Humpback brittlegill or Pirate brittlegill

The cap is 3-8 cm across and, when young, conical-convex with a sharp papillate bump in the centre, a diagnostic feature. With age it becomes flat-convex, but the bump stays. The skin is smooth, slimy and sticky in wet weather, dry and matte in dry weather, and peels 1/3 of the way to the centre. It's dark violet, violet-azure or purple-chestnut, richer in the centre, paler toward the edge, fading to greyish. Mature caps have fine radial grooves at the edge.

The cap is 3–8 cm across, occasionally up to 10 cm. It starts convex, soon flattens and finally becomes depressed in the centre.

The colour is violet, dark purple, lilac or wine-red, sometimes greyish pink. The centre is darker at first but soon fades to dirty pink, olive or yellowish, often with bright yellow spots. A form with an entirely yellow cap has also been described.

In wet weather the skin is slightly greasy, but it dries quickly from the margin and then looks matt and velvety, as if dusted. The skin peels easily, about a third of the way to the centre.

The gills are attached or free, moderately crowded, fleshy and brittle. They're whitish at first, becoming cream-ochre-yellowish with age as the spores mature. The spore print is yellow-ochre, a diagnostic feature.

The gills are cream or pale yellow at first and a rich ochre-yellow when mature. They are fairly crowded, becoming more distant with age, attached to the stem and joined by cross veins near the base.

The spore print is pale yellow to ochre. A white print points to a different russula, such as the charcoal burner or the purple brittlegill.

The stem is 4-8 cm tall and 1-2 cm thick, firm and cylindrical, hollow in older mushrooms. It's whitish, often with a faint violet-pink tint low down, and its surface is smooth with fine lengthwise wrinkles. No ring.

The stem is 3–8 cm tall and 1–2 cm thick, cylindrical or slightly club-shaped. It is pure white, rarely pinkish, and yellowish in wet weather.

Young stems are firm; old ones become chambered or hollow, especially at the base. There is no ring and no volva.

The flesh is firm, brittle and white, and slowly turns yellow where cut. The smell is faint and pleasant, with a hint of coconut and fruit in young mushrooms; the taste is mild and slightly bitter, especially in the stem, but not burning-acrid, which sets it apart from its poisonous relatives.

The flesh is white, yellowing with age and lilac just under the cap skin. It is brittle, as in most russulas, and does not change colour when broken. Field guides describe the taste as mild and sweetish.

A faint, pleasant fruity-coconut smell in young mushrooms, turning neutral with age.

The key feature of the species: the base of the stem smells of iodoform, an old-fashioned antiseptic. The smell stays at the bottom of the stem and is not always obvious, so it is worth checking several specimens. The cap and gills have no particular smell.