Wicked Plants (17 page)

Darwin wasn’t the only one who was mad about loosestrife. European settlers brought the meadow plant to America, where it quickly established itself. Gardeners and naturalists had a real affection for the tall, vigorous wildflower and its gorgeous spikes of purple blooms. For most of the twentieth century, horticulturalists enthusiastically recommended it for difficult spots in the garden, such as shady areas or beds with poor soil or bad drainage. As late as 1982 garden writers recognized its weedy tendencies but still referred to it as a “handsome rascal,” as if to suggest that boys will be boys, and gardeners should love the plant for its aggressive nature.

How wrong they were. Purple loosestrife is surely one of the worst invaders the American landscape has seen. It has marched across forty-seven states and most of Canada, and has also made its way into New Zealand, Australia, and across Asia. The plant easily reaches ten feet tall and five feet wide, and as many as fifty stems can sprout from a single, sturdy perennial tap root. If the rootstock wasn’t vigorous enough, a single specimen can produce over 2.5 million seeds in a season. Those seeds can live for twenty years before they sprout.

Purple loosestrife clogs wetlands and waterways, choking out other plant life and eliminating food sources and habitat for wildlife. An estimated sixteen million acres have been infested with purple loosestrife in the United States alone, and eradication campaigns cost about $45 million per year. The plant is classified as a federal noxious weed and is also illegal to transport or sell in many states. Although other species are sold as noninvasive or sterile alternatives to the dreaded purple loosestrife, native plant experts recommend steering clear of anything labeled
Lythrum.

Loosestrife is native to Europe but does not cause the same damage there. That fact provided a clue to controlling it in the United States. Chemical sprays, mechanical cultivations, and other
controls weren’t particularly successful, but then researchers tried importing the same bugs that feed on the plant in Europe. Now a few species of root weevils and leaf-eating beetles have been released as a form of biological control, and it’s working. So far, it does not appear that the bugs eat native plants, but introducing one exotic creature to control another always has its risks.

Meet the Relatives
     Crape myrtles and cuphea, a genus of shrubs with fuchsialike flowers.

Some plants just have a way of taking over. They are not above choking the competition, robbing it of food, or even releasing poisonous compounds underground to get it out of the way. These plants are not just invasive; they’re homicidal.

A freshwater aquatic plant that migrated from Asia to Florida in the 1960s. It quickly established itself in lakes and rivers, where it puts down sturdy roots and grows up to an inch a day until it reaches the surface. Some individual plants are twenty-five feet long. Because hydrilla is attracted to sunlight, once the plant reaches the water’s surface it will often form a thick mat of vegetation that chokes out aquatic life and makes navigation difficult. Water grows stagnant around a hydrilla infestation, encouraging mosquitoes to breed. It is found in warm, freshwater environments around the United States, and it is almost impossible to eliminate because even the smallest fragment can regenerate. One scientist compared it to herpes. “Once you’ve got it,” he said, “you’ve got it forever.”

The U.S. Department of Agriculture has placed most species of dodder on its federal noxious weeds list. This plant parasite looks like an alien life form that has come to suck the life out of the earth’s vegetation, and that’s not too far from the truth. The long, seemingly leafless stems grow in otherworldly colors like orange, pink, red, and yellow. (In fact, dodders do have something like leaves, but they are really just tiny, almost invisible scales.) Dodder does a poor job at photosynthesis, which is why it needs to get its nutrition from another plant. In fact, after the seeds germinate, the young shoots only have about a week to find a host plant or they will die. The seedlings grow in the direction of possible host plants. Laboratory tests have proven that dodders will reach in the direction of the scent of the plant, even if there are no plants
growing nearby at all, showing that it actually does have an animal-like sense of smell.

Once a dodder finds a host plant, it wraps itself around its victim, injects tiny fungal structures into it, and sucks out the plant’s nutrients. A single dodder can invade several plants, feeding on all of them at once and eventually killing them. A field smothered in dodder looks like it has been attacked by Silly String.

