A couple of years ago, I was introduced to wild parsnip (Pastinaca sativa). It was growing in the ditch, and I was reaching for it when four family members screamed, “Don’t touch! Get back.” The plant looked harmless, like a wild carrot; but I learned that day about one more plant to add to my “don’t touch” list.

Wild parsnip, or poison parsnip, is not really poisonous; however, it can cause sun-induced blistering or “burns” on the skin. The sap contains chemicals, furocoumarins, that cause phytophotodermatitis. Basically, if your skin absorbs these chemicals and is then exposed to sunlight, an interaction takes place; the result is reddened, burned-like skin and/or blisters. For more information on diagnosing this reaction, check out David J. Eagan’s article, “Burned by wild parsnip,” Wisconsin Natural Resources Magazine, at www.wnrmag.com/stories/1999/jun99/parsnip.htm.

I now know that wild parsnip can be quickly distinguished from many of its weedy cousins by its yellow flowers. Also, the leaves are pinnately compound, divided once into more than five leaflets with coarsely sawtoothed edges, and they are hairless.

Wild carrot (Daucus carota), or Queen Anne’s lace, has leaves that are many times pinnately compound, finely dissected, and hairy. It also has umbel flowers, but the petals are white not yellow. You can fill vases with the pretty, lacelike flowers and most likely remain blister free; but resist the urge to plant this plant in your garden, as it spreads rampantly.

Poison-hemlock (Conium maculatum) is a similar, related species. This time, the name is accurate as the entire plant is very poisonous, containing toxic alkaloids that cause respiratory failure when ingested. Also reported are birth defects in livestock. Fortunately, this plant should leave you blisterfree. Like wild carrot, the flowers are white but smaller, only 1.5 to 2.5 inches compared to 3 to 6.5 inches. The leaves of wild carrot have a carrot scent. Likewise, wild parsnip smells like a parsnip. A crushed poison-hemlock plant smells unpleasant. It has smooth, purple spotted, ridged stems that are hollow between the nodes. Wild carrot stems are quite different: bristly hairy, vertically ribbed, purple-spot-free, and not hollow. Wild parsnip stems are usually somewhat hairy and grooved. Stem size makes up for the smaller flowers; poison-hemlock grows erect, 2 to 7 feet tall, while wild carrot usually reaches 1 to 3 feet. Wild parsnip falls in the middle at 2 to 5 feet tall.

These three plants are all biennial weeds commonly found in roadsides, waste areas, pastures, meadows, and even landscapes. Each begins as a rosette, bolts in the second year, and produces many seeds. The under ground portion consists of a fleshy taproot.

A few more distant cousins. Another member of the Umbelliferae family, spotted waterhemlock (Cicuta maculata), is often confused with wild carrot and poison-hemlock. This plant, however, has a cluster of fleshy taproots at its base. It is a perennial mainly found in wetter areas; all parts are poisonous if eaten.

Cow parsnip (Heracleum maximum or H. lanatum) is a biennial that occurs in 55 Illinois counties but is common only north of I-80. It too tends to be found in wetter areas. This plant reportedly causes dermatitis in humans; cattle can be poisoned by eating the leaves--which are enormous, up to 16 inches long and 12 inches wide! Fortunately, it’s not considered to be very invasive or weedy.

Precautions. A good weed ID book can be beneficial. While hand-pulling or working around plants that cause skin conditions, it’s advisable to wear long pants, long sleeves, and gloves. Working after sunset can help prevent blistering and burns, too. Mowing can reduce seed production. Applying herbicide to the rosette in the early fall or late spring can control many in this family. Repeat applications may be necessary. Suggested options include 2,4-D, dicamba, MCPP, MCPA, or metsulfuron. Spot treatments of glyphosate can be effective as well. As always, carefully read and follow all label directions.