|Yellow Fieldcap (Bolbitius titubans)|
With a little help from Fungus UK, it would seem that this delightful little fungus, found in Pembrey Forest yesterday is Yellow Fieldcap, Bolbitius titubans, also known as the Egg Yolk Fungus. The First Nature website says:
This colourful little mushroom of rich grassland and roadside verges is one of the shortest-lived of all mushrooms. It goes from a yellow 'egg on a stick' via a pinkish parasol stage to a mid-to-dark brown or, in hot dry weather, light ochre mushroom in less than a day.