Porcelain fungusMucidula mucida

The porcelain fungus (Mucidula mucida, long known as Oudemansiella mucida), also called the poached egg fungus, looks as if it's made of fine china: glossy, translucent white caps covered in slime, growing in tufts on dead and dying beech. Underneath it has broad, widely spaced white gills, and its slim stem carries a clear white ring. It's hard to mistake for anything else as long as you remember one thing: it always grows on wood.

How do you identify porcelain fungus? The cap is 2 to 8 cm across, greyish when young and later snow white and translucent, often with a faint ochre flush in the centre. In wet weather it's coated in thick, clear slime. The gills are broad, widely spaced and white. The stem is slim and tough, often curved so that the cap stays level even on the side of a trunk, and has a white, membranous ring. The spore print is white, and there's so much of it that it can dust everything around.

Where does it grow? Almost always on beech: on fallen trunks, stumps and branches, and on dead branches high in living trees, from which the caps sometimes drift down on windy autumn days. It occasionally grows on oak. It's common wherever there's beech. Look for it from late summer to late autumn, with most finds in early and mid-autumn, and the odd one in summer or early winter.

Is porcelain fungus edible? Only after preparation. Wash off the slime thoroughly, cut away the tough stems and cook it well. It has little flavour and thin flesh, so it's not a mushroom worth seeking out for the pan and is best mixed with other mushrooms. Most guides treat it as edible once prepared, though one Dutch key rates it as suspect, and we found no confirmed poisonings.

What can you mistake it for? Oyster mushrooms are also pale and grow on wood, but they aren't slimy, have short, off-centre stems and crowded gills running down the stem. The veiled oyster has a ring, but its cap is dry and scaly. More importantly, caps that have fallen from the canopy end up in the leaf litter, and fruit bodies on buried wood can look as if they grow from soil. So only pick specimens attached to wood, and always check the stem base. A white mushroom with a ring growing from the ground under beech is not a porcelain fungus and could be a deadly amanita such as the destroying angel, with crowded free gills and a sac at the base. Angel wings (Pleurocybella porrigens) are white too, but have little or no stem, crowded gills and grow on conifer wood; in Japan they have been linked to fatal poisonings. Honey fungus has a ring and grows in tufts on wood, but its caps are honey brown and scaly, never white and slimy.

In the 1960s, scientists in Czechoslovakia isolated an antifungal substance, mucidin, from cultures of this mushroom and even made an ointment from it for fungal skin infections. Mucidin later turned out to be identical to strobilurin A. Natural strobilurins became the model for a whole class of modern farm fungicides, first released in 1996 and now among the most widely sold in the world. These compounds probably also help the porcelain fungus keep other fungi off its log.