A couple of weeks ago I wrote about the Giant Puffball, Calvatia gigantea. It is one of several species of puffball that are good to eat, though all of them are smaller than the Giant Puffball.
But there is a common species of fungus that is superficially similar, which you shouldn’t eat – the Common Earthball, Scleroderma citrinum.
When I say superficially similar, I mean that both puffballs and the Common Earthball are spherical and sit on the ground without gills, pores or a stem. The Common Earthball is much wartier than any puffballs, with a thick and tough skin, covered with coarse and irregular scales. The skin is initially white, cream or yellow but may turn ochre-brown or green as it ages. (Citrinum refers to the citrine yellow colour of the skin.)
If you cut a mature Common Earthball open you will see the dark purply brown mass of spores inside; on really young specimens these are off-white, soon turning marbled brown and white. Puffballs have a pure white mass of spores when they are suitable to eat. You can squeeze a puffball like a marshmallow but the Common Earthball is much tougher and its skin will crack if you press hard enough (Scleroderma means ‘hard skin’). Sniff a Common Earthball and you may detect a slight unpleasant smell of gas; true puffballs smell pleasantly “mushroomy”.
According to the Nature’s Secret Larder website, unscrupulous restaurants have been known to remove thin slices from the dark centre of Common Earthballs, soak them in truffle oil and serve them as real truffles.
This is a bad thing, as the Common Earthball is poisonous, although not in the league of the highly poisonous fungi such as Death Cap. If you eat it you are likely to experience gastrointestinal distress. (Wikipedia says that a few very sensitive individuals may experience lacrimation, rhinitis and rhinorrhea, and conjunctivitis from exposure to its spores.) In the United States the fungus is called the Pigskin Poison Puffball, a rather apt name.
Common Earthballs are indeed common and can be seen in autumn and early winter, in woodlands, on heathland, on shaded earth banks and on woodland and forest tracks. (The photographs above were taken in Blean Woods in Kent but I first saw the fungus many years ago at Buxton Heath, north of Norwich.)
Common Earthballs and puffballs have been lumped together in the gasteromycete fungi (the stomach fungi), but Common Earthballs are actually more closely related to boletes than puffballs, in particular boletes of the genus Gyroporus. If you want to know more, the First Nature website is a good place to start. It has some excellent photographs.