BOTANICAL CRIME FAMILIES - Wicked Plants: The Weed That Killed Lincoln's Mother and Other Botanical Atrocities - Amy Stewart

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


Ever noticed how criminal tendencies tend to run in the family? A few plant families seem to have more than their fair share of black sheep. The characteristics that set them apart—stinging hairs or milky sap or lacy foliage—also give them away.




Nightshades represent some of the best and worst plants humans have ever encountered. Potatoes, peppers, eggplants, and tomatoes are among the more respectable members of this family. However, when European settlers first encountered tomatoes in the New World, they believed them to be poisonous like the other nightshades they knew. Tomatoes, after all, bear a familial resemblance to their cousin, deadly nightshade, and other dangerous nefarious relatives like the narcotic mandrake, the evil weed tobacco, and the poisonous and intoxicating henbane, belladonna, and datura.

Nightshades have long been viewed with suspicion and distrust. John Smith, a seventeenth-century philosopher, compared the “congealing vapour that ariseth from sin and vice” to the evil powers of “that venemous deadly nightshade, which drives its cold poison into the understandings of men.” In fact, many nightshades contain tropane alkaloids that cause hallucinations, seizures, and deadly comas.

The petunia is also a nightshade; in fact, knowing what a petunia flower looks like might just provide a clue for recognizing some other members of this family. Otherwise, an unfamiliar plant that produces small, round fruit and has the general growth habit of a tomato or eggplant should be viewed with some caution.



The trees and shrubs in this family typically produce a drupe, a kind of fruit in which the seed is surrounded by a hard pit, which is in turn surrounded by sweet, juicy flesh. (Mangoes are one example, as are the unrelated stone fruits like peaches and cherries.) But what the cashew family does best is produce a toxic resin that brings on painful and long-lasting rashes. And don’t light a member of the cashew family on fire—it will produce a noxious smoke that burns the lungs.

Poison ivy, poison oak, and poison sumac are perhaps the most feared members of this family. Mango and cashew trees also produce the irritating resin known as urishol, as does the lacquer tree. In fact, people who are highly sensitive to poison ivy or one of its cousins may experience a cross-sensitivity to mango rind or a lacquer-covered box. Other relatives include the pistachio tree, the ginkgo tree, the poison-wood tree, and the pepper tree.



These small and often harmless-looking plants are best known for that unique anatomical feature, urticating hairs. The fine hairs may look as innocent as peach fuzz, but they often contain a minute dose of poison that is released when the hairs get under the skin. The medical term for painful, itchy hives, urticaria, gets its name from the skin inflammation brought on by stinging nettles.

Most nettles are low-growing plants that superficially resemble herbs like mint or basil, with toothed edges. The Australian stinging tree, widely considered the world’s most painful plant, is a member of the nettle family, but the best-known member of this family is the stinging nettle, Urtica dioica. The hairs are so fine that people unfamiliar with the plant might not even notice them. In addition to the stinging hairs, nettles can also be identified by the small clusters of flowers that emerge from the joint where the leaf connects to the stem. However, the best advice for avoiding the nettle family is to resist the temptation to stroke an unfamiliar fuzzy or hairy leaf.



The highly irritating, milky sap produced by most members of the spurge family sets it apart. Gardeners may recognize the more common euphorbias that are popular in Mediterranean gardens, but other members of this family are not as obviously related: poinsettia, pencil cactus, Texas bull nettle, castor bean, rubber tree, sandbox tree, mala mujer, milky mangrove, and manchineel are all spurges. Many of these can burn and scar the skin, but some, like castor bean, also contain powerful poisons that can kill if ingested. At the very least, plants that produce a milky sap should be handled with care, as they may burn skin and eyes. Some spurges can be identified by their colorful bracts; for example, consider the flowers of euphorbias or poinsettias.



This family conceals some notorious criminals among its otherwise healthy and beautiful members. Carrots, dill, fennel, parsley, anise, lovage, chervil, parsnips, caraway, coriander, angelica, and celery are all plants that a good chef couldn’t live without, but even they require some caution: many, including celery, dill, parsley, and parsnips are phototoxic, meaning that skin contact, combined with sun exposure, can cause a rash. One garden flower, bishop’s weed (Ammi majus), is so phototoxic that exposure to the seeds can permanently darken skin.

But the real danger is posed by relatives like water hemlock, poison hemlock, giant hogweed, and cow parsnip. These wild plants contain neurotoxins and skin irritants, but they so closely resemble their edible cousins that tragic mistakes have been made by hikers and cooks.

Identifying plants in the carrot family is fairly easy. Queen Anne’s lace is a typical example; like most members of the family, it produces fine, lacy foliage and flat-topped clusters of flowers called umbels, as well as a carrot-shaped root.





Khat played a small but pivotal role in the 1993 battle of Mogadishu in which two American Black Hawk helicopters were shot down. Gun-toting Somalian men stuffed khat leaves into their cheeks and raced around Mogadishu with a jittery high that lasted until late into the night, contributing to the violence and the deaths of American soldiers trapped at the crash site.


Tropical elevations above three thousand feet


Qat, kat, chat, Abyssinian tea, miraa, jaad

Author Mark Bowden found an interesting route into Somalia when he was researching his book Black Hawk Down: he flew on a khat plane. Because the leaves must be consumed fresh, Bowden had to pay for the amount of khat he was displacing that day. “What they did was offload two hundred pounds of khat so I could sit on the plane,” he said in an interview. “I paid for myself as if I were khat to get into the country.”

