Poison sumac is a plant that is notorious for causing allergic reactions when it comes in contact with human skin. It belongs to the Anacardiaceae family and is also known as Toxicodendron vernix. This plant is commonly found in wetlands and swampy regions across the U.S. and is considered one of the most toxic plants in North America. Some synonyms for poison sumac include thunderwood, poison elder, swamp sumac, and poison dogwood. It is important to avoid contact with this poisonous plant to prevent inflammation, rash, or blisters on the skin. If you come in contact with poison sumac, wash the affected area with soapy water immediately.