Wicked Plants: The Weed That Killed Lincoln's Mother and Other Botanical Atrocities - Amy Stewart (2009)


Phototoxic plants harness the power of the sun to do their damage, using sap that burns the skin when exposed to light. In some cases, eating the plant or its fruits makes a person more susceptible to sunburn.



Heracleum mantegazzianum


This weedy, invasive member of the carrot family looks like the older brother of Queen Anne’s lace. It’s a beefy, sturdy plant that grows over ten feet tall and pushes other plants out of their habitats in streams and meadows. It is also one of the most phototoxic plants you might encounter. One botany textbook shows a round slice of stem placed on a man’s arm; within a day, a circular red welt appears, and after three days, it begins to blister. The wound looks disturbingly like the severe burn a car’s cigarette lighter would cause.


Apium graveolens


Another member of the carrot family, this plant is susceptible to a disease called pink rot fungus (Sclerotinia sclerotiorum). The main defense mechanism is to produce more phototoxic compounds to kill off the fungus. Farmworkers and handlers of celery routinely get burns on their skin that show up under sunlight, and people who eat large quantities of celery are at risk as well. One medical journal cited the case of a woman who ate celery root and then went to a tanning booth, ending up with a severe sunburn.


Peucedanum galbanum


This aptly named plant is also a member of the carrot family; its leaves resemble those of celery. The plants flourish in South Africa; tourists climbing Table Mountain near Cape Town are warned to avoid it. Simply brushing past it can cause a reaction, and hikers who accidentally break off a branch may suffer a severe rash from contact with the sap. The rash doesn’t appear for two or three days after contact with the plant and is made much worse by exposure to sunlight. The blisters can last a week or more and may leave brown spots on the skin for years.


Citrus aurantifolia, others


Limes and some other citrus fruits contain phototoxic compounds in the oil glands found in the outer rind of the fruit. One medical journal reported on a group of children at a day camp who broke out in unexpected rashes on their hands and arms. Doctors determined that the only children who were affected were those who had gone to a crafts class. They had been using limes to make pomander balls, and piercing the lime peel with scissors spread enough oil on their hands and arms to cause a reaction.

Orange marmalade and other foods containing citrus peel or citrus oil may cause a reaction. Oil of bergamot, a small, pear-shaped citrus, is a popular fragrance ingredient; any citrus-based perfume or lotion could also burn.


Melicope anisata syn. Pelea anisata


The mokihana blossom is the official flower of the Hawaiian island of Kauai. Tourists are often presented with a lei made of the dark green citruslike mokihana fruit, which are about the size of grapes. The oils are also highly phototoxic: a few years ago, a tourist wore a mokihana lei for about twenty minutes. Within a few hours, a painful, blistering rash appeared on her neck and chest in the precise shape of the lei. It eventually faded on its own, but the marks remained visible for two months.



A number of plants used in herbal teas, potpourris, lotions, or other concoctions can be phototoxic, although symptoms may not show up for a few days. Medical case studies report reactions from Saint-John’s-wort, rosemary, marigold, rue, chrysanthemum, fig leaf, and others.

A tourist wore a mokihana lei for about twenty minutes. Within a few hours, a painful, blistering rash appeared on her neck and chest in the precise shape of the lei.



Manchineel Tree


Tourists vacationing in the Caribbean or on the Central American coast are routinely warned about the hazards of the manchineel tree. As a member of the Euphorbiaceae family, it produces a highly irritating sap that can squirt out of the tree when a twig is snapped off. It also produces a toxic fruit that causes blistering in the mouth and makes the throat swell closed. Even lounging under the trees might be dangerous: rain dripping off them could cause rashes and itching.


Beaches on tropical islands, Florida everglades

Caribbean islands

Beach apple, manzanillo

The trees are irresistible to tourists. Despite her medical training, a radiologist visiting the island of Tobago was tempted to taste the green fruit that she found lying on the beach. When she took a bite, she found it to be sweet and juicy, like a plum. It took only a few minutes for a burning sensation to start in her mouth. Pretty soon, her throat closed so tightly that she could hardly swallow. The nearest medical remedy, a piña colada, helped a little, but probably only because of the milk it contained.

Captain James Cook encountered the trees on his voyage, and he and his crew also had a nasty encounter with the toxic tree. The men were in need of supplies; Cook ordered them to begin by collecting some fresh water and chopping manchineel wood. Some of the crew members made the mistake of rubbing their eyes, and they were reportedly blinded for two weeks as a result. There’s no record of whether they actually burned the wood, but if they had, the smoke would have been particularly noxious.

Even lounging under the trees might be dangerous: rain dripping off them could cause rashes and itching.

The manchineel tree’s powers have been exaggerated in art and legend. The tree made its way into the 1865 opera L’Africaine by German composer Giacomo Meyerbeer. A heartbroken island queen who is secretly in love with an explorer throws herself under the manchineel tree and draws her last breath, singing:

Your gentle perfume, they say, gives a fatal bliss
Which for a moment transports one to heaven
And then brings on the slumber without end.

Meet the Relatives Part of the Euphorbiaceae or spurge family, which includes a number of other trees and shrubs that produce milky, toxic sap.