The leaves deliver a clear-headed euphoria that lasts for hours. In Yemen and Somalia up to three-quarters of adult men use the drug, stuffing a few leaves between their cheek and gum, in much the same way that coca is used in Latin America. And like coca, the khat plant has fueled wars between those who claim it is a benign cultural ritual that has been practiced for centuries and those who see it as a public health menace.

When a khat plane lands in Somalia, its cargo is unloaded and distributed in a matter of hours. Men lounge about in a blissed-out state, chewing their khat, tending to neither their families nor their jobs. Long-term use leads to aggression, delusions, paranoia, and psychosis. But the typical khat user is not deterred by these alarming symptoms. As one man put it, “When I chew it, I feel like my problems disappear. Khat is my brother. It takes care of all things.” Another man said, “You open up like a flower when you chew.”

Gun-toting Somalian men stuffed khat leaves into their cheeks and raced around Mogadishu with a jittery high that lasted until late into the night.

Catha edulis is a flowering shrub that flourishes in Ethiopia and Kenya, where it enjoys full sun and warm temperatures. The dark, glossy leaves emerge from red stalks, and young leaves may also be fringed in red. The plant reaches twenty feet or more in the wild, but only five or six feet in cultivation.

Its most potent ingredient, cathinone, is classifed in the United States as a Schedule I narcotic, putting it on the same footing as marijuana and peyote. The level of cathinone in the leaves drops sharply just forty-eight hours after harvest, a fact that turns drug smuggling into a wild race. Once the cathinone breaks down, all that is left is cathine, a very mild chemical similar to the diet pill ephedrine. For this reason, police have to move fast to get the plant to a drug lab. After forty-eight hours a major drug bust will become a diet pill raid.

Khat dealers in Seattle, Vancouver, and New York have been busted for selling bundles of leaves under the counter in small grocery stores that cater to Somalian immigrants. In 2006 Somalia’s Islamic movement outlawed the plant in the areas it controlled and stopped all flights arriving from Kenya in an attempt to crush the use of the plant. It remains to be seen whether Somalians will give up their drug, which has been called the opium of the people.

Meet the Relatives Khat is related to about thirteen hundred species of tropical and temperate vines and shrubs, including the highly poisonous staff vine, and the equally poisonous spindle shrubs known as Euonymus.




Killer Algae


In 1980 staff working at a zoo in Stuttgart, Germany, noticed an impressive strain of the tropical seaweed Caulerpa taxifolia in one of their aquariums. Usually it couldn’t handle the colder temperatures that Mediterranean fish require, but this particular specimen was lush, green, and hardy in the cold aquarium. What made it so different? Scientists believe that constant exposure to chemicals and ultraviolet light in the aquarium triggered a genetic mutation that made it particularly tough.


Killer algae thrives in the Mediterranean, along California’s Pacific coast, in the oceans off tropical and subtropical Australia, and in saltwater aquariums worldwide.

Originally discovered along the French coast, this algae is native to the Caribbean, east Africa, northern India, and elsewhere.

Caulerpa, Mediterranean clone

Word got around, and soon the staff at several aquariums wanted to try the plant in their exhibits. Someone brought it to Jacques Cousteau’s Oceanographic Museum in Monaco, where it escaped into the wild with just a little extra help. According to one report, in 1984 an employee cleaning the tanks tossed the leftover waste into the sea.

French biology professor Alexandre Meinesz first saw a patch of the algae growing in the Mediterranean Sea near the museum in 1989. He was surprised to see a tropical seaweed growing so vigorously in the cold water, and he warned his colleagues that the plant could become invasive.

The entire plant—its feathery fronds, sturdy stems, and tough rhizoids that anchor it to the ocean floor—is all just one giant cell that can span over two feet in length and grow about half an inch per day.

This set off a decade-long debate over the origin of the plant, the likelihood that it might become invasive, and the responsibility for combating an invasion if it happened. As committees were being formed and papers were being written, the algae made its way to sixty-eight sites around the world, covering twelve thousand acres of the ocean floor. Today, a lush, green carpet of C. taxifolia spans over thirty two thousand acres of oceans around the world, or about fifty square miles.

This is truly remarkable considering the fact that killer algae is a single-celled organism. The entire plant, including its feathery fronds, sturdy stems, and tough rhizoids that anchor it to the ocean floor, are all just one giant cell that can span over two feet in length and grow about half an inch per day. This makes it one of the world’s largest—and most dangerous—single-celled organisms.

Killer algae don’t kill human beings. The plant gets its nickname from a toxin called caulerpenin that poisons fish. This keeps marine life from nibbling on the plant, which is part of the reason it has spread unchecked in oceans around the world. The lush, green vegetation forms meadows ten feet deep on the ocean floor, choking out all other aquatic life. Fish populations are dying out, and waterways have become clogged with the plant.

This mutant aquarium strain of C. taxifolia is exclusively male, suggesting that the entire invasive population around the world stems from just one parent plant. It reproduces only through propagation: a chunk breaks off, gets chopped up in the undercarriage of boats, and then spreads throughout the ocean. The caulerpenin toxin forms a gel that heals the wound within an hour, allowing that fragment to grow and establish a meadow of its own.

Killer algae is classified as a noxious weed in the United States, which means that it cannot be imported into the country or shipped across state lines. It’s considered one of the world’s hundred worst invaders by the Invasive Species Specialist Group. Attempts to eradicate it haven’t met with much success, because chopping up the plant only helps it reproduce. One of the few success stories comes from San Diego, where an eleven-thousand-square-foot patch was destroyed by placing a tarp over it and pumping chlorine into it. Authorities haven’t claimed victory just yet: even a one-millimeter chunk of killer algae floating in the ocean could take root and spread again.

Meet the Relatives The edible sea lettuce (Ulva lactuca) and other small, green seaweeds are related to the menacing killer algae.