Mushrooms

Mushrooms are occasionally used in cocktail ingredients such as candy cap syrup. Mushrooms are dangerous to forage without identification expertise, as some are extremely poisonous. 

Further Reading:

"Mushroom Poisoning: Don't Invite "The Death Angel" to Dinner" National Poison Control Center [link]

"How Do I Tell If a Mushroom Is Safe to Eat?" LifeHacker [link]