Tips to Identify Poison Ivy

POISON IVY (Toxicodendron radicans)

WESTERN POISON IVY (Toxicodendron rydbergii)

Poison ivy belongs to the family Anacardiaceae (the Sumac family). It grows primarily in temperate climates in the Americas and Asia. There are about 30 species, and the majority are Asian. Some authors include Toxicondendron in the genus Rhus (Sumac), and you may see the scientific name written Rhus radicans

LEAF TYPE:

• Compound leaves with three leaflets (leading to the saying "leaves of three, let it be")
• The stalk of the middle leaflet is much longer than the stalks of the two side leaflets
• The edges can be smooth or coarsely toothed
• Surface can be glossy or dull

LEAF ARRANGEMENT:

• Alternate

GROWTH FORM:

• Climbing or straggling vine (poison ivy)
• Sprawling shrub (western poison ivy)

FLOWERS:

• Inconspicuous greenish flowers with five petals, about 3 mm in diameter
• Flowers in loose branching clusters arising from the leaf axil (where the branch or leaf attaches to the stem)

FRUITS:

• Fruits in loose drooping clusters
• Berry-like fruits containing a single seed (drupes) are hard and whitish

RELATIVES:

• Poison oak (Toxicodendron pubescens) is a low shrub bearing compound leaves with three leaflets, but the leaflet edges have rounded lobes and resemble oak leaves. The young twigs, petioles, and sometimes the leaves are covered with hairs.
• Poison sumac (Toxicodendron vernix) is a tall shrub (to 5 meters) usually found in swamps. The leaves are (compound), odd pinnate. The 7-13 leaflets have smooth edges and pointed tips.
• Some well-known tropical relatives are mango (Mangifera indica) and cashew nut (Anacardium occidentale).

Poison ivy is number one on our list of plants to avoid, because it contains a resin that can induce a very unpleasant skin rash if you touch it. Most plants have some sort of chemical defense system that helps protect them against predators, and the chemicals produced by poison ivy and its relatives are particularly effective. The resin contains a mixture of compounds that can bind to skin proteins upon direct contact. These complexes are then recognized by the human immune system (T-cells), resulting in a hypersensitivity reaction. The reaction, characterized by skin eruptions that itch and burn, can develop 12 hours to 5 days after exposure. Most people do not experience skin rashes the first time they touch poison ivy, but subsequent contact can trigger the reaction. Other lucky people do not seem to be susceptible, even after repeated exposures.

There is one trick you can try right in the field if you think someone has touched poison ivy. See if you can find some jewelweed (touch-me-not, Impatiens spp.) growing in the area. Jewelweed has a very succulent stem, and the sap is reputed to be an effective remedy for poison ivy. It has a soothing effect on mosquito bites, too! Break off a stem, and rub the sap on the affected area. When you return to the classroom, anyone that even thinks they might have touched poison ivy should wash thoroughly with soap and water. Any clothes that have been in direct contact with poison ivy should be carefully removed and laundered, because you can even get dermatitis from touching a bit of resin picked up on clothes! The unpleasant itching of poison ivy can be relieved by applying calamine lotion or a paste made of baking soda. In the case of a severe reaction, or if the dermatitis affects a particularly sensitive area (face or eyes), a visit to the doctor is in order.

The best remedy is, of course, prevention. Learn to recognize and avoid poison ivy.