tall, 0.3-0.6 cm thick, long, thin, cylindrical, fragile. Color pale grayish-white above, darker toward the base. The surface is smooth. The stem base is often wrapped in whitish, felty mycelium — a characteristic feature of the species on mossy stumps.

Stem 3-7 cm tall, 0.3-0.8 cm thick, cylindrical, noticeably thickening toward the base (often with a characteristic "root-like" extension into the substrate). Color ochre-brownish, darker toward the base. Surface smooth, with lengthwise fibers. The stem flesh is tougher and more fibrous than the cap's.

Flesh thin, watery, whitish, more fibrous in the stem. Does not change color when cut. Smell faint; in some populations slightly mealy or radish-like. Taste mild, with a light mealy note.

Flesh thin and tender in the cap, tough and fibrous in the stem. Color whitish to cream. Doesn't change color when cut. Smell faintly mushroomy, taste mild, neutral, normally without bitterness.

Faint; in some populations with a note of flour (like fresh bread) or radish. Not distinctive enough for a confident ID.

Faint, neutral, mushroomy, nothing distinctive.