Beautiful Invader
1 Imagine yourself taking a walk on a summer day—somewhere in a lazy meadow, near a stream. All along the stream banks and up through the grasses in the meadow, a flowering plant grows from three to ten feet tall. You admire the tiny flowers and their stunning rosy-purple color. You whip out your cell phone and are about to capture a photo when you hear a scolding voice in your head ask: "Why are you about to take a picture of purple loosestrife? It's not something to celebrate. It's an invasive species!"
2 Purple loosestrife isn't native to North America. It is originally from Europe and Asia. In North America, purple loosestrife grows so thickly and spreads so rapidly that it crowds out native grasses and other flowering plants. Furthermore, wildlife that depends on native plants for food and shelter suffer when purple loosestrife moves in. Because purple loosestrife can destroy the natural balance of an environment, some people believe that we should eliminate this flowering invader.
3 Purple loosestrife plants first arrived in the northeastern United States and Canada in the 1800s from Europe. Its seeds were often concealed in soil that ships crossing the Atlantic used as ballast, or weight added to keep a ship stable in the water. Once ashore in North America, the ships dumped the ballast, and the stowaway seeds took root and flourished in their new home. In addition, some immigrants brought purple loosestrife seeds with them. They thought it would be nice to have this familiar plant in their new country to use in flower arrangements and in herbal medicines. They never dreamed that the plant could harm the environment.
4 Today, purple loosestrife grows in almost every U.S. state. A great deal of money and effort has been invested trying to get rid of it. Many states classify the aggressive plant as a noxious, or harmful, weed. In some states, it is illegal to buy, sell, plant, or transport the species. But what makes purple loosestrife a plant "plague"? One problem is the way the plant grows. Each plant produces from 30 to 50 stems on strong stalks. In many regions, these stems bloom from June to September. Each stem is covered with tiny flowers. Each flower forms a seed pod bursting with seeds. A single stalk of purple loosestrife can yield from 100,000 to 300,000 seeds per year. A single plant can produce as many as 2 to 3 million seeds every year.
5 Another issue is how quickly purple loosestrife spreads. Its seeds are small and lightweight. A breeze or the gentle current of a stream is enough to carry purple loosestrife seeds to new territory where it can vanquish native vegetation. Meanwhile, underground, the plant sends out new root stems that grow as much as one foot per year. From every new root stem, new plant stalks emerge—each of which produces new flowers and thousands more seeds.
6 What can be done to stop purple loosestrife? Several remedies have been tried, but each has drawbacks. For example, people have tried simply uprooting purple loosestrife, but usually seeds and bits of root lurk in the soil and the purple loosestrife returns. Certain insects have been introduced that eat purple loose strife's roots and leaves. However, these natural enemies may feed on beneficial native plants as well. Plant-killing chemicals can effectively dispose of purple loosestrife, but they must be used very carefully so that they don't also destroy desirable vegetation.
7 There may not be a perfect solution, but land management agencies are looking for new ways to combat purple loosestrife. One such approach involves getting the public to help do battle against the plant. Some agencies train volunteers to patrol natural areas. They learn to identify purple loosestrife and report on places where it has begun its takeover. Volunteers are encouraged to submit photos of locations where purple loosestrife is growing. Perhaps your impulse to photograph purple loosestrife was a good idea after all! With an army of volunteers in place who can pinpoint areas where purple loosestrife is just starting to invade, environmental agencies hope to be able to respond to the flowering trespassers before they overwhelm native plant life.
8 Can purple loosestrife be removed from an entire continent? Perhaps not, but scientists are optimistic that it can be eradicated in some places and kept from spreading in other places where it cannot be completely eliminated. Laws that ban the selling and transporting of purple loosestrife; further study of its natural enemies; careful use of herbicides; and greater public awareness of how invasive species like purple loosestrife can damage ecosystems will go a long way toward improving the outlook for natural areas across North America.
Which sentence states a central/main idea in the passage?