The Question:
How do you identify Poison sumac?

Submitted by: Ellie, MA, USA

The Short Answer: Poison sumac is a large shrub or small tree found in wet areas. It has compound leaves with 7-13 smooth-edged leaflets, as shown in figure 1. The stalk of the compound leaf is reddish. To differentiate poison sumac from other common sumacs, count the number of leaflets. Staghorn and smooth sumac have more than 13 leaflets, and the leaflets have a serrated edge. Dwarf sumac can have the same number of leaflets as poison sumac, but the leaf stalk has “wings”, as show in figure 3, in keeping with its alternate name, winged sumac.

More Info: Poison sumac, Toxicodendron vernix, is part of the large Anacardiaceae plant family. The Anacardiaceae includes cashew, mango, pistachio, and the “poisonous” plants so painfully familiar to North Americans. Poison sumac is in the same genus as Eastern poison-ivy, Western poison-ivy, Eastern poison-oak, and Western poison-oak, which means it’s closely related to them. They all produce urushiol, the oil that causes such an agonizing allergic reaction. But the plants are probably not trying to irritate your skin. Most likely they produce urushiol to fend off sap-sucking insects. It’s not clear why people are so susceptible to urushiol. Birds and bears eat the berries of poison sumac, poison-ivy, and poison-oak and expose themselves to the leaves with no sign of harm.

Other sumacs such as staghorn sumac, Rhus typhina, are also members of the Anacardiaceae, but don’t necessarily produce urushiol. Poison sumac, while it looks more like harmless staghorn sumac than like poison-ivy and poison-oak, is actually more closely related to its three-leafed poisonous relatives. When biologists use DNA sequences to figure out the relationships between the plants in the genus Toxicodendron, the relationships between Eastern poison-ivy, Toxicodendron radicans, Western poison-ivy, Toxicodendron rydbergii, Eastern poison-oak, Toxicodendron pubescens, and Western poison-oak, Toxicodendron
diversilobum, the relationships are not clear, which suggests that there has been significant hybridization between them over time. This makes it difficult to determine where one species stops and the next begins. In any event, they can all make you miserable, so avoid them if you can.

Trivia:
The cashew plant, Anacardium occidentale, also produces urushiol, and cashews have to be handled and processed carefully to separate the cashew nut from the fruit and remove any urushiol from the nut.

References:

This site is really useful for identifying poison sumac, poison ivy and poison oak:  http://www.poison-ivy.org/poison-sumac

Ask a Naturalist® (November 25, 2020) How do you identify Poison Sumac?. Retrieved from http://askanaturalist.com/how-do-you-identify-poison-sumac/.
"How do you identify Poison Sumac?." Ask a Naturalist® - November 25, 2020, http://askanaturalist.com/how-do-you-identify-poison-sumac/
Ask a Naturalist® June 17, 2010 How do you identify Poison Sumac?., viewed November 25, 2020,<http://askanaturalist.com/how-do-you-identify-poison-sumac/>
Ask a Naturalist® - How do you identify Poison Sumac?. [Internet]. [Accessed November 25, 2020]. Available from: http://askanaturalist.com/how-do-you-identify-poison-sumac/
"How do you identify Poison Sumac?." Ask a Naturalist® - Accessed November 25, 2020. http://askanaturalist.com/how-do-you-identify-poison-sumac/
"How do you identify Poison Sumac?." Ask a Naturalist® [Online]. Available: http://askanaturalist.com/how-do-you-identify-poison-sumac/. [Accessed: November 25, 2020]