Leaf:  Alternate, palmately compound, 3 leaflets; extremely variable, stiff and leathery or merely thin, somewhat hairy beneath or not, shiny or dull, coarse-toothed and wavy-edged, or neither; 7 to 10 inches long; end leaflet generally longer, pointed, and irregularly toothed, the side leaflets more mitten-shaped; long leafstalk, end leaflet with longer stalk than side leaflets, leafstalk often reddish at junction with stem; young leaves somewhat reddish-green; red autumn color.

Flower:  Small, greenish to yellowish, in racemes, 5 petals; blooming May to July.

Fruit:  Small, smooth, white or whitish-gray, ball-shaped, 1/4 inch (6 mm) in diameter, clustered loosely; green, turning white; persisting from August to November or longer.

Twig:  Brown and, if climbing, have many short aerial rootlets; buds visible, hairy, without scales, pinched at base; leaf scars large, with 6 or so bundle scars.

Bark:  Old stems of climbing vines densely covered with dark fibers and many aerial roots.

Form:  Erect shrub, trailing vine, or climber.
 

Discussion

Poison ivy is one of the important plant varieties consumed in winter by white-tailed deer.  The deer eat poison ivy leaves when available, and they consume the fruits from fall through spring.  A wide variety of migrant and resident birds also eat the fruits, including quail, pheasants, prairie chickens, and grouse.  Many seeds pass undamaged through their digestive systems, thus distributing poison ivy.  The flowers are visited by many kinds of insects, including honeybees.

Poison ivy sap has been used to make indelible ink.  Despite its dermatitis-causing properties, poison ivy is cultivated in some  gardens where it is valued for its red autumn foliage.  For 50 years, poison ivy has been planted to prevent dike erosion in the Netherlands.

Poison ivy rash is an allergic contact rash caused by contact with an oil called urushiol.  Urushiol is found in the sap of poison ivy, poison oak, and poison sumac.  It is a colorless or pale yellow oil that oozes from stems and leaves.  After exposure to air, urushiol turns brownish-black, makes it easier to spot.  Once urushiol touches the skin, it begins to penetrate in minutes.  In those who are sensitive, a reaction appears as a line or streak of rash, usually within 12 to 48 hours.  Redness and swelling occur, often followed by blisters severe itching.  In a few days, the blisters may become crusted and begin to scale.  

Ingested leaves do not confer immunity and can cause humans serious gastric disturbances.

Distinguishing Characteristics

Poison ivy and poison oak are the only common thornless alternate-leaved woody plants with 3-parted leaves and visible buds.  In winter, even the upright form can be distinguished by numerous bundle scars and stalked hairy buds.  The long stalks of the end leaflets and the white fruits are additional, though seasonal, field marks.  Poison ivy is the only alternate-leaved vine that climbs by aerial rootlets and the only one with fiber-hairy stems.  

Distribution

Poison-ivy occurs in all states east of the southern Cascades, Great Basin, and Mojave Desert.

Images

Click each small picture to see a larger image.

Upper surface June, 2003	Lower surface October, 2002 MG	Old bark on large specimen October, 2002 MG	Form and fall color, large specimen October, 2002 JW
	Fruits June, 2003	Fruits October, 2002 MG

Location

N 39.27775°  W -89.87848°
Northeast corner of East Second South Street and High Street, Carlinville, Macoupin County, IL.  

Copyright

Photos © 2002  Mark Goesmann, Carlinville High School, linke@carlinvilleschools.net
Photos © 2002  Jessica Williams,  Carlinville High School, linke@carlinvilleschoos.net

References

American Academy of Dermatology
http://www.aad.org/pamphlets/PoisonIvy.html

USDA Plant Database
http://www.fs.fed.us/database/feis/plants/vine/toxrad/value_and_use.html

George A. Petrides, Trees and Shrubs, 1986, Houghton Mifflin Company.

Margaret Meissner Evans, Green Heritage:  Vascular Flora of Macon County, Illinois, and Environs, 1990, Abbott and Foran, Inc.

USDA, "Pollen as Indicators of Source Areas and Foraging Resources"
http://pollen.usda.gov/Pollen_descriptions/Toxicodendron_radicans.htm

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