With fungi being something of a challenge to identify unless you specialise in them it is always good to find one that has a distinctive feature. The two tone cap here, dark around the edges and lighter in the centre marks this out as the common stump brittlestem (Psathyrella piluliformis).
A widespread and common species it is found in autumn growing on decaying wood of mainly beech and oak trees. It starts with a conical cap which gradually flattens out with age and the differentiation in colour becomes slightly less obvious. It usually grows in a small cluster.
It apparently has a rather bitter taste so it is best left where it is to spread its spores and create new fungi.Psathyrella piluliformis: the common stump brittlestem