Image: Jukka Vauras

Mycologists (those folks whose business is to study fungi) have called on the public for help in adding data on the occurrence and range of the witches' cauldron (Sarcosoma globosum) to their national mushroom atlas.

The species is rare, with only 80 reported observations in Finland since 1915.

Since it is so uncommon, there are gaps in scientists' knowledge of the witches' cauldron. When found, its typical habitat is in mossy old-growth spruce forests along rivers and brooks where it grows in chalky soils.

The witches' cauldron mushroom has a general barrel shape, is about the size of a fist, with a central cup or caldron filled with a jelly-like substance. Dark brown, it starts growth as a ball. Late in its life cycle it collapses into a thin, flat form with ragged edges.

The witches' cauldron is not poisonous, but it is not considered suitable for consumption.

Researchers are asking anyone who discovers one not to pick it, but to take a photograph of the mushroom in its natural surroundings. Photos and observations can be filed on an information form with the Finnish Biodiversity Information Facility.

Log-in instructons for the service in English can be found here.