Toxicodendron Toxicity

Excerpt

Toxicodendron is a genus of plants, shrubs, vines, and trees within the Anacardiaceae family. Common names of plants within the family include poison oak, poison ivy, poison sumac, and the Chinese lacquer tree. Many of these names come from similar appearances to other leaves that are non-toxic. The genus as a whole is widespread throughout North America except for Hawaii and Alaska and can have regional variations in appearance. Many of these plants prefer lower elevations and are typically found below 1500 meters. An often-repeated adage regarding their identification is “leaves of three, leave it be,” but it should not be the sole method used. Poison ivy is pervasive throughout North America and has been known to hybridize where its geographic distribution overlaps. Eastern poison ivy (Toxicodendron radicans) is commonly found in the eastern half of North America and typically appears as a vine with almond-shaped leaves in groups of three. Leaves change from green to red in the fall. Western or Rydberg’s poison ivy (Toxicodendron rydbergii) is commonly found as a shrub with small yellow berries. It is distributed throughout much of North America, with the general exception of the Southeastern United States.

All parts of both plants contain urushiol, which causes characteristic dermatitis associated with exposure. While the genus and its many subspecies have a strong predilection for North America, they can both be found in China, Mexico, Africa, Australia, and New Zealand, to name a few other places. Poison oak has two common variations. Western poison oak (Toxicodendron diversilobum) is a deciduous shrub with scalloped or lobed leaves, generally appearing in groups of three that resemble true oak leaves. It is found primarily west of the Rocky Mountains, as the name suggests. While Eastern or Atlantic poison oak (Toxicodendron pubescens or quercifolium) is frequently confused with Eastern poison ivy as it has three grouped leaves that are structurally similar in appearance. A unique feature useful in identification is the presence of clustered small green fuzzy berries on the plant. Distribution is more common in the Southeastern United States but can extend as far north as New Jersey. The leaves of both western and Atlantic poison oak change colors in the fall time and drop off in the Western species. Poison sumac (Toxicodendron vernix) is a deciduous tree or tall shrub found in moist, swampy areas of the eastern United States. It has red stems with a pinnate or feather-like leaf arrangement comprised of 7 to 13 oblong or oval-shaped leaves. The plant also produces green clustering flowers and small globular fruit. The leaves and fruit of the plant are the primary sources of urushiol.

The Chinese lacquer tree (Toxicodendron vernicifluum) is a common deciduous tree in many Asian countries and gets its name for the use of its urushiol-containing sap in lacquer production. Leaves are large and grouped in leaflets of 7 to 19 with flowers that bloom in the summer. All parts of Toxicodendron plants contain urushiol, which is found in sap channeled within the plant. When exposed to air, urushiol turns black and hardens to prevent moisture loss and can be useful in identifying plants in the fall. Urushiol is the primary allergenic cause of contact dermatitis and is typically encountered by brushing up against damaged stems or leaves. Skin exposure results in rapid absorption of the urushiol due to its lipophilic nature. Names for the toxicity are variable and include names such as Rhus dermatitis, urushiol-induced contact dermatitis, and Toxicodendron dermatitis.