Poison ivy (Toxicodendron radicans) is robust, shade-tolerant, and manifests in multiple distinct growth-patterns. It's found almost everywhere in the Eastern woodlands and offers food for birds with its berries, although it can also spread asexually. These traits make it an important and resilient plant species, adding to its reputation as a fearsome nuisance.
The most salient aspect of poison ivy is the resin found in its leaves: urushiol. This term derives from the Japanese name for a related species, Toxicodendron vernicifluum, the Chinese lacquer tree. Not confined to poison ivy, urushiol resin can be found in many members of the family Anacardiaceae, which also contains the sumacs (genus Rhus) and the cashews (genus Anacardium). Despite its traditional use in East Asian arts and crafts as the primary ingredient for lacquerware decoration in woodworking, urushiol is a potentially dangerous poison. Contact with the resin leads to an immune-response whereby the skin is attacked by the afflicted's own T-cells. Rash, blisters, scarring, and even necrosis in severe cases results, and a prolonged healing period is generally required before the affected skin returns to normal.
Thankfully, not everyone experiences an allergic reaction after exposure. Even within nuclear families, one member will be allergic and another may be immune or only slightly allergic. For those who do "take poison ivy rash," knowing how to identify this plant is extremely important if you like to be outside. This plant isn't just found in the woods; it grows readily in town, and it frequently germinates in the arboretum as a volunteer; thanks, birds. Although it isn't welcome in the landscape, we never get rid of all of it.
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This is one of the arboretum's less-cultivated areas. It's a small wedge-shaped zone located near the southwest corner of Mickle Hall. Due to a serious problem of erosion in this section, we have allowed some extra undergrowth to accumulate that would not be tolerated elsewhere. Over the last approximately three years it has only been mowed once.
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A couple of poison ivy plants were spotted this week. Two vines were growing straight up, and they had grown taller than the surrounding plants, making themselves conspicuous. The Japanese proverb Derukui Wautareru (The nail that stands up gets hammered down) is appropriate here, given the urushiol. Let the rest of the arboretum's denizens be thus warned.
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This is the tallest vine that was snipped. Several additional pieces were carefully cut, photographed and then discarded.
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This is a detail image of the vine. Here we see light green leaf stems alternating along a light-brown vine.
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Poison ivy has compound leaves. In this photo, we see one leaf. Each leaf has three leaflets. Some people find the saying "Leaves of three, let it be" helpful; other people find such expressions confusing.
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This is another leaf. There are three leaflets, and one leaflet shows signs of predation. Who out there is bold enough to chow down on poison ivy?
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USDA page on Poison Ivy
LSUAgCenter page on Poison Ivy ID
Urushiol and lacquerware
