Toxicodendron radicans, more commonly known as poison ivy, does not have thorns. The most obvious physical characteristic of poison ivy, to help in detection and avoidance, is that the leaves grow in clusters of three.
The compound that causes irritation from poison ivy is contained in every part of the plant and is called urushoil. This long-lasting compound is stable enough to remain intact long after the plant has died. Urushoil is present in poison ivy, poison oak and poison sumac plants; to avoid the rashes associated with this compound, individuals should wash affected areas immediately after contact with the plant.