Beware of Poison Sumac (Rhus vernix)
Years ago, as a newly minted Natural Resources Steward graduate (formerly the Tree Stewards program), I discovered a pretty, bright red compound leaf on a small shrub growing along the side of the road. It was late summer – a first sign of fall. The leaf was unusual, unlike any I had ever seen. Challenged and excited by this new discovery, I picked a leaf and raced home to figure out what it was. I eagerly studied my new collection of tree ID books, but I dropped my prized leaf in horror when I found it in George W. Symonds’ The Shrub Identification Book. The photo of the poison sumac leaf was identical to mine!
I am extremely sensitive to poison ivy, which I first contracted after unwittingly pulling the vines out of trees. The unbearable itchy rash covered my whole body and lasted months. So I knew I was in trouble again, because poison sumac has the same toxic oil or phenol, urushiol, that is found in poison ivy. Because my prior cases seemed to increase my sensitivity, it spread all over my body. In her book Trees and Shrubs of New England, Marilyn Dwelley says that sumac reactions are worse than poison ivy. I can attest to that!
Fortunately, poison sumac grows almost exclusively in swamps and bogs where people are not likely to go. It turns out my roadside sprout was across the road from large poison sumac shrubs growing at the edge of a swampy area. In June it produces clusters of tiny white flowers at the branch tips that become large clusters of waxy green berries in July and turn white in the fall. Birds had likely spread the seeds across the road. In fact, many wildlife species will eat berries of poison sumac without contracting the same itchy rash most humans will suffer by just touching the plant! So, when poison sumac is found in an out-of-the-way location, it’s best left alone to provide forage for wildlife.
More recently, I’ve seen poison sumac spreading beyond the swamp borders in my area. While tossing some dead raspberry canes along the edge of my woods the other day, I noticed a horrible mess of oriental bittersweet, black swallowwort, and poison ivy. To better assess this annoying discovery, I carefully stepped closer and discovered several sprouts of poison sumac too! The red stems of the compound leaflet are an excellent identifying feature, which help distinguish it from other sumac species. Also, the large compound leaves have smooth edges unlike the serrated leaves of the more common staghorn sumac.
John Eastman, in his fascinating book Swamp and Bog, explains that the flaming red fall leaves are an example of foliar fruit flagging that makes the plant visible and attracts birds to eat the fruit and disperse the seeds. Or to attract nature students to pick the leaves and get an itchy poison sumac skin rash!!