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| Poison Ivy | ||||||||||||||
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| Toxicodendron radicans |
Poison ivy grows vigorously throughout much of North America, but particularly in the American Midwest. It can grow as a shrub up to about four feet tall, or as a groundcover four to ten inches high, or as a climbing vine on any and every support. Older vines on substantial supports send out lateral branches that may at first be mistaken for tree limbs.
Poison ivy is apparently far more common now than when the Europeans first entered North America, because it has profited immensely from the " edge effect", enabling it to form lush colonies in such places.
The leaves are compound with three leaflets, giving rise to the doggerel, "Leaflets three, let it be." The berries (actually drupes) are a grayish-white color and are a favorite winter food of some birds.
Poison ivy looks like ivy. Each tendril of ivy ends in three leaves which are almond shaped. Color ranges from light green (usually the younger leaves) to dark green (mature leaves). Leaves can be as long as 10 or 12 inches long, but are usually 4-6 inches long when they are mature. Each leaf has a FEW teeth along its edge, and the leaf surface is SMOOTH. To compare, blackberry and raspberry leaves also come in threes, but they have MANY teeth along the leaf edge, and the top surface of their leaves are very wrinkled where the veins are. The stem and vine are smooth, brown and woody, while blackberry stems are green with thorns.
Virginia creeper, Parthenocissus quinquefolia, vine can look like poison ivy. The younger leaves can come in groups of three but have a few more serrations along the leaf edge, and the leaf surface is somewhat wrinkled. Virginia creeper and poison ivy very often grow together, even on the same tree. Poison oakPoison oak : Plantae : Magnoliophyta : Magnoliopsida : Sapindales : Anacardiaceae : Toxicodendron Diversilobum Binomial name Toxicodendron diversilobum Western poison oak Toxicodendron diversilobum or, previously, Rhus diversiloba is found only on the Pac leaves also come in threes on the end of a stem, but each leaf is shaped somewhat like an oak leaf. True poison oak only grows in the western United States, although many people will refer to poison ivy as poison oak. This is because poison ivy will grow in either the ivy-like form or the brushy oak-like form depending on the moisture and brightness of its environment. The ivy form likes shady areas with only a little sun, and tends to climb the trunks of trees, and can spread rapidly along the ground.If the poison ivy is growing up a tree look at the vine. It will be smooth with no ladder like roots clinging to the tree. (Some sources report that poison ivy does have these ladder like roots.)
Beware of dead poison ivy: it still has plenty of urushiol, and will give the same effect. Compare the thick vines of grape: no rootlets visible, to the vines of poison ivy: so many rootlets that the stem going up a tree looks furry.
The skin rash, featuring fluid-filled blisterA blister is a defense mechanism of the human body. It consists of a pool of lymph and other bodily fluids beneath the upper layers of the skin. It may be formed in response to burns or friction, and helps to repair damage to the skin. If a blister is puns and reddened areas that itch intensely, is caused by an irritating oilOil is a generic term for fluids that are not miscible with water. The name comes from Latin oleum for olive oil. Oil is frequently used to refer to petroleum an "oil shortage" generally means an inadequate supply of petroleum rather than cooking oil., urushiol. Urushiol binds to skin cell membranes, changing their configuration, so that the body's immune system no longer recognizes these cells as belonging to the body and attacks them as foreign. Some people are susceptible to the rash, and others aren't, but reactions can change during a person's lifetime. Someone who was formerly not subject to it may become very sensitive, and vice versa.
Normally, it takes about twenty-four hours for the rash to first appear, though it may worsen during the next few days and may appear to spread, when in fact what is happening is that areas that received a lesser dose are latently reacting. The rash takes one to two weeks to run its course, but normally does not leave scars. Severe cases will have small (1-2mm) white fluid-filled blisters on the skin.
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