Greek Mythology: Origin of Aconite

Aconite is a plant.

Description
Aconite, also known as Wolfsbane and Monkshood, is a plant that grows purple or blue flowers and is about a meter tall. It is extremely poisonous which is how the ancient Greeks used it. It tends to grow on rocky ground, rather than in dirt.

Heracles' Final Labor
Heracles' final labor was to fetch Cerberus from the Underworld. The aconite plant sprang up wherever the spit of Cerberus touched the ground.

Poison of Medea
Theseus returned to Athens to find his long-lost father King Aegeas. King Aegeas' wife, Medea, knew that Theseus was his son so she tried to give him a cup of wine with aconite in it. Aegeas saw Theseus with the sword that he left him so he would know that he was his son. Aegeas then knocked the cup of deadly wine from Theseus' hands.