Hypholoma fasciculare is commonly known as the sulphur tuft or clustered woodlover (in German: Grünblättriges Schwefelköpchen, lit. “green-leafed little sulphur head). It is a very common woodland mushroom that often appears in places where hardly any other mushrooms are to be found. It is saprophagic (i.e. feeding off detritus) and grows in large clusters on rotting tree stumps, dead roots or dead wood in general. Sometimes these clusters are so tightly packed that the caps are unable to expand
Fascicularis means “bundled” or “clustered”.
It has small, tight gills that are yellow when young, but darken to a very distinctive green (hence the German name “grünblättrig”, the “leaves” in question are the gills).
This mushroom is bitter and poisonous and can cause cramps, diarrhea, vomitting, nausea and impaired vision.
Funnily enough this mushroom has a doppelganger that counts among the best edible mushrooms of all:
Kuehneromyces mutabilis, commonly known as the sheathed woodtuft. It looks like Hypholoma fasciculare in everything except for a row of tiny “scales” just beneath the cap on the stem:
If only the caps are collected, even an expert cannot tell the two mushrooms apart.