Poison Ivy

 

Poison Ivy (Toxicodendron radicans) leaf in the fall.  
Rowan County, North Carolina.

Poison Ivy (Toxicodendron radicans) is both a plant and an idea. Its genus, Toxicodendron mean poison tree.  This name is very apt because Poison Ivy causes severe contact dermatitis and is the leading cause of allergic reaction in the United States.  The medical aspect of this plant’s life inspired a hit song by the Coasters in the 1950s and the song led to an anti-heroine named Poison Ivy in the Batman universe from the 1960s to today. 

 

Poison Ivy leaf in summer with its three leaflets
and serrations.  Rowan County, North Carolina.

Poison Ivy is in the family Anacardiaceae, a group of plants that includes; Poison Sumac, Poison Oak, Mango and Cashew.   It grows throughout Eastern North American from Texas to Canada.  The toxic nature of the plant has spawned some nursery rhymes so children could avoid it in the field.  These include; “Leaves of three, let it be” and “Hairy vine, no friend of mine”. 

 

The hairy vine of Poison Ivy in winter.  The hairs are actually
fine roots that fix the vine to the tree trunk. 
Clayton County, Georgia.

As the rhyme says, Poison Ivy is a vine.  It can sprawl across the ground or grow up trees.  The vine is not actually hairy, but rather covered with short roots that attach it to the tree trunk. The specific epithet in the scientific name, T. radicans, refers to these roots.  The other rhyme mentions leaves of three.  These are really three leaflets of a single compound leaf and the margins of the leaflets often have teeth.  In the spring, the leaves are shiny and plant makes small, inconspicuous, green flowers. As summer progresses the leaves lose their luster and green fruits develop from the flowers.  Birds, who suffer no ill effects from the poison, greedily eat the fruits.  Poison Ivy leaves turn a brilliant yellow and red in the fall. 

Early spring leaves of Poison Ivy. The young leaves start out red then turn green.
Rowan County, North Carolina.

 

Spring leaves and flowers of Poison Ivy.
The pale green flowers are borne in the leaf axils. 
Rowan County, North Carolina.

Poison Ivy fruits in late summer.
Rowan County, North Carolina.

Southeastern Poison Oak (Toxicodendron pubescens) is very similar to Poison Ivy in appearance, growth habit and toxicity.  A key difference between these species is the leaves of Southeastern Poison Oak are lobed, like those of oaks rather than toothed. 

 

Poison Oak (Toxicodendron pubescens) with fruit.
Rowan County, North Carolina. 

The poison in Poison Ivy is a compound called urushiol.  This oily mix of molecules is made in all parts of the plant so roots, stems, leaves, flower and fruits can all cause dermatitis.  It is possible to remove the oils from skin with immediate washing with soap and water.  But often, you don’t know you have come brushed up against the plant.  Upon contact with skin, the urushiol attaches to a protein on the surface of immune cells.  The combination of the urushiol and the cell protein cause an exaggerated allergic response.   A couple of days after someone comes in contact with Poison Ivy, they experience itching and angry red welts that fill with fluid.  A poison ivy rash often spreads.  The spreading rash is due in part to the initial immune cell stimulating other cells to produce inflammatory molecules.  Poison Ivy rash may last for a week or more.  Exposure to smoke of burning Poison Ivy plants is more dangerous. Inhaling the smoke can cause severe inflammation of the lungs and even death.  Treatments for a Poison Ivy induced dermatitis range from the traditional oatmeal bath to Calamine lotion to prescription steroids. 

 

Contact dermatitis caused by Poison Ivy.
Rowan County, North Carolina.

About 80% of the population is susceptible to the toxic oils in Poison Ivy.  I break out in a rash when I brush up against this plant and always try to avoid it. Even in winter, I stay away from the hairy vine that is no friend of mine.