This article was written by guest author Tom Scavo, a new Vermonter, published author, and experienced educator, now semi-retired.
Wild parsnip was in the news recently (July 2018) when a Vermont woman posted photos of her horribly blistered leg. Click on that link to see for yourself the damage this plant can cause.
Wild parsnip is a member of the Apiaceae family, also known as the Umbelliferae, commonly called the carrot (or parsley) family. Wikipedia claims there are 3700 species in this family of herbaceous plants, including numerous domesticated root vegetables such as carrot, parsnip, celery, and parsley, as well as many wild species.
The Apiaceae family consists of mostly flowering plants, with white, yellow, pink, or purple flowers. The flower arrangement is characteristically umbrella-shaped (called an umbel); hence the alternative family name Umbelliferae (which is easier to pronounce and remember). Hereafter we refer to a member of this family as an umbellifer (think: umbrella).
This article surveys a representative sample of umbellifers but first, I give a brief summary of the most important facts.
There are basically two things you need to know about the Apiaceae (carrot) family of plants:
- Numerous species in the carrot family of plants can cause phytophotodermatitis, an unpleasant skin condition. If you come in contact with the sap of one of these plants (such as the wild parsnip), immediately wash the affected area and avoid any further exposure to sunlight.
- Some species of the carrot family are poisonous—do not gather roots, herbs, or seeds in the fields or woods unless you know what you’re doing.
As a rule of thumb, treat the umbellifers as you do the mushrooms: Admire their natural beauty and diversity but maintain your distance.
The carrot family is not the only family of plants with phototoxic species and/or poisonous species so the previous advice is generally applicable. See the last section for tips on how to prevent phytophotodermatitis.
Apiaceae Family Survey
While some umbellifers are important crop plants, others are noxious, some are invasive, and a few are highly poisonous. Here is a representative sample of various species in the carrot family:
- Cow parsnip (Heracleum maximum)
- Queen Anne’s lace (Daucus carota)
- Wild parsnip (Pastinaca sativa)
- Giant hogweed (Heracleum mantegazzianum)
- Poison hemlock (Conium maculatum)
- Spotted water hemlock (Cicuta maculata)
The U.S. Fish and Wildlife Service characterizes the above species as six lookalikes you want to avoid. Why? Because each of these plants produces a sap containing a chemical compound (called furanocoumarin) that sensitizes human skin to sunlight. Contact with the plant sap may cause phytophotodermatitis (which is what happened to the Vermont woman mentioned earlier) but a reaction can be averted simply by washing the affected area and avoiding exposure to sunlight.
Not all species in the Apiaceae family are equally dangerous. The above species are listed in increasing order of (perceived) danger. Apparently, three of the species are even more dangerous than wild parsnip! Indeed, the hemlocks are highly poisonous, and in some cases, deadly.
In practice, however, it is difficult to distinguish the good from the bad. Wild parsnip is the only species listed that has yellow flowers, so it is relatively easy to identify a mature plant. All the rest have white flowers and are mostly indistinguishable to the untrained eye. For example, compare Queen Anne’s lace (Daucus carota) to poison hemlock (Conium maculatum). Your life may depend on it!
Cow parsnip (Heracleum maximum) is native to North America. A mature plant can be quite large, over 2 meters (6 feet) tall, which is at least twice the size of Queen Anne’s lace. Unlike its cousin the wild parsnip, the cow parsnip has white flowers.
Apparently, cow parsnip is a desirable garden plant in some locales. Surprisingly, it is listed as an endangered species in the state of Kentucky. That’s a curious designation for a plant that can cause phytophotodermatitis!
Recently (August 2018) cow parsnip has been spotted (by this author) along U.S. Forest Service roads leading to the Breadloaf Wilderness in the Green Mountain National Forest and along the Long Trail between Cooley Glen Shelter and Mount Grant. The mature plants were approximately 2 meters high and had already gone to seed but there were fresh yearlings nearby. A distinguishing feature of these plants (young and old) are the large, lobed leaves between 25–40 cm (10–15 in) wide. A closely-related species called the giant hogweed has similar characteristics but is typically much larger than the cow parsnip (see later section).
Queen Anne’s Lace
Queen Anne’s lace (Daucus carota), also known as wild carrot, is a very common species. The plants are small (1 meter or less) compared to other umbellifers. A mature plant will occasionally (<10%) have a dark red or purple flower in the center of the umbel but you have to look closely—at first glance, you might think you’re looking at a small bug nestled squarely in the center of the umbel. As the story goes, the red flower resulted from a blood droplet when Queen Anne pricked herself with a needle while embroidering the lace.
Its name suggests a dainty garden flower but be careful—Queen Anne’s lace is said to cause phytophotodermatitis (although the plant has smallish leaves with little sap). In any case, Queen Anne’s lace is reported as an invasive species in numerous states, including Washington, Minnesota, Michigan, and Ohio. Here in west central Vermont (summer 2018), it is everywhere. Indeed, there’s a stand of Queen Anne’s lace within 50 meters of my front door. Now I know why the local landscape artists wear long pants in the 90-degree heat when mowing and trimming the lawn.
Apparently, the seeds of Queen Anne’s lace have been used as both a contraceptive and an abortifacient for centuries. Search for “Daucus carota contraceptive abortifacient” for relevant references.
The real danger of Queen Anne’s lace (and the reason it is #2 on the list as opposed to #1) is its close resemblance to poison hemlock (Conium maculatum). Note well that the seeds of the poison hemlock plant (indeed, the entire plant) are highly poisonous! To be safe, do not gather seeds (or other plant parts) from the fields or woods unless you know what you’re doing.
