How to tell Petticoat mottlegill from Liberty cap

The cap is 1.5 to 4 cm across, occasionally 5 cm. It starts egg-shaped or bluntly conical, then becomes bell-shaped and never flattens. It's grey-brown, pale brown or greyish, sometimes with reddish or olive tints and a darker centre. In dry weather it pales and often cracks.

Young caps have white triangular veil teeth hanging from the rim. They rub off easily, so older caps may have none.

The cap is small, 1-2.5 cm across, sharply conical or bell-shaped with a pronounced pointed knob in the centre, which gives it the epithet semilanceata ("half-lance-shaped"). The cap skin is smooth, slimy in wet weather, dry with lengthwise grooves in dry weather. The colour is ochre-cream; olive-brown with a greenish tint when wet, pale cream when dry. The pointed central knob is the most characteristic diagnostic feature.

The gills are attached and crowded, grey at first, then mottled grey and black as the spores ripen in patches, and finally black. The gill edges are white.

The spore print is black.

The gills are attached to the stem and moderately crowded. In young mushrooms they're greyish-cream, darkening to purplish-blackish as the spores mature. The spore print is dark purple-black, a diagnostic feature of the genus Psilocybe.

The stem is 5 to 12 cm tall and 2 to 4 mm thick, long and slender for the cap, the colour of the cap or paler, finely powdered at the top and darkening towards the base. It's hollow and brittle, with no ring.

The stem is 5-10 cm tall and 0.15-0.3 cm thick, so very long and thin, often curved. The colour is yellow-cream to light brown, and the surface is smooth with fine lengthwise fibres. There is no ring, and this is essential. It often turns blue when damaged, a characteristic psilocybin reaction and one of the diagnostic tests.

The flesh is thin and pale.

The flesh is very thin, soft, yellowish to greenish. It quickly turns blue to blue-green when cut or damaged, a characteristic reaction of psilocybin alkaloids on contact with air. The smell is faint, mealy in some populations.

The smell isn't distinctive.

Faint, neutral or mealy, nothing distinctive. The smell is not a warning sign.