Poison Ivy

Toxicodendron radicans

Weed Description
A woody vine that may occur as a weed of landscapes, woods, fencerows, pastures, and hay fields. Poison ivy is the major cause of allergenic dermatitis in the eastern United States, which causes inflammation, blistering, and itching of the skin. The plant sap contains a chemical called urushiol, which is found within ducts in the leaves, flowers, stems, and roots of this weed. When poison ivy plants are bruised or damaged, this chemical is emitted onto the leaf and stem surfaces where humans and animals may come into contact with it. Poison ivy is found throughout the southern United States east of the Mississippi River. It also occurs more sporadically in the midwestern and northern United States.

Leaves
Leaves occur on petioles and are divided into 3 leaflets which are generally oval in outline. Leaflets may be either toothed, untoothed, or lobed. Older leaves are generally either toothed and lobed or untoothed and lobed. The two lateral leaflets occur on very short petioles, while the central leaflet occurs on a much longer petiole. Although leaf shape is highly variable, the lateral leaflets are often distinctly lobed on one side of the leaflet and not on the other. Each leaflet is hairless and ranges from 3/4 to 4 inches in length and width.

Stems
Woody, climbing on other vegetation or objects or trailing along the ground. When climbing, poison ivy attaches to other objects by way of aerial roots. Stems are capable of rooting when they come into contact with the soil.

Flowers
Flowers are small and inconspicuous, yellowish green to green in color. Flowers occur in clusters of 2 to 6 on stalks that arise from the position between the leaf petioles and stems (leaf axils).

Fruit
A berry, gray to white in color, approximately 5 mm wide.

Roots
A fibrous root system and stems that root where they come into contact with the ground.

Identifying Characteristics
The climbing or trailing nature of this weed, woody growth habit, and irregularly lobed and toothed leaflets are all characteristics that help in the identification of poison ivy. Virginia Creeper (Parthenocissus quinquefolia) is often mistakenly identified as poison ivy, however this weed has leaves that are divided into 5 leaflets while poison ivy has leaves that are divided into 3 leaflets. Poison Oak (Toxicodendron toxicarium) is very similar to poison ivy, however poison oak has much duller green leaves that are usually more distinctly lobed or toothed. Additionally, poison oaks leaflets have hairs on both surfaces unlike those of poison ivy.

Office of Programs

University of Missouri

Poison Ivy

Toxicodendron radicans