Daldinia concentrica has various common names ie Cramp Balls and King Alfred's Cakes.
It grows on a variety of trees but does favour beech and ash and looks like small black balls of hard coal. When young it is reddish brown with a greyish tinge, turning black in full maturity. It can reach up to 7cm in diameter. The flesh consists of concentrical zones.
Yesterday I visited Bottom Wood, near Matlock, Derbyshire. I've seen Daldinia concentrica on many occasions over the years but have always wanted to see the 'internal' concentrical ridge/zone structure. Easier said than done, as the fruit body is extremely hard and I always thought a hack-saw! would be required to cut one in half.
The Daldinia I came across yesterday and touched, crumbled in half and there before me was the concentrical structure I had wanted to see for many years. What struck me is that they look just like the 'rings' on tree trunks that have been cut down and are counted to ascertain the age of the tree. On further research it seems that each zone layer on the Daldinia is representative of each season of growth. I counted eight zones so presumably this example has had eight growing seasons.
Below is a photograph showing the concentrical zones and a mature example.