Poison Ivy

Say one thing about poison ivy, it's extremely adaptable. It grows up north; it grows down south. It thrives in the sun; it thrives in the shade. It grows as a shrub six feet tall, or a vine 150 feet long, up a tree or along the ground.

And every inch of it skin-irritating, because of urushiol, the same oil found in poison oak, poison sumac and poisonwood.

The leaves of poison ivy are irregular — their shapes can differ even on the same plant. But poison ivy always has three leaflets, the middle one on a stem longer than the first two. Leaflets of three, let it be. It's the one plant anyone who wanders in the woods has to know.

Poison ivy has clusters of nondescript greenish-white flowers that produce a white, waxy berry-like fruit. Birds eat them — it's actually an important source of food for some species — and the plant, leaves and all, is food for deer.

For us human types, the practical benefits of poison ivy are pretty much limited to — nothing. It's been used in folk medicine to treat osteoarthritis, but studies haven't confirmed its usefulness. It's also been used to try to desensitize patients with urushiol allergies, but that's been discredited. It's also been used as a folk remedy for liver ailments. We've read that some eat small quantities of the leaves in order to build immunity to urushiol, but medical experts say taking poison ivy internally is a very bad idea.

Some people mistake Virginia creeper for poison ivy, but the resemblance really isn't close. Virginia creeper has five leaflets, and tendrils, which poison ivy lacks. Poison ivy's scientific name: Toxicodendron radicans.

Urushiol is so potent that a single nanogram of the oil is enough to cause a rash to break out on a human, according to the Poison Ivy, Oak, Sumac Information Center. A quarter-ounce is enough to give everyone on the planet a rash. It can remain active on a surface for as long as five years, even on a dead plant.

Oddly enough, people with certain immune deficiencies, including AIDS, are less likely to develop a rash from exposure to urushiol. On the other hand, reactions can be severe for those who are allergic to the oil — blisters can break out on the skin and eyes can swell shut. Soap and water can remove urushiol, like most other oils. However, urushiol tends to seep deep into the skin and bond in three to 30 minutes.

Back to the plant itself: It is a pioneer species, meaning it will be among the first species to make a home in a newly cleared area, from a fire, death of a tree or other disturbance. Poison ivy produces clusters of berries that turn white when ripen, seen in the first photo below, but they are nutritionally low quality. Up north in the fall, migrating birds will munch on better quality fruit, largely ignoring poison ivy. That leaves them available, and especially valuable, to species that winter over. All in all, 60 species of birds eat poison ivy.

Fun fact No. 1: Captain John Smith of Jamestown and Pocahontas fame coined the name, poison ivy. Smith also gave us opossum.

Fun Fact No. 2: Minnesota has declared poison ivy to be a prohibited noxious weed. No kidding.

Fun Fact No. 3: Urushiol comes from a Japanese word meaning lacquer. When workers restored the gold leaf on Kinkaku-ji (Temple of the Golden Pavilion) in Kyoto in 1987, they used urushiol lacquer to preserve and maintain the gold. Yes, any thieves would have been caught red-handed.

Fun fact No. 4: What grows in Florida and most of North America Texas eastward is called eastern poison ivy (also spelled poison-ivy). There is a western poison ivy, Toxicodendron rydbergii, found over much of the continent, including the Mid-Atlantic states and the Northeast. But not here. Thankfully.

Poison ivy is a member of Anacardiacae, the sumac family, which also includes mangoes, cashews and pistachios.