Download Poison Ivy (Toxicodendron radicans)

Poison Ivy (Toxicodendron radicans)
Synonyms: Rhus radicans, markweed, poison creeper, three-leaved ivy, picry, mercury
General description: A climbing or trailing, deciduous
woody vine with three leaflets, each about 10 cm long. Leaflet
margins are toothed, lobed, or entire; leaflets vary in shape
but often are egg-shaped. Leaflet stalks (petioles) are short
except on the middle leaflet. When growing as a climbing
vine, poison ivy attaches to trees or rocks by aerial roots. On
older plants, aerial roots give the stems a hairy, fibrous
appearance. Poison ivy is the major cause of allergenic
dermatitis in the eastern United States. All the parts of the
plant contain resinous compounds, known as urushiols, that
cause inflammation of the skin, blistering, and itching. About 50-60% of Americans are
sensitive to urushiols. The toxic compounds can be transmitted in smoke and by direct contact
with the plant or with objects or animals exposed to the plant, including tools, pets, and
clothing. The dermatitis response can occur year-round, even following contact with
overwintering stems and roots. Urushiols can remain active on objects and in dead plants for
over a year.
Propagation: Reproduces by seeds, creeping root stocks, and stems that root where they
contact the soil. Seeds are dispersed by birds.
Flowers and Fruit: Plants produce small yellowish green flowers on auxiliary panicles from
May to June. Greenish to grayish white berries (5 mm long) lack hairs and are produced in late
summer. They can persist on the plant throughout the winter.
Postsenescence Characteristics: In autumn, leaves often turn bright red, than drop by
midseason. Woody stems persist.
Habitat: Poison ivy can invade landscapes, disturbed sites, woodlands, and wetlands by
creeping stems or seeds deposited by birds. It thrives under a variety of conditions.
Distribution: Native and widespread throughout the midwestern, northern, and eastern
United States and parts of Canada.
Similar species: Poison oak (Toxicodendron toxicarium) is similar but
grows more erect, has blunt-tipped leaf apexes, and hairs on both surfaces of
the blade. Poison oak is only found from New Jersey southward. Virginia
creeper is similar, but has 5 leaflets per leaf and climbs by tendrils with
terminal adhesive disks.
From: Weeds of the Northeast, by Richard H. Uva, Joseph Neal, and Joseph DiTomaso, Cornell
University Press, Ithaca, NY, 1997.