Hypholoma fasciculare

Hypholoma fasciculare, commonly known as the sulphur tuft or clustered woodlover, is a common woodland mushroom, often in evidence when hardly any other mushrooms are to be found. This saprotrophic small gill fungus grows prolifically in large clumps on stumps, dead roots or rotting trunks of broadleaved trees. The "sulphur tuft" is bitter and poisonous; consuming it can cause vomiting, diarrhea and convulsions....read more on Wikipedia.