King Alfred's Cake

Daldinia concentrica

The inedible fungus ''Daldinia concentrica'' is known by several common names, including King Alfred's Cake, cramp balls, and coal fungus. It can be found in North America, South America and Europe, where it lives on dead and decaying wood, especially on felled ash trees. It is a common, widespread saprotroph.

The fungus is ball-shaped, with a hard, friable, shiny black fruiting body 2 to 7 centimeters wide. It resembles a chunk of coal, which gives it several of its common names, including coal fungus and carbon balls. According to legend, King Alfred once hid out in a countryside homestead during war, and was put in charge of removing baking from the oven when it was done. He fell asleep and the cakes burned. ''Daldinia concentrica'' is said to resemble a cake left to this fate.

The flesh of the fungus is purple, brown, or silvery-black inside, and is arranged in concentric layers. Each layer represents a season of reproduction. The asci are cylindrical and arranged inside the flask-shaped perithecium. When each ascus becomes engorged with fluid it extends outside the perithecium and releases spores.

''D. concentrica'' contains several unique compounds, including a purple pigment from a perylene quinone and a metabolite called concentricol, which is oxidized squalene. Many types of insects and other small animals make their home inside this species of fungus.