Wolfsbane, which is actually in the buttercup family of plants, is a poisonous perennial herb. The plant grows in partial shade and has unusual delicate clusters of typically purple or blue hooded flowers which have 2 – 5 petals. In many legends, wolfsbane has an effect on werewolves. The smell is supposedly so sickening to a werewolf that it will keep a werewolf at bay. (Kind of similar to the effect of garlic with vampires). To be clear however, legends do not cite the plant as being able to kill the werewolf.
Other sources also indicate wolfsbane can be used as a test to tell if someone is a werewolf by seeing if the plant’s flower casts a yellow shadow on the person’s chin.