Poison oak, or Toxicodendron diversilobum, is a plant found primarily in the western half of the United States, but also pops up in the eastern part as well. This diverse plant takes many forms and there are a number of plants that are confused for this pesky species. Prevent contact with poison oak by learning some of its many look-alikes. If you suspect you have come into contact with poison oak or develop an unidentified rash after handling an unknown plant, seek the advice of a licensed medical professional.
The red mulberry tree, Morus rubrus, and the white mulberry tree, Morus alba, are woody shrubs often mistaken for poison oak. The leaf structure of red and white mulberry is similar to that of poison oak, appearing with multi-lobed leaf margins that resemble the leaves of a true oak tree. The leaves of poison oak are shiny and dark green, whereas white and red mulberry trees have hairy, rough leaves that feel like sandpaper to the touch. Unlike poison oak, mulberry plants have polymorphic leaf structures. One branch may hold leaves that look entirely different from one another. Poison oak has the potential to grow as a woody vine and prefers wet to damp, shaded areas. Mulberry, on the other hand, prefers partial shade and damp to dry soil types.
Poison oak is a tricky plant. In addition to growing as a shrub or tree, it also grows as a vine. Poison oak in vine form looks similar to blackberry vines. Blackberry vines of the Rubus genus are marked with five to seven leaflets along their thick, woody vines, similar to the configuration of the poison oak plant. As the plant matures, the leaves of blackberry plants break off into clusters of five to seven, leading to further confusion of these plants with poison oak. Poison oak is extremely adaptable and possesses a number of different leaf shapes, adding to the difficulty of discerning whether a thicket of blackberry vines are truly blackberries or poison oak. Poison oak vines do not possess the same thorns or brambles that blackberry vines are known for.
Not all poison oak lookalikes are harmless. Poison ivy resembles poison oak in more than just a physical way. Both plants contain the chemical urishiol, which causes the notorious itching rash. Poison oak and poison ivy both have three to five leaflets, though the leaflets of poison ivy tend to be more triangular and serrated than its cousin poison oak. The colors of both plants can range from green to yellow to red. Poison ivy produces white berries and poison oak produces white, tan and green berries. Both should be avoided, if possible.
- Poison Ivy, Oak and Sumac Identification Center
- "A Field Guide to Poison Ivy, Poison Oak, and Poison Sumac: Prevention and Remedies"; Susan Carol Hauser, William L. Epstein; 2008
- Poison Ivy, Oak and Sumac ID Center: Is it Poison Ivy (or Oak)?
- Paddling.net: The Noxious Twins: Poison Ivy and Poison Oak