Walking through a woodland you will often see ash trees with black blobs on them, usually on dead branches or on branches that have fallen off the tree. This has several names including coal fungus or cramp balls or King Alfred's cakes. These hard, semi-spherical black lumps are usually about 3-4 cm in diameter and are the fruiting bodies of a fungus, which decays the dead wood of the ash tree. The photo shows the inside of one of these pictured on a log in my back garden - not on an ash tree.
Legend has it that King Alfred, when in hiding from the Danes, once burnt some cakes by failing to take them out of the oven. These fungal growths, which look as if they have been burned, are a reminder of his poor cooking and hence are nicknamed “King Alfred’s Cakes”, but their correct Latin name is Daldinia concentrica. They grow in either a black form or a dark brown – perhaps the lighter colour shows that Alfred did remember to take out the cakes before they were totally incinerated!
The black variety can be very useful for lighting fires because the inner flesh, once dried out, can be easily lit from a “firesteel” (this is an “artificial flint” which creates a spark for starting fires, much used in bushcraft). A spark will ignite the flesh of the fungus and, although it burns slowly like a barbecue briquette, once it has been lit one can transfer the glowing part to a ball of tinder and get a flame started.
Like so much in woodlands, once you know to look for these, you might see them quite often.