The Carlisle Mosquito Online

Friday, June 13, 2003


Poison ivy

Poison Ivy (left) is a similar size to a bramble (right) and both grow in the same habitat. (Photo by Kay Fairweather)
"Well late at night when you're sleeping, poison ivy comes a creeping all around." (Jerry Lieber/Mike Stoller)

It's Friday the thirteenth and I have chosen an infamous native plant. Most of us are unlucky enough to have the poison ivy allergy; it is the most common allergy in the country.

Name, family and relations: Toxicodendron radicans, previously classified as Rhus radicans. The name, poison ivy, was first used by Captain John Smith in 1609. Poison ivy is not an ivy, and poison oak is not an oak. They are both in the Cashew or Sumac family along with poison sumac. These toxic family members are now classified in the genus Toxicodendron while the non-toxic members are classified as Rhus. Non-toxic family members include cashews, pistachios and mangos. (It is possible to get a mild irritation from mangos, at the corners of your mouth, from freshly cut mango skin.)

When and where seen:. Poison ivy is all around town. It grows in both sun (like the open Towle Field) and shade (like the woods and partially shaded roadsides). It grows along the ground and up trees.

Description: Poison ivy is a plant that is worthwhile learning to identify · in all seasons. "Leaflets three, let it be" is a slogan for the better-safe-than-sorry crowd. Other plants with leaves in a look-alike arrangement are Jack-in-the-Pulpits, blackberries, raspberries, Virginia creeper, and wild sarsaparilla. The three leaves of poison ivy are two to four inches long and usually have wavy or jagged edges. When the leaves first appear they have a reddish tinge, then become green (not always shiny) and finally turn red in the fall. The flowers are small, off-white and inconspicuous and develop into clusters of round, waxy, whitish fruit that persist into winter if not eaten by birds. Poison ivy is a long-lived perennial. The stems of older climbing plants are woody, brown and very hairy and can reach up to five inches in diameter.

Urushiol: All parts of the plant, except the pollen, contain urushiol (pronounced you-ROO-she-ol) which is not toxic itself. It is absorbed into the skin and metabolized. The resulting metabolites bond with skin proteins and are then attacked by the body's immune system. The immune response is what causes the blistering and inflammation. The good news in this scenario is that if you wash off the urushiol before it is absorbed, no reaction will occur. Most sources recommend washing it off with cold water · no soap. Urushiol is very potent · a nanogram or one billionth of a gram can cause a rash. It is also a very stable compound and stays active for years after the plant is dead, and active on your clothes and shoes if not washed off.

Banishing the bad luck: Several methods are recommended for controlling poison ivy. You can spray it with a herbicide; you can rent a flock of sheep to eat it (goats will also eat it); you can cover it with a deep layer of mulch to prevent the light from reaching it; or you can pull it up. For small amounts, I prefer the pull-it-up method. Anyone with a dog can tell you that with a sturdy plastic bag on your hand you can safely pick up things you normally wouldn't touch. For the big woody vines growing up trees, you can sever the vine, carefully, and paint herbicide on to the freshly cut surface.

Very bad luck: If you burn poison ivy, the urushiol is carried in the smoke and can then be inhaled and also deposited all over your face, other exposed skin and clothing. Under no circumstances should you burn it.

Sources: Joan Raysor Darlington, Is It Poison Ivy;;

Submissions for the Biodiversity Corner are encouraged from anyone so moved. The column has featured insects, birds, mammals, trees, wildflowers, ferns, fungi, amphibians, reptiles and a liverwort. Be the first to do a fish! With all the rain lately this may now be easy. Send a note to Kay Fairweather at 392 School Street, Carlisle MA 01741 or to

2003 The Carlisle Mosquito