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The Purple loosestrife (Lythrum salicaria) is a controversial plant, regarded both as a Friend and a Foe. In Europe, where the plant is native and commonly found in wetland landscapes, its beautiful purple flowers are admired both in nature and when introduced into gardens. However, in North America, where the plant was introduced by immigrants in the early 1800s, L. salicaria has become a pest, conquering vast areas and displacing native plants.
The exceptional success of the newcomer in the New World is primarily attributed to its escape from natural enemies. In the original habitats, the purple loosestrife is controlled and kept in check by plant-eating insects, especially beetles. In America, the alien plant can flourish, and the resources spared from defence are invested in extra growth and reproduction. As a result, the purple loosestrife now occupies all the US states except Florida.
Besides the escape of enemies, the purple loosestrife has merits of its own. Hybridization between plants from various origins results in new genomes, enhancing the vitality of the alien.
The purple loosestrife tolerates harsh environmental conditions, including dryness and flooding. On the warming planet, the species is one of the beneficiaries of climate change.
The newcomer is an undeniable competitive stress factor for native biota. However, the long-term ecological impacts of the purple loosestrife may be relatively minor. In several regions, it has become an established part of wetlands. The abundant riches the flowers provide are a priceless gift for pollinating insects, benefiting agriculture during dry seasons. The purple loosestrife plant is valuable in providing compounds used in medical preparations.
Although the purple loosestrife is not an agricultural weed, due to its damage to natural biota, the plant is included in the list of the 100 most deleterious alien organisms in the world. Besides the Americas, the plant has now been established - and is considered a worrisome alien - in Africa and Oceania.
