Along with its relatives poison ivy (Toxicodendron radicans) and Pacific poison oak (Toxicodendron diversilobum), Poison sumac (Toxicodendronvernix) is one of the most notorious plants on Earth. Growing as a shrub or small tree, poison sumac can reach 20 feet in height, although they are usually somewhat smaller.
Poison sumac leaves are pinnately compound (feather-like) and arranged alternately on the branch. The leaflets have smooth margins and typically number 7 or 9, but occasional specimens may produce leaves with 11, 13 or 15 leaflets. The central stem of the leaflet – called the rachis – is red on young leaves and gray to brown on older leaves.
Like the other members of the genus Toxicodendron, poison sumac contains the potent allergen urushiol. Found throughout all of the plant’s tissues, the oil can cause a severe, itchy rash in humans who contact the plant. Rashes can result from contact with minute quantities of the oil, which can also be carried on clothing that has brushed against the plant. Even leaves that have been thoroughly dried remain potent.
Perhaps the greatest danger occurs when the plant is burned. This produces a thick, urushiol-laden smoke, which can wreak horrific damage on the lungs of any who breathe it. Many authorities claim that, by virtue of small differences in its chemical composition, urushiol from poison sumacs is more allergenic than that from poison ivy and poison oak.
Identifying Poison Sumac
Unlike poison ivy and poison oak, which are easy to identify by noting their “leaves of three,” poison sumac is a bit more difficult to identify in the landscape. You can look for the alternating, compound leaves bearing 7 to 9 leaflets. However, trouble ensues when people mistakenly observe the leaflets, which are arranged on opposite sides of the rachis, when they think they are observing the leaves – which are arranged alternately around the stem.
Accordingly, it is wise to consider other factors as well. For example, poison sumac tends to grow in very damp, acidic habitats (sometimes the roots actually grow into standing water). However, this is not a foolproof criterion – many ash trees (Fraxinus spp.) and true sumacs (Rhus spp.) grow in similar habitats and have compound leaves.
However, poison sumac produces round, waxy, white to yellow berries. By observing the combination of alternately arranged leaves and white berries, you can rule out most other species. Just remember the phrase: Berries of white make for a dangerous sight.
The berries of poison sumac trees typically persist well into the winter, hanging around long after the deciduous leaves have turned red and fallen to the forest floor. Accordingly, poison sumac is often an important food source for winter wildlife. Strangely, few animals (if any) appear to be allergic to urushiol.
Rabbits, squirrels, chipmunks, rats, mice and other small mammals are some of the most important consumers of the berries, and it is possible that many other mammals feed on them from time to time. Despite being most common in low-lying habitats, poison sumac berries appear to be relished by several upland game bird species, including bobwhites, pheasants and grouse.