Hypholoma fasciculare, commonly known as Sulphur Tuft, is a wood-decay fungus frequently found on logs of deciduous trees. It is characterized by its dense clusters of  distinctive sulphur-yellow to greenish-yellow mushrooms, with caps that measure 2-6 cm in diameter. The cap is convex to flat with a smooth surface and often has a slightly darker centre. The gills are crowded, initially yellow, but turn greenish-black as the spores mature. The stipe - or stem - is yellow and fibrous. This fungus is widespread, thriving in temperate forests across North America, Europe and Asia. It plays a significant role in forest ecosystems by decomposing lignin and cellulose in dead wood, thus recycling nutrients back into the soil.  Sulphur Tuft mushrooms are toxic to humans, containing compounds like fasciculol E, which cause severe gastrointestinal distress. Correct identification is crucial, as it can be confused with some edible mushrooms.