Taxonomically speaking, wild parsnip is the same plant you buy in the grocery store. Like many of the plants in the carrot family, the parsnip (Pastinaca sativa) is a biennial. If you harvest the plant in its first year, you get a yummy root vegetable. By the second year, the root will have become woody and inedible, and if left unharvested, the plant will flower, go to seed, and spread vociferously.
The wild parsnip is classified as invasive in Vermont. Unlike Queen Anne’s lace, this author has not seen wild parsnip along the state’s roadways and trails (summer 2018), which includes a significant portion of the Long Trail, from Brandon Gap to Wind Gap, south of Camel’s Hump. However, there have been reported sightings of wild parsnip at Long Trail trailheads in southern Vermont. Open, disturbed areas such as pastures, fields, roadsides and trailhead parking areas are the perfect habitat for infestations of invasive plants.
From May to October, it is relatively easy to identify wild parsnip since it is the only species listed above with yellow flowers. The other umbellifers have white flowers. Still other members of the carrot family have pink or purple flowers.
Since the parsnip can cause phytophotodermatitis at any point in its life cycle, gardeners will know to wear protective clothing when working with this plant (and its cousins) in the garden. In the wild, unless you know what you’re doing, it is best to avoid the parsnip altogether. Just ask the woman from Vermont!
See “Wild parsnip: It’s everywhere and it’s delicious” for a different perspective on this infamous plant. Then read the section on spotted water hemlock below to understand why gathering parsnip roots in the wild is potentially life-threatening.
The giant hogweed (Heracleum mantegazzianum) was formally declared a noxious weed by the Federal Noxious Weed Act of 1974. The plant can grow to a staggering 5 meters (16 feet) in height with hollow stems up to 10 centimeters (4 inches) in diameter. In Maine, horticulturists have described the giant hogweed as “Queen Anne’s lace on steroids.”
Like its sibling the cow parsnip (Heracleum maximum), the giant hogweed can cause phytophotodermatitis. A plant this size is likely to have lots of sap, so beware.
By some accounts in the popular literature, the giant hogweed is thought to be a poisonous species but this is not true. While the giant hogweed is phototoxic (i.e., it can cause phytophotodermatitis), it is not poisonous. See the following two sections for examples of poisonous species in the Apiaceae family.
The giant hogweed is classified as invasive in Vermont.
Poison hemlock (Conium maculatum) is easily confused with other species in the carrot family (see the section on Queen Anne’s lace above). Many of the features of poison hemlock are shared by other umbellifers. This makes poison hemlock especially dangerous.
The toxic properties of poison hemlock have long been understood. Read Plato’s account of Socrates’ death allegedly caused by hemlock poisoning, which apparently was the preferred method of capital punishment in ancient Greece.
Spotted Water Hemlock
Spotted water hemlock (Cicuta maculata) is another biennial in the carrot family. Like the cow parsnip, the spotted water hemlock is native throughout North America.
In its first year, the spotted water hemlock has been mistaken for the parsnip since both have white tuberous roots. Don’t make that mistake! All parts of the water hemlock (especially the roots!) are highly poisonous. In fact, the spotted water hemlock is often characterized as the most poisonous plant in North America.
An Ounce of Prevention
The first and best line of defense against phytophotodermatitis is to avoid contact with phototoxic substances in the first place:
- Avoid contact with the Apiaceae family of plants and other biological agents known to have phototoxic effects. Do not incinerate phototoxic plants and agents since this will serve to disperse the phototoxic substances more widely.
- In situations where contact with phototoxic plants is likely, wear long pants and a long-sleeve shirt. In the garden or the field, wear gloves as well.
- If protective clothing is not available, apply sunscreen to exposed areas. This will provide some measure of protection if contact is made.
- After an outdoor activity, take a shower or a bath as soon as possible. Wash your clothing and then wash your hands after handling the dirty clothes.
- While hiking or backpacking, stay on the trail. This not only minimizes possible contact with phototoxic plants, but it’s also the best way to Leave No Trace.
A second line of defense is to avoid sunlight, so as not to activate a phototoxic substance:
- If you come in contact with a phototoxic substance, immediately wash the affected area and avoid any further exposure to sunlight.
- Stay indoors, if possible. Be careful to avoid light shining through windows.
- If staying indoors is not an option, cover the affected area with sun protective clothing.
- In lieu of sun protective clothing, apply sunscreen to affected areas after washing.
Phytophotodermatitis is triggered by long wavelength ultraviolet light (called UVA) in the range of 320–380 nanometers, so the best sun protective clothing and sunscreen products will block these wavelengths of UVA radiation.
In 2011, the U.S. Food and Drug Administration (FDA) established a “broad spectrum” test for determining a sunscreen product’s UVA protection. Sunscreen products that pass the test are allowed to be labeled as “Broad Spectrum” sunscreens, which protect against both UVA and UVB rays.
There is no equivalent test or FDA-approved labeling for sun protective clothing. Some clothing is labeled with an Ultraviolet Protection Factor (UPF) but test results from Consumer Reports suggest that UPF is an unreliable indicator of UV protection.
If in doubt, consult a dermatologist for specific product recommendations.
Spread the Word, Not the Plants!
Leonard, Jayne. “Phytophotodermatitis: When plants and light affect the skin.” Medical News Today. MediLexicon, Intl., 19 August 2017. Web resource retrieved 8 August 2018.
Davis, Dawn. “Sun-related Skin Condition Triggered by Chemicals in Certain Plants, Fruits.” Dermatology, Mayo Clinic, 12 August 2011. Web resource retrieved 8 August 2018.