The hemlock species known as 'Tsuga sieboldii' is a type of coniferous tree that has sacred meaning to adherents of some pagan religions and symbolizes protection and healing. There are a few different species of plant that bear the name hemlock; each one may have its own symbolic meaning.
There is another form of hemlock, 'Conium maculatum,' that was used as a poison for executions. This toxic nature has caused the hemlock to be associated with death and danger. The ancient Greek philosopher Socrates was famously forced to drink hemlock poison when he was sentenced to death for the supposed impiety of his philosophy. This event is depicted in a famous painting by Jacques-Louis David.