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

STOP AND SMELL THE RAGWEED

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.

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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:

RAGWEED

Ambrosia spp.

   

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.

YEW PINE

Podocarpus macrophyllus

   

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.

PEPPER TREE

Schinus molle or S. terebinthiefolius

   

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 TREE

Olea europaea

   

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.

MULBERRY

Morus spp.

   

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

HIMALAYAN CEDAR

Cedrus deodara

   

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.

BOTTLEBRUSH

Callistemon spp.

   

A popular, showy shrub in North America, Europe, and Australia. The long, bristlelike red stamens release golden pollen from the tips. The pollen is triangular in shape and lodges in the sinuses, making it a particularly vicious allergen.

JUNIPER

Juniperus spp.

   

This evergreen is a serious but overlooked source of allergens. The males produce cones, along with large quantities of pollen. Some junipers have both male and female organs on one plant (monoecious), which means that they might produce some berries but will also shed pollen.

BERMUDA GRASS

Cynodon dactylon

   

One of the most popular grasses for lawns in the South and warm-weather climates throughout the world, it is also the most allergenic. It blooms steadily, and the flowers often grow so low that lawn mowers miss them. New varieties don’t produce any pollen at all, but older varieties are so problematic that some cities in the Southwest have banned them.

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DESTRUCTIVE

Kudzu

PUERARIA LOBATA

Kudzu to the rescue!” So proclaimed a 1937 Washington Post article about the powers of this exotic vine to control erosion. And indeed, for almost a hundred years the vine enjoyed the enthusiastic support of American gardeners and farmers.

FAMILY:
Fabaceae

HABITAT:
Warm, humid climates

NATIVE TO:
China; introduced to Japan in the 1700s

COMMON NAMES:
Mile-a-minute vine, the vine that ate the South. To the Japanese, the word kudzu means “rubbish,” “waste,” or “useless scraps.”

The Centennial Exposition, held in 1876 in Philadelphia, was a carnival of wonders. Roughly ten million Americans were introduced to the telephone, the typewriter, and a miraculous new plant from Japan: kudzu. Plant enthusiasts loved the flowers’ fruity, grapelike fragrance and the fact that the vine could scramble over a trellis so quickly

Soon farmers realized that livestock would eat the vine, making it a useful forage crop. Kudzu gripped the soil and stopped erosion. A government program encouraging the use of the vine gave kudzu all the encouragement it needed.

Kudzu had other plans for the South. The vine made itself at home, growing up to a foot per day during the warm, humid summers. This plant is born to run: Over two dozen stems emerge from a single crown, and each of those vines can stretch to one hundred feet. A single massive tap root can weigh up to four hundred pounds. Each individual leaf can twist and turn so that it receives the maximum amount of sunlight, making the vine particularly efficient at harnessing the sun’s energy and keeping rays from reaching the plants below it.

Kudzu shrugs off cold weather and spreads by underground rhizomes and seeds, which can survive for several years before sprouting. It strangles trees, smothers meadows, undermines buildings, and pulls down power lines. Southerners say they sleep with the windows closed to keep it from sneaking into the bedroom at night.

The vine covers seven million acres in the United States. The damage it has caused is estimated in the hundreds of millions. At the Fort Pickett military base in Virginia, kudzu overwhelmed two hundred acres of training land. Even M1 Abrams battle tanks couldn’t penetrate the rampant growth.

But the South has not surrendered. Aggressive herbicide campaigns, controlled burns, and repeated slashing of new growth can keep kudzu in check. Southerners also fight back by eating the vine that is eating them: fried kudzu leaves, kudzu blossom jelly, and kudzu stem salsa all put a bad plant to good use.

Meet the Relatives Kudzu is a legume; it is related to such useful plants as soybeans, alfalfa, and clover.