This is among the deadliest mushrooms one can come across.
Galerina is a genus of saprobic fungi which has sections known to contain significant amounts of the toxin named for another genus, Amanita.
The group of toxins in question are 'amatoxins' which interfere with RNA polymerase II. Alpha-amantin and Gamma-amantin cause the body to stop being able to produce proteins!
The human body has a roughly one week supply of necessary proteins and after this time has lapsed, the toxins will cause both liver, kidney failure and eventual excruciating death.
Poisoning can ONLY occur after SWALLOWING the mushrooms. ALL mushrooms can be tasted, spit out. To cause serious damage or death, an individual would have to make the error of eating a dozen or two of these.
The only known treatment is derived from the Milk Thistle plant and is called 'Silibinin' which need be administered very shortly after ingestion of Amatoxin containing species.
When harvesting mushrooms it is very important to be able to identify this species. Here are a few notable traits:
Brown or rusty brown spore deposit which can be seen on both the gills, since these are older specimens, as well as the 'annulus' or ring around the upper portion of the 'stipe' or stem.
These are typically small fruitbodies in the range of ~2 to ~ 8 cm 'pileus' or cap which a narrow stipe roughly 1 cm thick. The stipe may start off silvery white with small fibrils coming off of it, darkening over time to a brown/orange/black.
The 'lamellae' or gills are slightly attached to the stipe and begin to run down it.
The pileus is 'hygrophanous' meaning it changes color when wet. When dry they are a dull tan, when moist a deep brown.