Wicked Plants (10 page)

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
.

CAULERPA TAXIFOLIA

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.

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.

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.

A poisonous seed will only kill you if you chew it and swallow. A painful rash can only spread if you brush up against the leaves. But some plants have figured out how to extend their reach by releasing highly irritating allergens into the air.

There’s a reason why seasonal allergies seem to get worse every year. Gardeners and landscapers, in an attempt to be tidy, prefer to plant male trees and shrubs. The females drop fruit, leaving a mess all over the sidewalk or the lawn. But a male tree produces only small, well-behaved flowers—that is, if your definition of
well behaved
includes spewing plant sperm into the air for weeks on end.

In the 1950s and 1960s diseased American elm trees
were replaced with male varieties of wind-pollinated trees. As a result, some cities, particularly in the Southeast, are virtually uninhabitable for people with serious allergies and asthma.

Homeowners are surprisingly reluctant to remove these trees. One allergen expert remembers a family with a huge male mulberry tree in their garden. After blasting the tree with a hose in a misguided attempt to wash off the pollen, both the husband and wife felt their throats close and had to lock themselves in the bathroom all night just to be able to breathe. The pollen had germinated in water, releasing even more allergens than before.

Consider banishing these plants from the yard:

A versatile weed that flourishes throughout the United States and across Europe. A single plant can produce a billion grains of pollen during a season. The pollen remains airborne for days and can travel several miles, affecting some 75 percent of allergy sufferers and creating cross-allergies with foods that have similar proteins, including cantaloupe, banana, and watermelon. Ragweed releases more pollen when carbon dioxide levels are higher, so global warming will only make the situation worse.

A shrub or small tree popular as a street tree or as a foundation plant in landscapes, this plant is a heavy pollen producer, and the fact that it is often planted right under windows in suburban landscapes means that allergy sufferers may wake up with a sore throat that will only get sicker if they spend the day in bed.

A controversial landscaping tree that can be invasive and cause a nasty skin rash. The berries are poisonous if eaten. The male trees send copious amounts of pollen into the air over a long blooming season. Because it is related to poison ivy and other members of the toxicodendron genus, people who are especially sensitive to those plants will also suffer around pepper trees. It produces an oil that can vaporize into thin air, causing people to develop asthma, eye inflammation, and other reactions just from being nearby.

Olive pollen is so highly irritating, owing to the number of different allergens it contains, that some cities are trying to banish the tree entirely. The city of Tucson, Arizona, has passed an ordinance banning the sale or planting of olive trees.

One of the most potent sources of spring allergies, this plant sheds billions of pollen grains that linger on patios and get tracked indoors.

A fast-growing cedar reaching up to eighty feet tall and forty feet wide, found in gardens and parks throughout mild winter areas in North America and Europe. The small, male cones shed pollen in the fall. Many seasonal allergy sufferers are sensitive to cedar, making this an unbearable tree to be around.