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.
A fibrous root system and stems that root where they come into contact with the
|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.
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 oak's leaflets have hairs on both surfaces
unlike those of poison ivy.