The worst terrestrial weed, according to many experts. Found throughout the world in temperate climates, it spreads quickly, crowding out native plants and invading croplands. Tilling only encourages it by breaking up underground tubers, each of which produces more plants. But what makes purple nutsedge particularly vicious is its ability to release allelopathic compounds into the soil, which actually kill the competition. Gardeners who allow purple nutsedge to go unchecked will find that it not only has taken over but also poisons other plants.

This free-floating aquatic fern can double its population every two days, forming dense mats up to three feet deep on the water’s surface. One of the largest infestations was a stunning ninety-six square miles. Giant salvinia is found in freshwater lakes, wetlands, and streams throughout the southern United States. It thrives in nutrient-rich water, so it grows particularly vigorously in water enriched by fertilizer runoff or sewer-treatment plant waste.

Known for the decidedly unfriendly habit of wrapping around another tree and strangling it to death. The seeds, which are spread with the help of birds, will often germinate high in the canopy of another tree. Strong, woody roots start wrapping around the host tree and reaching for the ground. Sometimes the roots will completely encircle the tree trunk, and when the tree dies the hollowed-out interior remains, leaving the fig tree in the shape of a giant drinking straw.

Although strangler figs are decidedly creepy, they are generally not considered invasive but are looked upon as an interesting botanical curiosity that has its own niche in the ecosystem.

DICHAPETALUM CYMOSUM OR D. TOXICARIUM

Several plants produce the deadly poison sodium fluoroacetate, but the best-known sources are a couple of flowering trees in West Africa,
Dichapetalum cymosum
and
D. toxicarium.
Because of the plant’s geographic isolation, the trees didn’t pose much of a threat until the 1940s, when scientists discovered that they could extract the poison and create a potent chemical for controlling rats and predatory animals like coyotes.

The poison is odorless and tasteless, and only a minute amount is required to kill a mammal. Death comes within a few hours, usually preceded by vomiting, seizures, heart irregularities, and respiratory distress. Survivors may experience permanent damage to vital organs. The poison lingers in the body; if the animal is eaten by another animal, it can poison the rest of the food chain. For this reason, ratbane is sometimes referred to as “the poison that keeps on killing.”

Sodium fluoroacetate, which is also called Compound 1080, was used on and off until 1972, when the U.S. Environmental
Protection Agency (EPA) banned it along with sodium cyanide and strychnine. However, the agency later allowed the U.S. Department of Agriculture to continue using the poison in livestock protection collars. The collars contain fifteen milliliters of Compound 1080, and they can be fitted around the throat of sheep and cattle. When a coyote reaches for the jugular, it will get a toxic dose of this poison instead.

Use of the chemical for predator management is controversial. Some conservationists argue that strapping such a potent toxin to the necks of livestock could inadvertently result in the poisoning of fish, birds, and water supplies. Aerial spraying in New Zealand to kill invasive rats and possums has prompted outcry from activists who oppose the use of this indiscriminate killer.

The poison attracted attention in 2004, when it was used by a mysterious serial killer to wipe out scores of animals in a São Paulo zoo. No trace of the poison was found in the animals’ food or water, which suggested a very sophisticated killer with good access to the animals. Camels, porcupines, chimpanzees, and elephants died while zoo staff scrambled to put in security measures.
Although the poison is banned in Brazil, the killer managed to smuggle it in and cause terrible destruction.

In 2006 a little-noticed notation in the Iraq Study Group’s report revealed that one of the chemical stockpiles found by coalition forces contained vials of Compound 1080 manufactured by a company in Oxford, Alabama. How did Saddam Hussein get it and what did he plan to do with it? Representative Peter DeFazio, a Democrat from Oregon, wasn’t sure, but he thought that the risk of the substance’s getting used as a chemical weapon outweighed its benefits as a form of livestock control. According to news reports, the EPA told him that it would only ban the chemical upon the recommendation of the U.S. Department of Homeland Security, and that department told him that it could not recommend the banning of any particular chemical. He introduced a bill outlawing sodium fluoroacetate, but it died in committee.

Meet the Relatives
     Ratbane is related to a few other flowering trees and shrubs found in Africa and South America, including those in the genuses
Tapura
and
Stephanopodium.