Puffballs are fungal fruiting bodies that differ from the usual mushrooms and toadstools. They usually form spherical structures which mature to contain masses of reproductive spores. The spores are released through a ruptured aperture on the top of the puffball. Rain needs to fall onto the fungus or impact is needed from some other source to impart enough pressure to cause some of the spores to puff out.
An exception to this form is the pestle puffball - Calvatia excipuliformis. This fungus seems unusually common around the Midlands this year. This fungus produced hyphae (long strands of interconnected cells) which permeate dead timber and leaf mould on the forest floor. When they produce their fruiting bodies, the puffball spheres are supported on a solid pedestal, which is unusual for a puffball. The surface of the fungus is covered in small and uniform bobbles which makes them easily identifiable. The surface flecks will rub off as they are formed by the fragmented veil (outer membrane, which shatters as the fruiting body inflates).
Here are a pair of pestle puffballs and the one on the right is mature, having ruptured to release spores from the very top of the head. These fungi are growing in beech forest in Staffordshire, though they can equally be found on heathland. A similar species - Calvatia utriformis - grows in meadows and is a more compact form, but I have not yet seen that species this year.