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Wild Parsnip: Invasive Plant That "Burns"

Arkansas Natural Heritage Commission - Thursday, July 21, 2016

Theo Witsell, ANHC botanist and ecologist, was recently interviewed by THV 11 and featured on an evening news cast that focused on wild parsnip (Pastinaca sativa), an invasive plant. A woman in northwest Arkansas recently encountered the plant, leading many to think the plant is spreading throughout the state.

Wild parsnip is said to resemble Queen Anne’s-lace (Daucus carota), another non-native invasive plant that is widespread in Arkansas. Much like Queen Anne’s-lace, wild parsnip grows along roadsides, in abandoned fields, pastures, and open areas. Despite recent media attention, wild parsnip is primarily a problem for states north of Arkansas.

Even though wild parsnip isn’t common in Arkansas, it has garnered attention because of the painful skin irritation that can come from encountering it. Chemicals in the plant’s sap, called furocoumarins, cause an inflammatory skin reaction when they are exposed to sunlight (ultraviolet light or UV light). The condition is called phytophotodermatitis and unlike an immune response, can occur in anyone who has been exposed to the chemical and sunlight, whether or not he or she has been exposed to the plant chemicals previously.

Why is sunlight needed to cause the skin reaction? The furocoumarins are absorbed by the skin and activated by the UV light, causing them to bind with nuclear DNA and cell membranes. This destroys the cells and skin tissue, though the reaction isn’t immediately noticeable. In mild cases, the inflammatory response resembles sunburn. In more severe cases, blisters appear within a few days of exposure and it is said to feel like the skin has been scalded. Perspiration and heat speed up the body’s absorption of the furocoumarins and exposed sensitive areas are affected most severely.

The skin’s reaction to wild parsnip is often misdiagnosed as exposure to poison ivy, oak, or sumac. However, there are some distinct differences. The inflammatory response occurs only on skin that has been exposed to sunlight. Exposure to the plant chemicals and UV light also cause streaks and long spots along the skin, due to hyperpigmentation (dark discoloration). The hyperpigmentation can appear up to two weeks later and can last for months to years, with some people reporting that they have remained hypersensitive to UV light for years (Source: telemedicine.org/botanica/bot5.htm).

Do we know why plants produce furocoumarins? It is believed that the chemicals are used to defend the plant from fungal attack, rather than from contact with people or other animals. An increase in these chemicals has been documented in other plants, like celery, when the plant is fighting off a fungal infection.

Wild parsnip has only been collected from the state in two counties, Benton and Jefferson. We know this from consulting the “Atlas of the Vascular Plants of Arkansas”, a comprehensive accounting of the wild plants of Arkansas published by the Arkansas Vascular Flora Committee. Each species is presented along with a county-level distribution map showing where it has been “vouchered” (officially documented by the collection of a pressed and dried herbarium specimen). These maps are the result of nearly 200 years of collecting by hundreds of professional and amateur botanists. You can learn more about the “Atlas” in our June 2014 enews article.

 

Photos

Above right: Theo Witsell during THV 11 interview about wild parsnip.

Above left: Wild parsnip, photo by Rob Routledge, Sault College, bugwood.org

Right: cover of the "Atlas of the Vascular Plants of Arkansas"

 

 

 

 

 

 

 

 



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